// SPDX-License-Identifier: GPL-2.0-only
/*
 *  mm/userfaultfd.c
 *
 *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
 *  Copyright (C) 2008-2009 Red Hat, Inc.
 *  Copyright (C) 2015  Red Hat, Inc.
 *
 *  Some part derived from fs/eventfd.c (anon inode setup) and
 *  mm/ksm.c (mm hashing).
 */

#include <linux/mm.h>
#include <linux/sched/signal.h>
#include <linux/pagemap.h>
#include <linux/rmap.h>
#include <linux/swap.h>
#include <linux/leafops.h>
#include <linux/userfaultfd_k.h>
#include <linux/mmu_notifier.h>
#include <linux/hugetlb.h>
#include <linux/list.h>
#include <linux/sched/mm.h>
#include <linux/mm_inline.h>
#include <linux/poll.h>
#include <linux/slab.h>
#include <linux/seq_file.h>
#include <linux/bug.h>
#include <linux/anon_inodes.h>
#include <linux/syscalls.h>
#include <linux/miscdevice.h>
#include <linux/uio.h>
#include <linux/file.h>
#include <linux/cleanup.h>
#include <asm/tlbflush.h>
#include <asm/tlb.h>
#include "internal.h"
#include "swap.h"

struct mfill_state {
        struct userfaultfd_ctx *ctx;
        unsigned long src_start;
        unsigned long dst_start;
        unsigned long len;
        uffd_flags_t flags;

        struct vm_area_struct *vma;
        unsigned long src_addr;
        unsigned long dst_addr;
        pmd_t *pmd;
};

static bool anon_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags)
{
        /* anonymous memory does not support MINOR mode */
        if (vm_flags & VM_UFFD_MINOR)
                return false;
        return true;
}

static struct folio *anon_alloc_folio(struct vm_area_struct *vma,
                                      unsigned long addr)
{
        struct folio *folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma,
                                              addr);

        if (!folio)
                return NULL;

        if (mem_cgroup_charge(folio, vma->vm_mm, GFP_KERNEL)) {
                folio_put(folio);
                return NULL;
        }

        return folio;
}

static const struct vm_uffd_ops anon_uffd_ops = {
        .can_userfault  = anon_can_userfault,
        .alloc_folio    = anon_alloc_folio,
};

static const struct vm_uffd_ops *vma_uffd_ops(struct vm_area_struct *vma)
{
        if (vma_is_anonymous(vma))
                return &anon_uffd_ops;
        return vma->vm_ops->uffd_ops;
}

static __always_inline
bool validate_dst_vma(struct vm_area_struct *dst_vma, unsigned long dst_end)
{
        /* Make sure that the dst range is fully within dst_vma. */
        if (dst_end > dst_vma->vm_end)
                return false;

        /*
         * Check the vma is registered in uffd, this is required to
         * enforce the VM_MAYWRITE check done at uffd registration
         * time.
         */
        if (!dst_vma->vm_userfaultfd_ctx.ctx)
                return false;

        return true;
}

static __always_inline
struct vm_area_struct *find_vma_and_prepare_anon(struct mm_struct *mm,
                                                 unsigned long addr)
{
        struct vm_area_struct *vma;

        mmap_assert_locked(mm);
        vma = vma_lookup(mm, addr);
        if (!vma)
                vma = ERR_PTR(-ENOENT);
        else if (!(vma->vm_flags & VM_SHARED) &&
                 unlikely(anon_vma_prepare(vma)))
                vma = ERR_PTR(-ENOMEM);

        return vma;
}

#ifdef CONFIG_PER_VMA_LOCK
/*
 * uffd_lock_vma() - Lookup and lock vma corresponding to @address.
 * @mm: mm to search vma in.
 * @address: address that the vma should contain.
 *
 * Should be called without holding mmap_lock.
 *
 * Return: A locked vma containing @address, -ENOENT if no vma is found, or
 * -ENOMEM if anon_vma couldn't be allocated.
 */
static struct vm_area_struct *uffd_lock_vma(struct mm_struct *mm,
                                       unsigned long address)
{
        struct vm_area_struct *vma;

        vma = lock_vma_under_rcu(mm, address);
        if (vma) {
                /*
                 * We know we're going to need to use anon_vma, so check
                 * that early.
                 */
                if (!(vma->vm_flags & VM_SHARED) && unlikely(!vma->anon_vma))
                        vma_end_read(vma);
                else
                        return vma;
        }

        mmap_read_lock(mm);
        vma = find_vma_and_prepare_anon(mm, address);
        if (!IS_ERR(vma)) {
                bool locked = vma_start_read_locked(vma);

                if (!locked)
                        vma = ERR_PTR(-EAGAIN);
        }

        mmap_read_unlock(mm);
        return vma;
}

static struct vm_area_struct *uffd_mfill_lock(struct mm_struct *dst_mm,
                                              unsigned long dst_start,
                                              unsigned long len)
{
        struct vm_area_struct *dst_vma;

        dst_vma = uffd_lock_vma(dst_mm, dst_start);
        if (IS_ERR(dst_vma) || validate_dst_vma(dst_vma, dst_start + len))
                return dst_vma;

        vma_end_read(dst_vma);
        return ERR_PTR(-ENOENT);
}

static void uffd_mfill_unlock(struct vm_area_struct *vma)
{
        vma_end_read(vma);
}

#else

static struct vm_area_struct *uffd_mfill_lock(struct mm_struct *dst_mm,
                                              unsigned long dst_start,
                                              unsigned long len)
{
        struct vm_area_struct *dst_vma;

        mmap_read_lock(dst_mm);
        dst_vma = find_vma_and_prepare_anon(dst_mm, dst_start);
        if (IS_ERR(dst_vma))
                goto out_unlock;

        if (validate_dst_vma(dst_vma, dst_start + len))
                return dst_vma;

        dst_vma = ERR_PTR(-ENOENT);
out_unlock:
        mmap_read_unlock(dst_mm);
        return dst_vma;
}

static void uffd_mfill_unlock(struct vm_area_struct *vma)
{
        mmap_read_unlock(vma->vm_mm);
}
#endif

static void mfill_put_vma(struct mfill_state *state)
{
        if (!state->vma)
                return;

        up_read(&state->ctx->map_changing_lock);
        uffd_mfill_unlock(state->vma);
        state->vma = NULL;
}

static int mfill_get_vma(struct mfill_state *state)
{
        struct userfaultfd_ctx *ctx = state->ctx;
        uffd_flags_t flags = state->flags;
        struct vm_area_struct *dst_vma;
        const struct vm_uffd_ops *ops;
        int err;

        /*
         * Make sure the vma is not shared, that the dst range is
         * both valid and fully within a single existing vma.
         */
        dst_vma = uffd_mfill_lock(ctx->mm, state->dst_start, state->len);
        if (IS_ERR(dst_vma))
                return PTR_ERR(dst_vma);

        /*
         * If memory mappings are changing because of non-cooperative
         * operation (e.g. mremap) running in parallel, bail out and
         * request the user to retry later
         */
        down_read(&ctx->map_changing_lock);
        state->vma = dst_vma;
        err = -EAGAIN;
        if (atomic_read(&ctx->mmap_changing))
                goto out_unlock;

        err = -EINVAL;

        /*
         * shmem_zero_setup is invoked in mmap for MAP_ANONYMOUS|MAP_SHARED but
         * it will overwrite vm_ops, so vma_is_anonymous must return false.
         */
        if (WARN_ON_ONCE(vma_is_anonymous(dst_vma) &&
            dst_vma->vm_flags & VM_SHARED))
                goto out_unlock;

        /*
         * validate 'mode' now that we know the dst_vma: don't allow
         * a wrprotect copy if the userfaultfd didn't register as WP.
         */
        if ((flags & MFILL_ATOMIC_WP) && !(dst_vma->vm_flags & VM_UFFD_WP))
                goto out_unlock;

        if (is_vm_hugetlb_page(dst_vma))
                return 0;

        ops = vma_uffd_ops(dst_vma);
        if (!ops)
                goto out_unlock;

        if (uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE) &&
            !ops->get_folio_noalloc)
                goto out_unlock;

        return 0;

out_unlock:
        mfill_put_vma(state);
        return err;
}

static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address)
{
        pgd_t *pgd;
        p4d_t *p4d;
        pud_t *pud;

        pgd = pgd_offset(mm, address);
        p4d = p4d_alloc(mm, pgd, address);
        if (!p4d)
                return NULL;
        pud = pud_alloc(mm, p4d, address);
        if (!pud)
                return NULL;
        /*
         * Note that we didn't run this because the pmd was
         * missing, the *pmd may be already established and in
         * turn it may also be a trans_huge_pmd.
         */
        return pmd_alloc(mm, pud, address);
}

static int mfill_establish_pmd(struct mfill_state *state)
{
        struct mm_struct *dst_mm = state->ctx->mm;
        pmd_t *dst_pmd, dst_pmdval;

        dst_pmd = mm_alloc_pmd(dst_mm, state->dst_addr);
        if (unlikely(!dst_pmd))
                return -ENOMEM;

        dst_pmdval = pmdp_get_lockless(dst_pmd);
        if (unlikely(pmd_none(dst_pmdval)) &&
            unlikely(__pte_alloc(dst_mm, dst_pmd)))
                return -ENOMEM;

        dst_pmdval = pmdp_get_lockless(dst_pmd);
        /*
         * If the dst_pmd is THP don't override it and just be strict.
         * (This includes the case where the PMD used to be THP and
         * changed back to none after __pte_alloc().)
         */
        if (unlikely(!pmd_present(dst_pmdval) || pmd_leaf(dst_pmdval)))
                return -EEXIST;
        if (unlikely(pmd_bad(dst_pmdval)))
                return -EFAULT;

        state->pmd = dst_pmd;
        return 0;
}

/* Check if dst_addr is outside of file's size. Must be called with ptl held. */
static bool mfill_file_over_size(struct vm_area_struct *dst_vma,
                                 unsigned long dst_addr)
{
        struct inode *inode;
        pgoff_t offset, max_off;

        if (!dst_vma->vm_file)
                return false;

        inode = dst_vma->vm_file->f_inode;
        offset = linear_page_index(dst_vma, dst_addr);
        max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
        return offset >= max_off;
}

/*
 * Install PTEs, to map dst_addr (within dst_vma) to page.
 *
 * This function handles both MCOPY_ATOMIC_NORMAL and _CONTINUE for both shmem
 * and anon, and for both shared and private VMAs.
 */
static int mfill_atomic_install_pte(pmd_t *dst_pmd,
                                    struct vm_area_struct *dst_vma,
                                    unsigned long dst_addr, struct page *page,
                                    uffd_flags_t flags)
{
        int ret;
        struct mm_struct *dst_mm = dst_vma->vm_mm;
        pte_t _dst_pte, *dst_pte;
        bool writable = dst_vma->vm_flags & VM_WRITE;
        bool vm_shared = dst_vma->vm_flags & VM_SHARED;
        spinlock_t *ptl;
        struct folio *folio = page_folio(page);
        bool page_in_cache = folio_mapping(folio);
        pte_t dst_ptep;

        _dst_pte = mk_pte(page, dst_vma->vm_page_prot);
        _dst_pte = pte_mkdirty(_dst_pte);
        if (page_in_cache && !vm_shared)
                writable = false;
        if (writable)
                _dst_pte = pte_mkwrite(_dst_pte, dst_vma);
        if (flags & MFILL_ATOMIC_WP)
                _dst_pte = pte_mkuffd_wp(_dst_pte);

        ret = -EAGAIN;
        dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
        if (!dst_pte)
                goto out;

        if (mfill_file_over_size(dst_vma, dst_addr)) {
                ret = -EFAULT;
                goto out_unlock;
        }

        ret = -EEXIST;

        dst_ptep = ptep_get(dst_pte);

        /*
         * We are allowed to overwrite a UFFD pte marker: consider when both
         * MISSING|WP registered, we firstly wr-protect a none pte which has no
         * page cache page backing it, then access the page.
         */
        if (!pte_none(dst_ptep) && !pte_is_uffd_marker(dst_ptep))
                goto out_unlock;

        if (page_in_cache) {
                folio_add_file_rmap_pte(folio, page, dst_vma);
        } else {
                folio_add_new_anon_rmap(folio, dst_vma, dst_addr, RMAP_EXCLUSIVE);
                folio_add_lru_vma(folio, dst_vma);
        }

        /*
         * Must happen after rmap, as mm_counter() checks mapping (via
         * PageAnon()), which is set by __page_set_anon_rmap().
         */
        inc_mm_counter(dst_mm, mm_counter(folio));

        set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);

        if (page_in_cache)
                folio_unlock(folio);

        /* No need to invalidate - it was non-present before */
        update_mmu_cache(dst_vma, dst_addr, dst_pte);
        ret = 0;
out_unlock:
        pte_unmap_unlock(dst_pte, ptl);
out:
        return ret;
}

static int mfill_copy_folio_locked(struct folio *folio, unsigned long src_addr)
{
        void *kaddr;
        int ret;

        kaddr = kmap_local_folio(folio, 0);
        /*
         * The read mmap_lock is held here.  Despite the
         * mmap_lock being read recursive a deadlock is still
         * possible if a writer has taken a lock.  For example:
         *
         * process A thread 1 takes read lock on own mmap_lock
         * process A thread 2 calls mmap, blocks taking write lock
         * process B thread 1 takes page fault, read lock on own mmap lock
         * process B thread 2 calls mmap, blocks taking write lock
         * process A thread 1 blocks taking read lock on process B
         * process B thread 1 blocks taking read lock on process A
         *
         * Disable page faults to prevent potential deadlock
         * and retry the copy outside the mmap_lock.
         */
        pagefault_disable();
        ret = copy_from_user(kaddr, (const void __user *) src_addr,
                             PAGE_SIZE);
        pagefault_enable();
        kunmap_local(kaddr);

        if (ret)
                return -EFAULT;

        flush_dcache_folio(folio);
        return ret;
}

#define MFILL_RETRY_STATE_VMA_FLAGS \
        append_vma_flags(__VMA_UFFD_FLAGS, VMA_SHARED_BIT)

/*
 * VMA state saved before dropping the locks in mfill_copy_folio_retry().
 * Used to detect VMA replacement or incompatible changes after reacquiring the
 * locks.
 */
struct mfill_retry_state {
        const struct vm_uffd_ops *ops;
        struct file *file;
        vma_flags_t flags;
        pgoff_t pgoff;
};

static void mfill_retry_state_save(struct mfill_retry_state *s,
                                   struct vm_area_struct *vma)
{
        s->flags = vma_flags_and_mask(&vma->flags, MFILL_RETRY_STATE_VMA_FLAGS);
        s->ops = vma_uffd_ops(vma);
        s->pgoff = vma->vm_pgoff;

        if (vma->vm_file)
                s->file = get_file(vma->vm_file);
}

static bool mfill_retry_state_changed(struct mfill_retry_state *state,
                                      struct vm_area_struct *vma)
{
        vma_flags_t flags = vma_flags_and_mask(&vma->flags,
                                               MFILL_RETRY_STATE_VMA_FLAGS);

        /* Have any UFFD flags (missing, WP, minor) changed? */
        if (!vma_flags_same_pair(&state->flags, &flags))
                return true;

        /* VMA type or effective uffd_ops changed while the lock was dropped */
        if (state->ops != vma_uffd_ops(vma))
                return true;

        /* VMA was anonymous before; changed only if it no longer is */
        if (!state->file)
                return !vma_is_anonymous(vma);

        /* VMA was file backed, but file, inode or offset has changed */
        if (!vma->vm_file || vma->vm_file->f_inode != state->file->f_inode ||
            state->file != vma->vm_file || vma->vm_pgoff != state->pgoff)
                return true;

        return false;
}

static void mfill_retry_state_put(struct mfill_retry_state *s)
{
        if (s->file)
                fput(s->file);
}

DEFINE_FREE(retry_put, struct mfill_retry_state *,
            if (_T) mfill_retry_state_put(_T));

static int mfill_copy_folio_retry(struct mfill_state *mfill_state,
                                  struct folio *folio)
{
        struct mfill_retry_state retry_state = { 0 };
        struct mfill_retry_state *for_free __free(retry_put) = &retry_state;
        unsigned long src_addr = mfill_state->src_addr;
        void *kaddr;
        int err;

        mfill_retry_state_save(&retry_state, mfill_state->vma);

        /* retry copying with mm_lock dropped */
        mfill_put_vma(mfill_state);

        kaddr = kmap_local_folio(folio, 0);
        err = copy_from_user(kaddr, (const void __user *) src_addr, PAGE_SIZE);
        kunmap_local(kaddr);
        if (unlikely(err))
                return -EFAULT;

        flush_dcache_folio(folio);

        /* reget VMA and PMD, they could change underneath us */
        err = mfill_get_vma(mfill_state);
        if (err)
                return err;

        if (mfill_retry_state_changed(&retry_state, mfill_state->vma))
                return -EAGAIN;

        err = mfill_establish_pmd(mfill_state);
        if (err)
                return err;

        return 0;
}

static int __mfill_atomic_pte(struct mfill_state *state,
                              const struct vm_uffd_ops *ops)
{
        unsigned long dst_addr = state->dst_addr;
        unsigned long src_addr = state->src_addr;
        uffd_flags_t flags = state->flags;
        struct folio *folio;
        int ret;

        if (!ops) {
                VM_WARN_ONCE(1, "UFFDIO_COPY for unsupported VMA");
                return -EOPNOTSUPP;
        }

        folio = ops->alloc_folio(state->vma, state->dst_addr);
        if (!folio)
                return -ENOMEM;

        if (uffd_flags_mode_is(flags, MFILL_ATOMIC_COPY)) {
                ret = mfill_copy_folio_locked(folio, src_addr);
                /*
                 * Fallback to copy_from_user outside mmap_lock.
                 * If retry is successful, mfill_copy_folio_locked() returns
                 * with locks retaken by mfill_get_vma().
                 * If there was an error, we must mfill_put_vma() anyway and it
                 * will take care of unlocking if needed.
                 */
                if (unlikely(ret)) {
                        ret = mfill_copy_folio_retry(state, folio);
                        if (ret)
                                goto err_folio_put;
                }
        } else if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE)) {
                clear_user_highpage(&folio->page, state->dst_addr);
        } else {
                VM_WARN_ONCE(1, "Unknown UFFDIO operation, flags: %x", flags);
        }

        /*
         * The memory barrier inside __folio_mark_uptodate makes sure that
         * preceding stores to the page contents become visible before
         * the set_pte_at() write.
         */
        __folio_mark_uptodate(folio);

        if (ops->filemap_add) {
                ret = ops->filemap_add(folio, state->vma, state->dst_addr);
                if (ret)
                        goto err_folio_put;
        }

        ret = mfill_atomic_install_pte(state->pmd, state->vma, dst_addr,
                                       &folio->page, flags);
        if (ret)
                goto err_filemap_remove;

        return 0;

err_filemap_remove:
        if (ops->filemap_remove)
                ops->filemap_remove(folio, state->vma);
err_folio_put:
        folio_put(folio);
        return ret;
}

static int mfill_atomic_pte_copy(struct mfill_state *state)
{
        const struct vm_uffd_ops *ops = vma_uffd_ops(state->vma);

        /*
         * The normal page fault path for a MAP_PRIVATE mapping in a
         * file-backed VMA will invoke the fault, fill the hole in the file and
         * COW it right away. The result generates plain anonymous memory.
         * So when we are asked to fill a hole in a MAP_PRIVATE mapping, we'll
         * generate anonymous memory directly without actually filling the
         * hole. For the MAP_PRIVATE case the robustness check only happens in
         * the pagetable (to verify it's still none) and not in the page cache.
         */
        if (!(state->vma->vm_flags & VM_SHARED))
                ops = &anon_uffd_ops;

        return __mfill_atomic_pte(state, ops);
}

static int mfill_atomic_pte_zeroed_folio(struct mfill_state *state)
{
        const struct vm_uffd_ops *ops = vma_uffd_ops(state->vma);

        return __mfill_atomic_pte(state, ops);
}

static int mfill_atomic_pte_zeropage(struct mfill_state *state)
{
        struct vm_area_struct *dst_vma = state->vma;
        unsigned long dst_addr = state->dst_addr;
        pmd_t *dst_pmd = state->pmd;
        pte_t _dst_pte, *dst_pte;
        spinlock_t *ptl;
        int ret;

        if (mm_forbids_zeropage(dst_vma->vm_mm) ||
            (dst_vma->vm_flags & VM_SHARED))
                return mfill_atomic_pte_zeroed_folio(state);

        _dst_pte = pte_mkspecial(pfn_pte(zero_pfn(dst_addr),
                                         dst_vma->vm_page_prot));
        ret = -EAGAIN;
        dst_pte = pte_offset_map_lock(dst_vma->vm_mm, dst_pmd, dst_addr, &ptl);
        if (!dst_pte)
                goto out;
        if (mfill_file_over_size(dst_vma, dst_addr)) {
                ret = -EFAULT;
                goto out_unlock;
        }
        ret = -EEXIST;
        if (!pte_none(ptep_get(dst_pte)))
                goto out_unlock;
        set_pte_at(dst_vma->vm_mm, dst_addr, dst_pte, _dst_pte);
        /* No need to invalidate - it was non-present before */
        update_mmu_cache(dst_vma, dst_addr, dst_pte);
        ret = 0;
out_unlock:
        pte_unmap_unlock(dst_pte, ptl);
out:
        return ret;
}

/* Handles UFFDIO_CONTINUE for all shmem VMAs (shared or private). */
static int mfill_atomic_pte_continue(struct mfill_state *state)
{
        struct vm_area_struct *dst_vma = state->vma;
        const struct vm_uffd_ops *ops = vma_uffd_ops(dst_vma);
        unsigned long dst_addr = state->dst_addr;
        pgoff_t pgoff = linear_page_index(dst_vma, dst_addr);
        struct inode *inode = file_inode(dst_vma->vm_file);
        uffd_flags_t flags = state->flags;
        pmd_t *dst_pmd = state->pmd;
        struct folio *folio;
        struct page *page;
        int ret;

        if (!ops) {
                VM_WARN_ONCE(1, "UFFDIO_CONTINUE for unsupported VMA");
                return -EOPNOTSUPP;
        }

        folio = ops->get_folio_noalloc(inode, pgoff);
        /* Our caller expects us to return -EFAULT if we failed to find folio */
        if (IS_ERR_OR_NULL(folio))
                return -EFAULT;

        page = folio_file_page(folio, pgoff);
        if (PageHWPoison(page)) {
                ret = -EIO;
                goto out_release;
        }

        ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr,
                                       page, flags);
        if (ret)
                goto out_release;

        return 0;

out_release:
        folio_unlock(folio);
        folio_put(folio);
        return ret;
}

/* Handles UFFDIO_POISON for all non-hugetlb VMAs. */
static int mfill_atomic_pte_poison(struct mfill_state *state)
{
        struct vm_area_struct *dst_vma = state->vma;
        struct mm_struct *dst_mm = dst_vma->vm_mm;
        unsigned long dst_addr = state->dst_addr;
        pmd_t *dst_pmd = state->pmd;
        pte_t _dst_pte, *dst_pte;
        spinlock_t *ptl;
        int ret;

        _dst_pte = make_pte_marker(PTE_MARKER_POISONED);
        ret = -EAGAIN;
        dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
        if (!dst_pte)
                goto out;

        if (mfill_file_over_size(dst_vma, dst_addr)) {
                ret = -EFAULT;
                goto out_unlock;
        }

        ret = -EEXIST;
        /* Refuse to overwrite any PTE, even a PTE marker (e.g. UFFD WP). */
        if (!pte_none(ptep_get(dst_pte)))
                goto out_unlock;

        set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);

        /* No need to invalidate - it was non-present before */
        update_mmu_cache(dst_vma, dst_addr, dst_pte);
        ret = 0;
out_unlock:
        pte_unmap_unlock(dst_pte, ptl);
out:
        return ret;
}

#ifdef CONFIG_HUGETLB_PAGE
/*
 * mfill_atomic processing for HUGETLB vmas.  Note that this routine is
 * called with either vma-lock or mmap_lock held, it will release the lock
 * before returning.
 */
static __always_inline ssize_t mfill_atomic_hugetlb(
                                              struct userfaultfd_ctx *ctx,
                                              struct vm_area_struct *dst_vma,
                                              unsigned long dst_start,
                                              unsigned long src_start,
                                              unsigned long len,
                                              uffd_flags_t flags)
{
        struct mm_struct *dst_mm = dst_vma->vm_mm;
        ssize_t err;
        pte_t *dst_pte;
        unsigned long src_addr, dst_addr;
        long copied;
        struct folio *folio;
        unsigned long vma_hpagesize;
        pgoff_t idx;
        u32 hash;
        struct address_space *mapping;

        /*
         * There is no default zero huge page for all huge page sizes as
         * supported by hugetlb.  A PMD_SIZE huge pages may exist as used
         * by THP.  Since we can not reliably insert a zero page, this
         * feature is not supported.
         */
        if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE)) {
                up_read(&ctx->map_changing_lock);
                uffd_mfill_unlock(dst_vma);
                return -EINVAL;
        }

        src_addr = src_start;
        dst_addr = dst_start;
        copied = 0;
        folio = NULL;
        vma_hpagesize = vma_kernel_pagesize(dst_vma);

        /*
         * Validate alignment based on huge page size
         */
        err = -EINVAL;
        if (dst_start & (vma_hpagesize - 1) || len & (vma_hpagesize - 1))
                goto out_unlock;

retry:
        /*
         * On routine entry dst_vma is set.  If we had to drop mmap_lock and
         * retry, dst_vma will be set to NULL and we must lookup again.
         */
        if (!dst_vma) {
                dst_vma = uffd_mfill_lock(dst_mm, dst_start, len);
                if (IS_ERR(dst_vma)) {
                        err = PTR_ERR(dst_vma);
                        goto out;
                }

                err = -ENOENT;
                if (!is_vm_hugetlb_page(dst_vma))
                        goto out_unlock_vma;

                err = -EINVAL;
                if (vma_hpagesize != vma_kernel_pagesize(dst_vma))
                        goto out_unlock_vma;

                /*
                 * If memory mappings are changing because of non-cooperative
                 * operation (e.g. mremap) running in parallel, bail out and
                 * request the user to retry later
                 */
                down_read(&ctx->map_changing_lock);
                err = -EAGAIN;
                if (atomic_read(&ctx->mmap_changing))
                        goto out_unlock;
        }

        while (src_addr < src_start + len) {
                VM_WARN_ON_ONCE(dst_addr >= dst_start + len);

                /*
                 * Serialize via vma_lock and hugetlb_fault_mutex.
                 * vma_lock ensures the dst_pte remains valid even
                 * in the case of shared pmds.  fault mutex prevents
                 * races with other faulting threads.
                 */
                idx = hugetlb_linear_page_index(dst_vma, dst_addr);
                mapping = dst_vma->vm_file->f_mapping;
                hash = hugetlb_fault_mutex_hash(mapping, idx);
                mutex_lock(&hugetlb_fault_mutex_table[hash]);
                hugetlb_vma_lock_read(dst_vma);

                err = -ENOMEM;
                dst_pte = huge_pte_alloc(dst_mm, dst_vma, dst_addr, vma_hpagesize);
                if (!dst_pte) {
                        hugetlb_vma_unlock_read(dst_vma);
                        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
                        goto out_unlock;
                }

                if (!uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE)) {
                        const pte_t ptep = huge_ptep_get(dst_mm, dst_addr, dst_pte);

                        if (!huge_pte_none(ptep) && !pte_is_uffd_marker(ptep)) {
                                err = -EEXIST;
                                hugetlb_vma_unlock_read(dst_vma);
                                mutex_unlock(&hugetlb_fault_mutex_table[hash]);
                                goto out_unlock;
                        }
                }

                err = hugetlb_mfill_atomic_pte(dst_pte, dst_vma, dst_addr,
                                               src_addr, flags, &folio);

                hugetlb_vma_unlock_read(dst_vma);
                mutex_unlock(&hugetlb_fault_mutex_table[hash]);

                cond_resched();

                if (unlikely(err == -ENOENT)) {
                        up_read(&ctx->map_changing_lock);
                        uffd_mfill_unlock(dst_vma);
                        VM_WARN_ON_ONCE(!folio);

                        err = copy_folio_from_user(folio,
                                                   (const void __user *)src_addr, true);
                        if (unlikely(err)) {
                                err = -EFAULT;
                                goto out;
                        }

                        dst_vma = NULL;
                        goto retry;
                } else
                        VM_WARN_ON_ONCE(folio);

                if (!err) {
                        dst_addr += vma_hpagesize;
                        src_addr += vma_hpagesize;
                        copied += vma_hpagesize;

                        if (fatal_signal_pending(current))
                                err = -EINTR;
                }
                if (err)
                        break;
        }

out_unlock:
        up_read(&ctx->map_changing_lock);
out_unlock_vma:
        uffd_mfill_unlock(dst_vma);
out:
        if (folio)
                folio_put(folio);
        VM_WARN_ON_ONCE(copied < 0);
        VM_WARN_ON_ONCE(err > 0);
        VM_WARN_ON_ONCE(!copied && !err);
        return copied ? copied : err;
}
#else /* !CONFIG_HUGETLB_PAGE */
/* fail at build time if gcc attempts to use this */
extern ssize_t mfill_atomic_hugetlb(struct userfaultfd_ctx *ctx,
                                    struct vm_area_struct *dst_vma,
                                    unsigned long dst_start,
                                    unsigned long src_start,
                                    unsigned long len,
                                    uffd_flags_t flags);
#endif /* CONFIG_HUGETLB_PAGE */

static __always_inline ssize_t mfill_atomic_pte(struct mfill_state *state)
{
        uffd_flags_t flags = state->flags;

        if (uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE))
                return mfill_atomic_pte_continue(state);
        if (uffd_flags_mode_is(flags, MFILL_ATOMIC_POISON))
                return mfill_atomic_pte_poison(state);
        if (uffd_flags_mode_is(flags, MFILL_ATOMIC_COPY))
                return mfill_atomic_pte_copy(state);
        if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE))
                return mfill_atomic_pte_zeropage(state);

        VM_WARN_ONCE(1, "Unknown UFFDIO operation, flags: %x", flags);
        return -EOPNOTSUPP;
}

static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx,
                                            unsigned long dst_start,
                                            unsigned long src_start,
                                            unsigned long len,
                                            uffd_flags_t flags)
{
        struct mfill_state state = (struct mfill_state){
                .ctx = ctx,
                .dst_start = dst_start,
                .src_start = src_start,
                .flags = flags,
                .len = len,
                .src_addr = src_start,
                .dst_addr = dst_start,
        };
        long copied = 0;
        ssize_t err;

        /*
         * Sanitize the command parameters:
         */
        VM_WARN_ON_ONCE(dst_start & ~PAGE_MASK);
        VM_WARN_ON_ONCE(len & ~PAGE_MASK);

        /* Does the address range wrap, or is the span zero-sized? */
        VM_WARN_ON_ONCE(src_start + len <= src_start);
        VM_WARN_ON_ONCE(dst_start + len <= dst_start);

        err = mfill_get_vma(&state);
        if (err)
                goto out;

        /*
         * If this is a HUGETLB vma, pass off to appropriate routine
         */
        if (is_vm_hugetlb_page(state.vma))
                return  mfill_atomic_hugetlb(ctx, state.vma, dst_start,
                                             src_start, len, flags);

        while (state.src_addr < src_start + len) {
                VM_WARN_ON_ONCE(state.dst_addr >= dst_start + len);

                err = mfill_establish_pmd(&state);
                if (err)
                        break;

                /*
                 * For shmem mappings, khugepaged is allowed to remove page
                 * tables under us; pte_offset_map_lock() will deal with that.
                 */

                err = mfill_atomic_pte(&state);
                cond_resched();

                if (!err) {
                        state.dst_addr += PAGE_SIZE;
                        state.src_addr += PAGE_SIZE;
                        copied += PAGE_SIZE;

                        if (fatal_signal_pending(current))
                                err = -EINTR;
                }
                if (err)
                        break;
        }

        mfill_put_vma(&state);
out:
        VM_WARN_ON_ONCE(copied < 0);
        VM_WARN_ON_ONCE(err > 0);
        VM_WARN_ON_ONCE(!copied && !err);
        return copied ? copied : err;
}

static ssize_t mfill_atomic_copy(struct userfaultfd_ctx *ctx, unsigned long dst_start,
                          unsigned long src_start, unsigned long len,
                          uffd_flags_t flags)
{
        return mfill_atomic(ctx, dst_start, src_start, len,
                            uffd_flags_set_mode(flags, MFILL_ATOMIC_COPY));
}

static ssize_t mfill_atomic_zeropage(struct userfaultfd_ctx *ctx,
                              unsigned long start,
                              unsigned long len)
{
        return mfill_atomic(ctx, start, 0, len,
                            uffd_flags_set_mode(0, MFILL_ATOMIC_ZEROPAGE));
}

static ssize_t mfill_atomic_continue(struct userfaultfd_ctx *ctx, unsigned long start,
                              unsigned long len, uffd_flags_t flags)
{

        /*
         * A caller might reasonably assume that UFFDIO_CONTINUE contains an
         * smp_wmb() to ensure that any writes to the about-to-be-mapped page by
         * the thread doing the UFFDIO_CONTINUE are guaranteed to be visible to
         * subsequent loads from the page through the newly mapped address range.
         */
        smp_wmb();

        return mfill_atomic(ctx, start, 0, len,
                            uffd_flags_set_mode(flags, MFILL_ATOMIC_CONTINUE));
}

static ssize_t mfill_atomic_poison(struct userfaultfd_ctx *ctx, unsigned long start,
                            unsigned long len, uffd_flags_t flags)
{
        return mfill_atomic(ctx, start, 0, len,
                            uffd_flags_set_mode(flags, MFILL_ATOMIC_POISON));
}

long uffd_wp_range(struct vm_area_struct *dst_vma,
                   unsigned long start, unsigned long len, bool enable_wp)
{
        unsigned int mm_cp_flags;
        struct mmu_gather tlb;
        long ret;

        VM_WARN_ONCE(start < dst_vma->vm_start || start + len > dst_vma->vm_end,
                        "The address range exceeds VMA boundary.\n");
        if (enable_wp)
                mm_cp_flags = MM_CP_UFFD_WP;
        else
                mm_cp_flags = MM_CP_UFFD_WP_RESOLVE;

        /*
         * vma->vm_page_prot already reflects that uffd-wp is enabled for this
         * VMA (see userfaultfd_set_vm_flags()) and that all PTEs are supposed
         * to be write-protected as default whenever protection changes.
         * Try upgrading write permissions manually.
         */
        if (!enable_wp && vma_wants_manual_pte_write_upgrade(dst_vma))
                mm_cp_flags |= MM_CP_TRY_CHANGE_WRITABLE;
        tlb_gather_mmu(&tlb, dst_vma->vm_mm);
        ret = change_protection(&tlb, dst_vma, start, start + len, mm_cp_flags);
        tlb_finish_mmu(&tlb);

        return ret;
}

static int mwriteprotect_range(struct userfaultfd_ctx *ctx, unsigned long start,
                        unsigned long len, bool enable_wp)
{
        struct mm_struct *dst_mm = ctx->mm;
        unsigned long end = start + len;
        unsigned long _start, _end;
        struct vm_area_struct *dst_vma;
        unsigned long page_mask;
        long err;
        VMA_ITERATOR(vmi, dst_mm, start);

        /*
         * Sanitize the command parameters:
         */
        VM_WARN_ON_ONCE(start & ~PAGE_MASK);
        VM_WARN_ON_ONCE(len & ~PAGE_MASK);

        /* Does the address range wrap, or is the span zero-sized? */
        VM_WARN_ON_ONCE(start + len <= start);

        mmap_read_lock(dst_mm);

        /*
         * If memory mappings are changing because of non-cooperative
         * operation (e.g. mremap) running in parallel, bail out and
         * request the user to retry later
         */
        down_read(&ctx->map_changing_lock);
        err = -EAGAIN;
        if (atomic_read(&ctx->mmap_changing))
                goto out_unlock;

        err = -ENOENT;
        for_each_vma_range(vmi, dst_vma, end) {

                if (!userfaultfd_wp(dst_vma)) {
                        err = -ENOENT;
                        break;
                }

                if (is_vm_hugetlb_page(dst_vma)) {
                        err = -EINVAL;
                        page_mask = vma_kernel_pagesize(dst_vma) - 1;
                        if ((start & page_mask) || (len & page_mask))
                                break;
                }

                _start = max(dst_vma->vm_start, start);
                _end = min(dst_vma->vm_end, end);

                err = uffd_wp_range(dst_vma, _start, _end - _start, enable_wp);

                /* Return 0 on success, <0 on failures */
                if (err < 0)
                        break;
                err = 0;
        }
out_unlock:
        up_read(&ctx->map_changing_lock);
        mmap_read_unlock(dst_mm);
        return err;
}


void double_pt_lock(spinlock_t *ptl1,
                    spinlock_t *ptl2)
        __acquires(ptl1)
        __acquires(ptl2)
{
        if (ptl1 > ptl2)
                swap(ptl1, ptl2);
        /* lock in virtual address order to avoid lock inversion */
        spin_lock(ptl1);
        if (ptl1 != ptl2)
                spin_lock_nested(ptl2, SINGLE_DEPTH_NESTING);
        else
                __acquire(ptl2);
}

void double_pt_unlock(spinlock_t *ptl1,
                      spinlock_t *ptl2)
        __releases(ptl1)
        __releases(ptl2)
{
        spin_unlock(ptl1);
        if (ptl1 != ptl2)
                spin_unlock(ptl2);
        else
                __release(ptl2);
}

static inline bool is_pte_pages_stable(pte_t *dst_pte, pte_t *src_pte,
                                       pte_t orig_dst_pte, pte_t orig_src_pte,
                                       pmd_t *dst_pmd, pmd_t dst_pmdval)
{
        return pte_same(ptep_get(src_pte), orig_src_pte) &&
               pte_same(ptep_get(dst_pte), orig_dst_pte) &&
               pmd_same(dst_pmdval, pmdp_get_lockless(dst_pmd));
}

/*
 * Checks if the two ptes and the corresponding folio are eligible for batched
 * move. If so, then returns pointer to the locked folio. Otherwise, returns NULL.
 *
 * NOTE: folio's reference is not required as the whole operation is within
 * PTL's critical section.
 */
static struct folio *check_ptes_for_batched_move(struct vm_area_struct *src_vma,
                                                 unsigned long src_addr,
                                                 pte_t *src_pte, pte_t *dst_pte)
{
        pte_t orig_dst_pte, orig_src_pte;
        struct folio *folio;

        orig_dst_pte = ptep_get(dst_pte);
        if (!pte_none(orig_dst_pte))
                return NULL;

        orig_src_pte = ptep_get(src_pte);
        if (!pte_present(orig_src_pte) || is_zero_pfn(pte_pfn(orig_src_pte)))
                return NULL;

        folio = vm_normal_folio(src_vma, src_addr, orig_src_pte);
        if (!folio || !folio_trylock(folio))
                return NULL;
        if (!PageAnonExclusive(&folio->page) || folio_test_large(folio)) {
                folio_unlock(folio);
                return NULL;
        }
        return folio;
}

/*
 * Moves src folios to dst in a batch as long as they are not large, and can
 * successfully take the lock via folio_trylock().
 */
static long move_present_ptes(struct mm_struct *mm,
                              struct vm_area_struct *dst_vma,
                              struct vm_area_struct *src_vma,
                              unsigned long dst_addr, unsigned long src_addr,
                              pte_t *dst_pte, pte_t *src_pte,
                              pte_t orig_dst_pte, pte_t orig_src_pte,
                              pmd_t *dst_pmd, pmd_t dst_pmdval,
                              spinlock_t *dst_ptl, spinlock_t *src_ptl,
                              struct folio **first_src_folio, unsigned long len)
{
        int err = 0;
        struct folio *src_folio = *first_src_folio;
        unsigned long src_start = src_addr;
        unsigned long src_end;

        len = pmd_addr_end(dst_addr, dst_addr + len) - dst_addr;
        src_end = pmd_addr_end(src_addr, src_addr + len);
        flush_cache_range(src_vma, src_addr, src_end);
        double_pt_lock(dst_ptl, src_ptl);

        if (!is_pte_pages_stable(dst_pte, src_pte, orig_dst_pte, orig_src_pte,
                                 dst_pmd, dst_pmdval)) {
                err = -EAGAIN;
                goto out;
        }
        if (folio_test_large(src_folio) ||
            folio_maybe_dma_pinned(src_folio) ||
            !PageAnonExclusive(&src_folio->page)) {
                err = -EBUSY;
                goto out;
        }
        /* It's safe to drop the reference now as the page-table is holding one. */
        folio_put(*first_src_folio);
        *first_src_folio = NULL;
        lazy_mmu_mode_enable();

        while (true) {
                orig_src_pte = ptep_get_and_clear(mm, src_addr, src_pte);
                /* Folio got pinned from under us. Put it back and fail the move. */
                if (folio_maybe_dma_pinned(src_folio)) {
                        set_pte_at(mm, src_addr, src_pte, orig_src_pte);
                        err = -EBUSY;
                        break;
                }

                folio_move_anon_rmap(src_folio, dst_vma);
                src_folio->index = linear_page_index(dst_vma, dst_addr);

                orig_dst_pte = folio_mk_pte(src_folio, dst_vma->vm_page_prot);
                /* Set soft dirty bit so userspace can notice the pte was moved */
                if (pgtable_supports_soft_dirty())
                        orig_dst_pte = pte_mksoft_dirty(orig_dst_pte);
                if (pte_dirty(orig_src_pte))
                        orig_dst_pte = pte_mkdirty(orig_dst_pte);
                orig_dst_pte = pte_mkwrite(orig_dst_pte, dst_vma);
                set_pte_at(mm, dst_addr, dst_pte, orig_dst_pte);

                src_addr += PAGE_SIZE;
                if (src_addr == src_end)
                        break;
                dst_addr += PAGE_SIZE;
                dst_pte++;
                src_pte++;

                folio_unlock(src_folio);
                src_folio = check_ptes_for_batched_move(src_vma, src_addr,
                                                        src_pte, dst_pte);
                if (!src_folio)
                        break;
        }

        lazy_mmu_mode_disable();
        if (src_addr > src_start)
                flush_tlb_range(src_vma, src_start, src_addr);

        if (src_folio)
                folio_unlock(src_folio);
out:
        double_pt_unlock(dst_ptl, src_ptl);
        return src_addr > src_start ? src_addr - src_start : err;
}

static int move_swap_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma,
                         unsigned long dst_addr, unsigned long src_addr,
                         pte_t *dst_pte, pte_t *src_pte,
                         pte_t orig_dst_pte, pte_t orig_src_pte,
                         pmd_t *dst_pmd, pmd_t dst_pmdval,
                         spinlock_t *dst_ptl, spinlock_t *src_ptl,
                         struct folio *src_folio,
                         struct swap_info_struct *si, swp_entry_t entry)
{
        /*
         * Check if the folio still belongs to the target swap entry after
         * acquiring the lock. Folio can be freed in the swap cache while
         * not locked.
         */
        if (src_folio && unlikely(!folio_test_swapcache(src_folio) ||
                                  entry.val != src_folio->swap.val))
                return -EAGAIN;

        double_pt_lock(dst_ptl, src_ptl);

        if (!is_pte_pages_stable(dst_pte, src_pte, orig_dst_pte, orig_src_pte,
                                 dst_pmd, dst_pmdval)) {
                double_pt_unlock(dst_ptl, src_ptl);
                return -EAGAIN;
        }

        /*
         * The src_folio resides in the swapcache, requiring an update to its
         * index and mapping to align with the dst_vma, where a swap-in may
         * occur and hit the swapcache after moving the PTE.
         */
        if (src_folio) {
                folio_move_anon_rmap(src_folio, dst_vma);
                src_folio->index = linear_page_index(dst_vma, dst_addr);
        } else {
                /*
                 * Check if the swap entry is cached after acquiring the src_pte
                 * lock. Otherwise, we might miss a newly loaded swap cache folio.
                 *
                 * We are trying to catch newly added swap cache, the only possible case is
                 * when a folio is swapped in and out again staying in swap cache, using the
                 * same entry before the PTE check above. The PTL is acquired and released
                 * twice, each time after updating the swap table. So holding
                 * the PTL here ensures we see the updated value.
                 */
                if (swap_cache_has_folio(entry)) {
                        double_pt_unlock(dst_ptl, src_ptl);
                        return -EAGAIN;
                }
        }

        orig_src_pte = ptep_get_and_clear(mm, src_addr, src_pte);
        if (pgtable_supports_soft_dirty())
                orig_src_pte = pte_swp_mksoft_dirty(orig_src_pte);
        set_pte_at(mm, dst_addr, dst_pte, orig_src_pte);
        double_pt_unlock(dst_ptl, src_ptl);

        return PAGE_SIZE;
}

static int move_zeropage_pte(struct mm_struct *mm,
                             struct vm_area_struct *dst_vma,
                             struct vm_area_struct *src_vma,
                             unsigned long dst_addr, unsigned long src_addr,
                             pte_t *dst_pte, pte_t *src_pte,
                             pte_t orig_dst_pte, pte_t orig_src_pte,
                             pmd_t *dst_pmd, pmd_t dst_pmdval,
                             spinlock_t *dst_ptl, spinlock_t *src_ptl)
{
        pte_t zero_pte;

        double_pt_lock(dst_ptl, src_ptl);
        if (!is_pte_pages_stable(dst_pte, src_pte, orig_dst_pte, orig_src_pte,
                                 dst_pmd, dst_pmdval)) {
                double_pt_unlock(dst_ptl, src_ptl);
                return -EAGAIN;
        }

        zero_pte = pte_mkspecial(pfn_pte(zero_pfn(dst_addr),
                                         dst_vma->vm_page_prot));
        ptep_clear_flush(src_vma, src_addr, src_pte);
        set_pte_at(mm, dst_addr, dst_pte, zero_pte);
        double_pt_unlock(dst_ptl, src_ptl);

        return PAGE_SIZE;
}


/*
 * The mmap_lock for reading is held by the caller. Just move the page(s)
 * from src_pmd to dst_pmd if possible, and return number of bytes moved.
 * On failure, an error code is returned.
 */
static long move_pages_ptes(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd,
                            struct vm_area_struct *dst_vma,
                            struct vm_area_struct *src_vma,
                            unsigned long dst_addr, unsigned long src_addr,
                            unsigned long len, __u64 mode)
{
        struct swap_info_struct *si = NULL;
        pte_t orig_src_pte, orig_dst_pte;
        pte_t src_folio_pte;
        spinlock_t *src_ptl, *dst_ptl;
        pte_t *src_pte = NULL;
        pte_t *dst_pte = NULL;
        pmd_t dummy_pmdval;
        pmd_t dst_pmdval;
        struct folio *src_folio = NULL;
        struct mmu_notifier_range range;
        long ret = 0;

        mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm,
                                src_addr, src_addr + len);
        mmu_notifier_invalidate_range_start(&range);
retry:
        /*
         * Use the maywrite version to indicate that dst_pte will be modified,
         * since dst_pte needs to be none, the subsequent pte_same() check
         * cannot prevent the dst_pte page from being freed concurrently, so we
         * also need to obtain dst_pmdval and recheck pmd_same() later.
         */
        dst_pte = pte_offset_map_rw_nolock(mm, dst_pmd, dst_addr, &dst_pmdval,
                                           &dst_ptl);

        /* Retry if a huge pmd materialized from under us */
        if (unlikely(!dst_pte)) {
                ret = -EAGAIN;
                goto out;
        }

        /*
         * Unlike dst_pte, the subsequent pte_same() check can ensure the
         * stability of the src_pte page, so there is no need to get pmdval,
         * just pass a dummy variable to it.
         */
        src_pte = pte_offset_map_rw_nolock(mm, src_pmd, src_addr, &dummy_pmdval,
                                           &src_ptl);

        /*
         * We held the mmap_lock for reading so MADV_DONTNEED
         * can zap transparent huge pages under us, or the
         * transparent huge page fault can establish new
         * transparent huge pages under us.
         */
        if (unlikely(!src_pte)) {
                ret = -EAGAIN;
                goto out;
        }

        /* Sanity checks before the operation */
        if (pmd_none(*dst_pmd) || pmd_none(*src_pmd) ||
            pmd_trans_huge(*dst_pmd) || pmd_trans_huge(*src_pmd)) {
                ret = -EINVAL;
                goto out;
        }

        spin_lock(dst_ptl);
        orig_dst_pte = ptep_get(dst_pte);
        spin_unlock(dst_ptl);
        if (!pte_none(orig_dst_pte)) {
                ret = -EEXIST;
                goto out;
        }

        spin_lock(src_ptl);
        orig_src_pte = ptep_get(src_pte);
        spin_unlock(src_ptl);
        if (pte_none(orig_src_pte)) {
                if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES))
                        ret = -ENOENT;
                else /* nothing to do to move a hole */
                        ret = PAGE_SIZE;
                goto out;
        }

        /* If PTE changed after we locked the folio then start over */
        if (src_folio && unlikely(!pte_same(src_folio_pte, orig_src_pte))) {
                ret = -EAGAIN;
                goto out;
        }

        if (pte_present(orig_src_pte)) {
                if (is_zero_pfn(pte_pfn(orig_src_pte))) {
                        ret = move_zeropage_pte(mm, dst_vma, src_vma,
                                               dst_addr, src_addr, dst_pte, src_pte,
                                               orig_dst_pte, orig_src_pte,
                                               dst_pmd, dst_pmdval, dst_ptl, src_ptl);
                        goto out;
                }

                /*
                 * Pin and lock source folio. Since we are in RCU read section,
                 * we can't block, so on contention have to unmap the ptes,
                 * obtain the lock and retry.
                 */
                if (!src_folio) {
                        struct folio *folio;
                        bool locked;

                        /*
                         * Pin the page while holding the lock to be sure the
                         * page isn't freed under us
                         */
                        spin_lock(src_ptl);
                        if (!pte_same(orig_src_pte, ptep_get(src_pte))) {
                                spin_unlock(src_ptl);
                                ret = -EAGAIN;
                                goto out;
                        }

                        folio = vm_normal_folio(src_vma, src_addr, orig_src_pte);
                        if (!folio || !PageAnonExclusive(&folio->page)) {
                                spin_unlock(src_ptl);
                                ret = -EBUSY;
                                goto out;
                        }

                        locked = folio_trylock(folio);
                        /*
                         * We avoid waiting for folio lock with a raised
                         * refcount for large folios because extra refcounts
                         * will result in split_folio() failing later and
                         * retrying.  If multiple tasks are trying to move a
                         * large folio we can end up livelocking.
                         */
                        if (!locked && folio_test_large(folio)) {
                                spin_unlock(src_ptl);
                                ret = -EAGAIN;
                                goto out;
                        }

                        folio_get(folio);
                        src_folio = folio;
                        src_folio_pte = orig_src_pte;
                        spin_unlock(src_ptl);

                        if (!locked) {
                                pte_unmap(src_pte);
                                pte_unmap(dst_pte);
                                src_pte = dst_pte = NULL;
                                /* now we can block and wait */
                                folio_lock(src_folio);
                                goto retry;
                        }

                        if (WARN_ON_ONCE(!folio_test_anon(src_folio))) {
                                ret = -EBUSY;
                                goto out;
                        }
                }

                /* at this point we have src_folio locked */
                if (folio_test_large(src_folio)) {
                        /* split_folio() can block */
                        pte_unmap(src_pte);
                        pte_unmap(dst_pte);
                        src_pte = dst_pte = NULL;
                        ret = split_folio(src_folio);
                        if (ret)
                                goto out;
                        /* have to reacquire the folio after it got split */
                        folio_unlock(src_folio);
                        folio_put(src_folio);
                        src_folio = NULL;
                        goto retry;
                }

                ret = move_present_ptes(mm, dst_vma, src_vma,
                                        dst_addr, src_addr, dst_pte, src_pte,
                                        orig_dst_pte, orig_src_pte, dst_pmd,
                                        dst_pmdval, dst_ptl, src_ptl, &src_folio,
                                        len);
        } else { /* !pte_present() */
                struct folio *folio = NULL;
                const softleaf_t entry = softleaf_from_pte(orig_src_pte);

                if (softleaf_is_migration(entry)) {
                        pte_unmap(src_pte);
                        pte_unmap(dst_pte);
                        src_pte = dst_pte = NULL;
                        migration_entry_wait(mm, src_pmd, src_addr);

                        ret = -EAGAIN;
                        goto out;
                } else if (!softleaf_is_swap(entry)) {
                        ret = -EFAULT;
                        goto out;
                }

                if (!pte_swp_exclusive(orig_src_pte)) {
                        ret = -EBUSY;
                        goto out;
                }

                si = get_swap_device(entry);
                if (unlikely(!si)) {
                        ret = -EAGAIN;
                        goto out;
                }
                /*
                 * Verify the existence of the swapcache. If present, the folio's
                 * index and mapping must be updated even when the PTE is a swap
                 * entry. The anon_vma lock is not taken during this process since
                 * the folio has already been unmapped, and the swap entry is
                 * exclusive, preventing rmap walks.
                 *
                 * For large folios, return -EBUSY immediately, as split_folio()
                 * also returns -EBUSY when attempting to split unmapped large
                 * folios in the swapcache. This issue needs to be resolved
                 * separately to allow proper handling.
                 */
                if (!src_folio)
                        folio = swap_cache_get_folio(entry);
                if (folio) {
                        if (folio_test_large(folio)) {
                                ret = -EBUSY;
                                folio_put(folio);
                                goto out;
                        }
                        src_folio = folio;
                        src_folio_pte = orig_src_pte;
                        if (!folio_trylock(src_folio)) {
                                pte_unmap(src_pte);
                                pte_unmap(dst_pte);
                                src_pte = dst_pte = NULL;
                                put_swap_device(si);
                                si = NULL;
                                /* now we can block and wait */
                                folio_lock(src_folio);
                                goto retry;
                        }
                }
                ret = move_swap_pte(mm, dst_vma, dst_addr, src_addr, dst_pte, src_pte,
                                orig_dst_pte, orig_src_pte, dst_pmd, dst_pmdval,
                                dst_ptl, src_ptl, src_folio, si, entry);
        }

out:
        if (src_folio) {
                folio_unlock(src_folio);
                folio_put(src_folio);
        }
        /*
         * Unmap in reverse order (LIFO) to maintain proper kmap_local
         * index ordering when CONFIG_HIGHPTE is enabled. We mapped dst_pte
         * first, then src_pte, so we must unmap src_pte first, then dst_pte.
         */
        if (src_pte)
                pte_unmap(src_pte);
        if (dst_pte)
                pte_unmap(dst_pte);
        mmu_notifier_invalidate_range_end(&range);
        if (si)
                put_swap_device(si);

        return ret;
}

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
static inline bool move_splits_huge_pmd(unsigned long dst_addr,
                                        unsigned long src_addr,
                                        unsigned long src_end)
{
        return (src_addr & ~HPAGE_PMD_MASK) || (dst_addr & ~HPAGE_PMD_MASK) ||
                src_end - src_addr < HPAGE_PMD_SIZE;
}
#else
static inline bool move_splits_huge_pmd(unsigned long dst_addr,
                                        unsigned long src_addr,
                                        unsigned long src_end)
{
        /* This is unreachable anyway, just to avoid warnings when HPAGE_PMD_SIZE==0 */
        return false;
}
#endif

static inline bool vma_move_compatible(struct vm_area_struct *vma)
{
        return !(vma->vm_flags & (VM_PFNMAP | VM_IO |  VM_HUGETLB |
                                  VM_MIXEDMAP | VM_SHADOW_STACK));
}

static int validate_move_areas(struct userfaultfd_ctx *ctx,
                               struct vm_area_struct *src_vma,
                               struct vm_area_struct *dst_vma)
{
        /* Only allow moving if both have the same access and protection */
        if ((src_vma->vm_flags & VM_ACCESS_FLAGS) != (dst_vma->vm_flags & VM_ACCESS_FLAGS) ||
            pgprot_val(src_vma->vm_page_prot) != pgprot_val(dst_vma->vm_page_prot))
                return -EINVAL;

        /* Only allow moving if both are mlocked or both aren't */
        if ((src_vma->vm_flags & VM_LOCKED) != (dst_vma->vm_flags & VM_LOCKED))
                return -EINVAL;

        /*
         * For now, we keep it simple and only move between writable VMAs.
         * Access flags are equal, therefore checking only the source is enough.
         */
        if (!(src_vma->vm_flags & VM_WRITE))
                return -EINVAL;

        /* Check if vma flags indicate content which can be moved */
        if (!vma_move_compatible(src_vma) || !vma_move_compatible(dst_vma))
                return -EINVAL;

        /* Ensure dst_vma is registered in uffd we are operating on */
        if (!dst_vma->vm_userfaultfd_ctx.ctx ||
            dst_vma->vm_userfaultfd_ctx.ctx != ctx)
                return -EINVAL;

        /* Only allow moving across anonymous vmas */
        if (!vma_is_anonymous(src_vma) || !vma_is_anonymous(dst_vma))
                return -EINVAL;

        return 0;
}

static __always_inline
int find_vmas_mm_locked(struct mm_struct *mm,
                        unsigned long dst_start,
                        unsigned long src_start,
                        struct vm_area_struct **dst_vmap,
                        struct vm_area_struct **src_vmap)
{
        struct vm_area_struct *vma;

        mmap_assert_locked(mm);
        vma = find_vma_and_prepare_anon(mm, dst_start);
        if (IS_ERR(vma))
                return PTR_ERR(vma);

        *dst_vmap = vma;
        /* Skip finding src_vma if src_start is in dst_vma */
        if (src_start >= vma->vm_start && src_start < vma->vm_end)
                goto out_success;

        vma = vma_lookup(mm, src_start);
        if (!vma)
                return -ENOENT;
out_success:
        *src_vmap = vma;
        return 0;
}

#ifdef CONFIG_PER_VMA_LOCK
static int uffd_move_lock(struct mm_struct *mm,
                          unsigned long dst_start,
                          unsigned long src_start,
                          struct vm_area_struct **dst_vmap,
                          struct vm_area_struct **src_vmap)
{
        struct vm_area_struct *vma;
        int err;

        vma = uffd_lock_vma(mm, dst_start);
        if (IS_ERR(vma))
                return PTR_ERR(vma);

        *dst_vmap = vma;
        /*
         * Skip finding src_vma if src_start is in dst_vma. This also ensures
         * that we don't lock the same vma twice.
         */
        if (src_start >= vma->vm_start && src_start < vma->vm_end) {
                *src_vmap = vma;
                return 0;
        }

        /*
         * Using uffd_lock_vma() to get src_vma can lead to following deadlock:
         *
         * Thread1                              Thread2
         * -------                              -------
         * vma_start_read(dst_vma)
         *                                      mmap_write_lock(mm)
         *                                      vma_start_write(src_vma)
         * vma_start_read(src_vma)
         * mmap_read_lock(mm)
         *                                      vma_start_write(dst_vma)
         */
        *src_vmap = lock_vma_under_rcu(mm, src_start);
        if (likely(*src_vmap))
                return 0;

        /* Undo any locking and retry in mmap_lock critical section */
        vma_end_read(*dst_vmap);

        mmap_read_lock(mm);
        err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap);
        if (err)
                goto out;

        if (!vma_start_read_locked(*dst_vmap)) {
                err = -EAGAIN;
                goto out;
        }

        /* Nothing further to do if both vmas are locked. */
        if (*dst_vmap == *src_vmap)
                goto out;

        if (!vma_start_read_locked_nested(*src_vmap, SINGLE_DEPTH_NESTING)) {
                /* Undo dst_vmap locking if src_vmap failed to lock */
                vma_end_read(*dst_vmap);
                err = -EAGAIN;
        }
out:
        mmap_read_unlock(mm);
        return err;
}

static void uffd_move_unlock(struct vm_area_struct *dst_vma,
                             struct vm_area_struct *src_vma)
{
        vma_end_read(src_vma);
        if (src_vma != dst_vma)
                vma_end_read(dst_vma);
}

#else

static int uffd_move_lock(struct mm_struct *mm,
                          unsigned long dst_start,
                          unsigned long src_start,
                          struct vm_area_struct **dst_vmap,
                          struct vm_area_struct **src_vmap)
{
        int err;

        mmap_read_lock(mm);
        err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap);
        if (err)
                mmap_read_unlock(mm);
        return err;
}

static void uffd_move_unlock(struct vm_area_struct *dst_vma,
                             struct vm_area_struct *src_vma)
{
        mmap_assert_locked(src_vma->vm_mm);
        mmap_read_unlock(dst_vma->vm_mm);
}
#endif

/**
 * move_pages - move arbitrary anonymous pages of an existing vma
 * @ctx: pointer to the userfaultfd context
 * @dst_start: start of the destination virtual memory range
 * @src_start: start of the source virtual memory range
 * @len: length of the virtual memory range
 * @mode: flags from uffdio_move.mode
 *
 * It will either use the mmap_lock in read mode or per-vma locks
 *
 * move_pages() remaps arbitrary anonymous pages atomically in zero
 * copy. It only works on non shared anonymous pages because those can
 * be relocated without generating non linear anon_vmas in the rmap
 * code.
 *
 * It provides a zero copy mechanism to handle userspace page faults.
 * The source vma pages should have mapcount == 1, which can be
 * enforced by using madvise(MADV_DONTFORK) on src vma.
 *
 * The thread receiving the page during the userland page fault
 * will receive the faulting page in the source vma through the network,
 * storage or any other I/O device (MADV_DONTFORK in the source vma
 * avoids move_pages() to fail with -EBUSY if the process forks before
 * move_pages() is called), then it will call move_pages() to map the
 * page in the faulting address in the destination vma.
 *
 * This userfaultfd command works purely via pagetables, so it's the
 * most efficient way to move physical non shared anonymous pages
 * across different virtual addresses. Unlike mremap()/mmap()/munmap()
 * it does not create any new vmas. The mapping in the destination
 * address is atomic.
 *
 * It only works if the vma protection bits are identical from the
 * source and destination vma.
 *
 * It can remap non shared anonymous pages within the same vma too.
 *
 * If the source virtual memory range has any unmapped holes, or if
 * the destination virtual memory range is not a whole unmapped hole,
 * move_pages() will fail respectively with -ENOENT or -EEXIST. This
 * provides a very strict behavior to avoid any chance of memory
 * corruption going unnoticed if there are userland race conditions.
 * Only one thread should resolve the userland page fault at any given
 * time for any given faulting address. This means that if two threads
 * try to both call move_pages() on the same destination address at the
 * same time, the second thread will get an explicit error from this
 * command.
 *
 * The command retval will return "len" is successful. The command
 * however can be interrupted by fatal signals or errors. If
 * interrupted it will return the number of bytes successfully
 * remapped before the interruption if any, or the negative error if
 * none. It will never return zero. Either it will return an error or
 * an amount of bytes successfully moved. If the retval reports a
 * "short" remap, the move_pages() command should be repeated by
 * userland with src+retval, dst+reval, len-retval if it wants to know
 * about the error that interrupted it.
 *
 * The UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES flag can be specified to
 * prevent -ENOENT errors to materialize if there are holes in the
 * source virtual range that is being remapped. The holes will be
 * accounted as successfully remapped in the retval of the
 * command. This is mostly useful to remap hugepage naturally aligned
 * virtual regions without knowing if there are transparent hugepage
 * in the regions or not, but preventing the risk of having to split
 * the hugepmd during the remap.
 */
static ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start,
                   unsigned long src_start, unsigned long len, __u64 mode)
{
        struct mm_struct *mm = ctx->mm;
        struct vm_area_struct *src_vma, *dst_vma;
        unsigned long src_addr, dst_addr, src_end;
        pmd_t *src_pmd, *dst_pmd;
        long err = -EINVAL;
        ssize_t moved = 0;

        /* Sanitize the command parameters. */
        VM_WARN_ON_ONCE(src_start & ~PAGE_MASK);
        VM_WARN_ON_ONCE(dst_start & ~PAGE_MASK);
        VM_WARN_ON_ONCE(len & ~PAGE_MASK);

        /* Does the address range wrap, or is the span zero-sized? */
        VM_WARN_ON_ONCE(src_start + len < src_start);
        VM_WARN_ON_ONCE(dst_start + len < dst_start);

        err = uffd_move_lock(mm, dst_start, src_start, &dst_vma, &src_vma);
        if (err)
                goto out;

        /* Re-check after taking map_changing_lock */
        err = -EAGAIN;
        down_read(&ctx->map_changing_lock);
        if (likely(atomic_read(&ctx->mmap_changing)))
                goto out_unlock;
        /*
         * Make sure the vma is not shared, that the src and dst remap
         * ranges are both valid and fully within a single existing
         * vma.
         */
        err = -EINVAL;
        if (src_vma->vm_flags & VM_SHARED)
                goto out_unlock;
        if (src_start + len > src_vma->vm_end)
                goto out_unlock;

        if (dst_vma->vm_flags & VM_SHARED)
                goto out_unlock;
        if (dst_start + len > dst_vma->vm_end)
                goto out_unlock;

        err = validate_move_areas(ctx, src_vma, dst_vma);
        if (err)
                goto out_unlock;

        for (src_addr = src_start, dst_addr = dst_start, src_end = src_start + len;
             src_addr < src_end;) {
                spinlock_t *ptl;
                pmd_t dst_pmdval;
                unsigned long step_size;

                /*
                 * Below works because anonymous area would not have a
                 * transparent huge PUD. If file-backed support is added,
                 * that case would need to be handled here.
                 */
                src_pmd = mm_find_pmd(mm, src_addr);
                if (unlikely(!src_pmd)) {
                        if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) {
                                err = -ENOENT;
                                break;
                        }
                        src_pmd = mm_alloc_pmd(mm, src_addr);
                        if (unlikely(!src_pmd)) {
                                err = -ENOMEM;
                                break;
                        }
                }
                dst_pmd = mm_alloc_pmd(mm, dst_addr);
                if (unlikely(!dst_pmd)) {
                        err = -ENOMEM;
                        break;
                }

                dst_pmdval = pmdp_get_lockless(dst_pmd);
                /*
                 * If the dst_pmd is mapped as THP don't override it and just
                 * be strict. If dst_pmd changes into TPH after this check, the
                 * move_pages_huge_pmd() will detect the change and retry
                 * while move_pages_pte() will detect the change and fail.
                 */
                if (unlikely(pmd_trans_huge(dst_pmdval))) {
                        err = -EEXIST;
                        break;
                }

                ptl = pmd_trans_huge_lock(src_pmd, src_vma);
                if (ptl) {
                        /* Check if we can move the pmd without splitting it. */
                        if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) ||
                            !pmd_none(dst_pmdval)) {
                                /* Can be a migration entry */
                                if (pmd_present(*src_pmd)) {
                                        struct folio *folio = pmd_folio(*src_pmd);

                                        if (!is_huge_zero_folio(folio) &&
                                            !PageAnonExclusive(&folio->page)) {
                                                spin_unlock(ptl);
                                                err = -EBUSY;
                                                break;
                                        }
                                }

                                spin_unlock(ptl);
                                split_huge_pmd(src_vma, src_pmd, src_addr);
                                /* The folio will be split by move_pages_pte() */
                                continue;
                        }

                        err = move_pages_huge_pmd(mm, dst_pmd, src_pmd,
                                                  dst_pmdval, dst_vma, src_vma,
                                                  dst_addr, src_addr);
                        step_size = HPAGE_PMD_SIZE;
                } else {
                        long ret;

                        if (pmd_none(*src_pmd)) {
                                if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) {
                                        err = -ENOENT;
                                        break;
                                }
                                if (unlikely(__pte_alloc(mm, src_pmd))) {
                                        err = -ENOMEM;
                                        break;
                                }
                        }

                        if (unlikely(pte_alloc(mm, dst_pmd))) {
                                err = -ENOMEM;
                                break;
                        }

                        ret = move_pages_ptes(mm, dst_pmd, src_pmd,
                                              dst_vma, src_vma, dst_addr,
                                              src_addr, src_end - src_addr, mode);
                        if (ret < 0)
                                err = ret;
                        else
                                step_size = ret;
                }

                cond_resched();

                if (fatal_signal_pending(current)) {
                        /* Do not override an error */
                        if (!err || err == -EAGAIN)
                                err = -EINTR;
                        break;
                }

                if (err) {
                        if (err == -EAGAIN)
                                continue;
                        break;
                }

                /* Proceed to the next page */
                dst_addr += step_size;
                src_addr += step_size;
                moved += step_size;
        }

out_unlock:
        up_read(&ctx->map_changing_lock);
        uffd_move_unlock(dst_vma, src_vma);
out:
        VM_WARN_ON_ONCE(moved < 0);
        VM_WARN_ON_ONCE(err > 0);
        VM_WARN_ON_ONCE(!moved && !err);
        return moved ? moved : err;
}

static bool vma_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags,
                       bool wp_async)
{
        const struct vm_uffd_ops *ops = vma_uffd_ops(vma);

        if (vma->vm_flags & (VM_DROPPABLE | VM_SHADOW_STACK))
                return false;

        if (!is_vm_hugetlb_page(vma) && (vma->vm_flags & VM_SPECIAL))
                return false;

        vm_flags &= __VM_UFFD_FLAGS;

        /*
         * If WP is the only mode enabled and context is wp async, allow any
         * memory type.
         */
        if (wp_async && (vm_flags == VM_UFFD_WP))
                return true;

        /* For any other mode reject VMAs that don't implement vm_uffd_ops */
        if (!ops)
                return false;

        /*
         * If user requested uffd-wp but not enabled pte markers for
         * uffd-wp, then only anonymous memory is supported
         */
        if (!uffd_supports_wp_marker() && (vm_flags & VM_UFFD_WP) &&
            !vma_is_anonymous(vma))
                return false;

        return ops->can_userfault(vma, vm_flags);
}

static void userfaultfd_set_vm_flags(struct vm_area_struct *vma,
                                     vm_flags_t vm_flags)
{
        const bool uffd_wp_changed = (vma->vm_flags ^ vm_flags) & VM_UFFD_WP;

        vm_flags_reset(vma, vm_flags);
        /*
         * For shared mappings, we want to enable writenotify while
         * userfaultfd-wp is enabled (see vma_wants_writenotify()). We'll simply
         * recalculate vma->vm_page_prot whenever userfaultfd-wp changes.
         */
        if ((vma->vm_flags & VM_SHARED) && uffd_wp_changed)
                vma_set_page_prot(vma);
}

static void userfaultfd_set_ctx(struct vm_area_struct *vma,
                                struct userfaultfd_ctx *ctx,
                                vm_flags_t vm_flags)
{
        vma_start_write(vma);
        vma->vm_userfaultfd_ctx = (struct vm_userfaultfd_ctx){ctx};
        userfaultfd_set_vm_flags(vma,
                                 (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags);
}

static void userfaultfd_reset_ctx(struct vm_area_struct *vma)
{
        userfaultfd_set_ctx(vma, NULL, 0);
}

static struct vm_area_struct *userfaultfd_clear_vma(struct vma_iterator *vmi,
                                             struct vm_area_struct *prev,
                                             struct vm_area_struct *vma,
                                             unsigned long start,
                                             unsigned long end)
{
        struct vm_area_struct *ret;
        bool give_up_on_oom = false;
        vma_flags_t new_vma_flags = vma->flags;

        vma_flags_clear_mask(&new_vma_flags, __VMA_UFFD_FLAGS);

        /*
         * If we are modifying only and not splitting, just give up on the merge
         * if OOM prevents us from merging successfully.
         */
        if (start == vma->vm_start && end == vma->vm_end)
                give_up_on_oom = true;

        /* Reset ptes for the whole vma range if wr-protected */
        if (userfaultfd_wp(vma))
                uffd_wp_range(vma, start, end - start, false);

        ret = vma_modify_flags_uffd(vmi, prev, vma, start, end,
                                    &new_vma_flags, NULL_VM_UFFD_CTX,
                                    give_up_on_oom);

        /*
         * In the vma_merge() successful mprotect-like case 8:
         * the next vma was merged into the current one and
         * the current one has not been updated yet.
         */
        if (!IS_ERR(ret))
                userfaultfd_reset_ctx(ret);

        return ret;
}

/* Assumes mmap write lock taken, and mm_struct pinned. */
static int userfaultfd_register_range(struct userfaultfd_ctx *ctx,
                               struct vm_area_struct *vma,
                               vm_flags_t vm_flags,
                               unsigned long start, unsigned long end,
                               bool wp_async)
{
        vma_flags_t vma_flags = legacy_to_vma_flags(vm_flags);
        VMA_ITERATOR(vmi, ctx->mm, start);
        struct vm_area_struct *prev = vma_prev(&vmi);
        unsigned long vma_end;
        vma_flags_t new_vma_flags;

        if (vma->vm_start < start)
                prev = vma;

        for_each_vma_range(vmi, vma, end) {
                cond_resched();

                VM_WARN_ON_ONCE(!vma_can_userfault(vma, vm_flags, wp_async));
                VM_WARN_ON_ONCE(vma->vm_userfaultfd_ctx.ctx &&
                                vma->vm_userfaultfd_ctx.ctx != ctx);
                VM_WARN_ON_ONCE(!vma_test(vma, VMA_MAYWRITE_BIT));

                /*
                 * Nothing to do: this vma is already registered into this
                 * userfaultfd and with the right tracking mode too.
                 */
                if (vma->vm_userfaultfd_ctx.ctx == ctx &&
                    vma_test_all_mask(vma, vma_flags))
                        goto skip;

                if (vma->vm_start > start)
                        start = vma->vm_start;
                vma_end = min(end, vma->vm_end);

                new_vma_flags = vma->flags;
                vma_flags_clear_mask(&new_vma_flags, __VMA_UFFD_FLAGS);
                vma_flags_set_mask(&new_vma_flags, vma_flags);

                vma = vma_modify_flags_uffd(&vmi, prev, vma, start, vma_end,
                                            &new_vma_flags,
                                            (struct vm_userfaultfd_ctx){ctx},
                                            /* give_up_on_oom = */false);
                if (IS_ERR(vma))
                        return PTR_ERR(vma);

                /*
                 * In the vma_merge() successful mprotect-like case 8:
                 * the next vma was merged into the current one and
                 * the current one has not been updated yet.
                 */
                userfaultfd_set_ctx(vma, ctx, vm_flags);

                if (is_vm_hugetlb_page(vma) && uffd_disable_huge_pmd_share(vma))
                        hugetlb_unshare_all_pmds(vma);

skip:
                prev = vma;
                start = vma->vm_end;
        }

        return 0;
}

static void userfaultfd_release_new(struct userfaultfd_ctx *ctx)
{
        struct mm_struct *mm = ctx->mm;
        struct vm_area_struct *vma;
        VMA_ITERATOR(vmi, mm, 0);

        /* the various vma->vm_userfaultfd_ctx still points to it */
        mmap_write_lock(mm);
        for_each_vma(vmi, vma) {
                if (vma->vm_userfaultfd_ctx.ctx == ctx)
                        userfaultfd_reset_ctx(vma);
        }
        mmap_write_unlock(mm);
}

static void userfaultfd_release_all(struct mm_struct *mm,
                             struct userfaultfd_ctx *ctx)
{
        struct vm_area_struct *vma, *prev;
        VMA_ITERATOR(vmi, mm, 0);

        if (!mmget_not_zero(mm))
                return;

        /*
         * Flush page faults out of all CPUs. NOTE: all page faults
         * must be retried without returning VM_FAULT_SIGBUS if
         * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
         * changes while handle_userfault released the mmap_lock. So
         * it's critical that released is set to true (above), before
         * taking the mmap_lock for writing.
         */
        mmap_write_lock(mm);
        prev = NULL;
        for_each_vma(vmi, vma) {
                cond_resched();
                VM_WARN_ON_ONCE(!!vma->vm_userfaultfd_ctx.ctx ^
                                !!(vma->vm_flags & __VM_UFFD_FLAGS));
                if (vma->vm_userfaultfd_ctx.ctx != ctx) {
                        prev = vma;
                        continue;
                }

                vma = userfaultfd_clear_vma(&vmi, prev, vma,
                                            vma->vm_start, vma->vm_end);
                prev = vma;
        }
        mmap_write_unlock(mm);
        mmput(mm);
}

static int sysctl_unprivileged_userfaultfd __read_mostly;

#ifdef CONFIG_SYSCTL
static const struct ctl_table vm_userfaultfd_table[] = {
        {
                .procname       = "unprivileged_userfaultfd",
                .data           = &sysctl_unprivileged_userfaultfd,
                .maxlen         = sizeof(sysctl_unprivileged_userfaultfd),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = SYSCTL_ZERO,
                .extra2         = SYSCTL_ONE,
        },
};
#endif

static struct kmem_cache *userfaultfd_ctx_cachep __ro_after_init;

struct userfaultfd_fork_ctx {
        struct userfaultfd_ctx *orig;
        struct userfaultfd_ctx *new;
        struct list_head list;
};

struct userfaultfd_unmap_ctx {
        struct userfaultfd_ctx *ctx;
        unsigned long start;
        unsigned long end;
        struct list_head list;
};

struct userfaultfd_wait_queue {
        struct uffd_msg msg;
        wait_queue_entry_t wq;
        struct userfaultfd_ctx *ctx;
        bool waken;
};

struct userfaultfd_wake_range {
        unsigned long start;
        unsigned long len;
};

/* internal indication that UFFD_API ioctl was successfully executed */
#define UFFD_FEATURE_INITIALIZED                (1u << 31)

static bool userfaultfd_is_initialized(struct userfaultfd_ctx *ctx)
{
        return ctx->features & UFFD_FEATURE_INITIALIZED;
}

static bool userfaultfd_wp_async_ctx(struct userfaultfd_ctx *ctx)
{
        return ctx && (ctx->features & UFFD_FEATURE_WP_ASYNC);
}

/*
 * Whether WP_UNPOPULATED is enabled on the uffd context.  It is only
 * meaningful when userfaultfd_wp()==true on the vma and when it's
 * anonymous.
 */
bool userfaultfd_wp_unpopulated(struct vm_area_struct *vma)
{
        struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;

        if (!ctx)
                return false;

        return ctx->features & UFFD_FEATURE_WP_UNPOPULATED;
}

static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode,
                                     int wake_flags, void *key)
{
        struct userfaultfd_wake_range *range = key;
        int ret;
        struct userfaultfd_wait_queue *uwq;
        unsigned long start, len;

        uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
        ret = 0;
        /* len == 0 means wake all */
        start = range->start;
        len = range->len;
        if (len && (start > uwq->msg.arg.pagefault.address ||
                    start + len <= uwq->msg.arg.pagefault.address))
                goto out;
        WRITE_ONCE(uwq->waken, true);
        /*
         * The Program-Order guarantees provided by the scheduler
         * ensure uwq->waken is visible before the task is woken.
         */
        ret = wake_up_state(wq->private, mode);
        if (ret) {
                /*
                 * Wake only once, autoremove behavior.
                 *
                 * After the effect of list_del_init is visible to the other
                 * CPUs, the waitqueue may disappear from under us, see the
                 * !list_empty_careful() in handle_userfault().
                 *
                 * try_to_wake_up() has an implicit smp_mb(), and the
                 * wq->private is read before calling the extern function
                 * "wake_up_state" (which in turns calls try_to_wake_up).
                 */
                list_del_init(&wq->entry);
        }
out:
        return ret;
}

/**
 * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd
 * context.
 * @ctx: [in] Pointer to the userfaultfd context.
 */
static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
{
        refcount_inc(&ctx->refcount);
}

/**
 * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd
 * context.
 * @ctx: [in] Pointer to userfaultfd context.
 *
 * The userfaultfd context reference must have been previously acquired either
 * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget().
 */
static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
{
        if (refcount_dec_and_test(&ctx->refcount)) {
                VM_WARN_ON_ONCE(spin_is_locked(&ctx->fault_pending_wqh.lock));
                VM_WARN_ON_ONCE(waitqueue_active(&ctx->fault_pending_wqh));
                VM_WARN_ON_ONCE(spin_is_locked(&ctx->fault_wqh.lock));
                VM_WARN_ON_ONCE(waitqueue_active(&ctx->fault_wqh));
                VM_WARN_ON_ONCE(spin_is_locked(&ctx->event_wqh.lock));
                VM_WARN_ON_ONCE(waitqueue_active(&ctx->event_wqh));
                VM_WARN_ON_ONCE(spin_is_locked(&ctx->fd_wqh.lock));
                VM_WARN_ON_ONCE(waitqueue_active(&ctx->fd_wqh));
                mmdrop(ctx->mm);
                kmem_cache_free(userfaultfd_ctx_cachep, ctx);
        }
}

static inline void msg_init(struct uffd_msg *msg)
{
        BUILD_BUG_ON(sizeof(struct uffd_msg) != 32);
        /*
         * Must use memset to zero out the paddings or kernel data is
         * leaked to userland.
         */
        memset(msg, 0, sizeof(struct uffd_msg));
}

static inline struct uffd_msg userfault_msg(unsigned long address,
                                            unsigned long real_address,
                                            unsigned int flags,
                                            unsigned long reason,
                                            unsigned int features)
{
        struct uffd_msg msg;

        msg_init(&msg);
        msg.event = UFFD_EVENT_PAGEFAULT;

        msg.arg.pagefault.address = (features & UFFD_FEATURE_EXACT_ADDRESS) ?
                                    real_address : address;

        /*
         * These flags indicate why the userfault occurred:
         * - UFFD_PAGEFAULT_FLAG_WP indicates a write protect fault.
         * - UFFD_PAGEFAULT_FLAG_MINOR indicates a minor fault.
         * - Neither of these flags being set indicates a MISSING fault.
         *
         * Separately, UFFD_PAGEFAULT_FLAG_WRITE indicates it was a write
         * fault. Otherwise, it was a read fault.
         */
        if (flags & FAULT_FLAG_WRITE)
                msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
        if (reason & VM_UFFD_WP)
                msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
        if (reason & VM_UFFD_MINOR)
                msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_MINOR;
        if (features & UFFD_FEATURE_THREAD_ID)
                msg.arg.pagefault.feat.ptid = task_pid_vnr(current);
        return msg;
}

#ifdef CONFIG_HUGETLB_PAGE
/*
 * Same functionality as userfaultfd_must_wait below with modifications for
 * hugepmd ranges.
 */
static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
                                              struct vm_fault *vmf,
                                              unsigned long reason)
{
        struct vm_area_struct *vma = vmf->vma;
        pte_t *ptep, pte;

        assert_fault_locked(vmf);

        ptep = hugetlb_walk(vma, vmf->address, vma_mmu_pagesize(vma));
        if (!ptep)
                return true;

        pte = huge_ptep_get(vma->vm_mm, vmf->address, ptep);

        /*
         * Lockless access: we're in a wait_event so it's ok if it
         * changes under us.
         */

        /* Entry is still missing, wait for userspace to resolve the fault. */
        if (huge_pte_none(pte))
                return true;
        /* UFFD PTE markers require userspace to resolve the fault. */
        if (pte_is_uffd_marker(pte))
                return true;
        /*
         * Concurrent migration may have replaced the present PTE with a
         * non-marker swap entry between fault delivery and this lockless
         * re-check. huge_pte_write() on a swap entry decodes random offset
         * bits, so gate it on pte_present(). The migration completion path
         * will re-deliver the fault if it still needs userspace.
         */
        if (!pte_present(pte))
                return false;
        /*
         * If VMA has UFFD WP faults enabled and WP fault, wait for userspace to
         * resolve the fault.
         */
        if (!huge_pte_write(pte) && (reason & VM_UFFD_WP))
                return true;

        return false;
}
#else
static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
                                              struct vm_fault *vmf,
                                              unsigned long reason)
{
        /* Should never get here. */
        VM_WARN_ON_ONCE(1);
        return false;
}
#endif /* CONFIG_HUGETLB_PAGE */

/*
 * Verify the pagetables are still not ok after having registered into
 * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
 * userfault that has already been resolved, if userfaultfd_read_iter and
 * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
 * threads.
 */
static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
                                         struct vm_fault *vmf,
                                         unsigned long reason)
{
        struct mm_struct *mm = ctx->mm;
        unsigned long address = vmf->address;
        pgd_t *pgd;
        p4d_t *p4d;
        pud_t *pud;
        pmd_t *pmd, _pmd;
        pte_t *pte;
        pte_t ptent;
        bool ret;

        assert_fault_locked(vmf);

        pgd = pgd_offset(mm, address);
        if (!pgd_present(*pgd))
                return true;
        p4d = p4d_offset(pgd, address);
        if (!p4d_present(*p4d))
                return true;
        pud = pud_offset(p4d, address);
        if (!pud_present(*pud))
                return true;
        pmd = pmd_offset(pud, address);
again:
        _pmd = pmdp_get_lockless(pmd);
        if (pmd_none(_pmd))
                return true;

        /*
         * A race could arise which would result in a softleaf entry such as
         * migration entry unexpectedly being present in the PMD, so explicitly
         * check for this and bail out if so.
         */
        if (!pmd_present(_pmd))
                return false;

        if (pmd_trans_huge(_pmd))
                return !pmd_write(_pmd) && (reason & VM_UFFD_WP);

        pte = pte_offset_map(pmd, address);
        if (!pte)
                goto again;

        /*
         * Lockless access: we're in a wait_event so it's ok if it
         * changes under us.
         */
        ptent = ptep_get(pte);

        ret = true;
        /* Entry is still missing, wait for userspace to resolve the fault. */
        if (pte_none(ptent))
                goto out;
        /* UFFD PTE markers require userspace to resolve the fault. */
        if (pte_is_uffd_marker(ptent))
                goto out;
        /*
         * Concurrent swap-out / migration may have replaced the present PTE
         * with a non-marker swap entry between fault delivery and this
         * lockless re-check. pte_write() on a swap entry decodes random
         * offset bits, so gate it on pte_present(). The page-in path will
         * re-deliver the fault if it still needs userspace.
         */
        if (!pte_present(ptent)) {
                ret = false;
                goto out;
        }
        /*
         * If VMA has UFFD WP faults enabled and WP fault, wait for userspace to
         * resolve the fault.
         */
        if (!pte_write(ptent) && (reason & VM_UFFD_WP))
                goto out;

        ret = false;
out:
        pte_unmap(pte);
        return ret;
}

static inline unsigned int userfaultfd_get_blocking_state(unsigned int flags)
{
        if (flags & FAULT_FLAG_INTERRUPTIBLE)
                return TASK_INTERRUPTIBLE;

        if (flags & FAULT_FLAG_KILLABLE)
                return TASK_KILLABLE;

        return TASK_UNINTERRUPTIBLE;
}

/*
 * The locking rules involved in returning VM_FAULT_RETRY depending on
 * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
 * FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
 * recommendation in __lock_page_or_retry is not an understatement.
 *
 * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_lock must be released
 * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
 * not set.
 *
 * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
 * set, VM_FAULT_RETRY can still be returned if and only if there are
 * fatal_signal_pending()s, and the mmap_lock must be released before
 * returning it.
 */
vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
{
        struct vm_area_struct *vma = vmf->vma;
        struct mm_struct *mm = vma->vm_mm;
        struct userfaultfd_ctx *ctx;
        struct userfaultfd_wait_queue uwq;
        vm_fault_t ret = VM_FAULT_SIGBUS;
        bool must_wait;
        unsigned int blocking_state;

        /*
         * We don't do userfault handling for the final child pid update
         * and when coredumping (faults triggered by get_dump_page()).
         */
        if (current->flags & (PF_EXITING|PF_DUMPCORE))
                goto out;

        assert_fault_locked(vmf);

        ctx = vma->vm_userfaultfd_ctx.ctx;
        if (!ctx)
                goto out;

        VM_WARN_ON_ONCE(ctx->mm != mm);

        /* Any unrecognized flag is a bug. */
        VM_WARN_ON_ONCE(reason & ~__VM_UFFD_FLAGS);
        /* 0 or > 1 flags set is a bug; we expect exactly 1. */
        VM_WARN_ON_ONCE(!reason || (reason & (reason - 1)));

        if (ctx->features & UFFD_FEATURE_SIGBUS)
                goto out;
        if (!(vmf->flags & FAULT_FLAG_USER) && (ctx->flags & UFFD_USER_MODE_ONLY))
                goto out;

        /*
         * Check that we can return VM_FAULT_RETRY.
         *
         * NOTE: it should become possible to return VM_FAULT_RETRY
         * even if FAULT_FLAG_TRIED is set without leading to gup()
         * -EBUSY failures, if the userfaultfd is to be extended for
         * VM_UFFD_WP tracking and we intend to arm the userfault
         * without first stopping userland access to the memory. For
         * VM_UFFD_MISSING userfaults this is enough for now.
         */
        if (unlikely(!(vmf->flags & FAULT_FLAG_ALLOW_RETRY))) {
                /*
                 * Validate the invariant that nowait must allow retry
                 * to be sure not to return SIGBUS erroneously on
                 * nowait invocations.
                 */
                VM_WARN_ON_ONCE(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);
#ifdef CONFIG_DEBUG_VM
                if (printk_ratelimit()) {
                        pr_warn("FAULT_FLAG_ALLOW_RETRY missing %x\n",
                                vmf->flags);
                        dump_stack();
                }
#endif
                goto out;
        }

        /*
         * Handle nowait, not much to do other than tell it to retry
         * and wait.
         */
        ret = VM_FAULT_RETRY;
        if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
                goto out;

        if (unlikely(READ_ONCE(ctx->released))) {
                /*
                 * If a concurrent release is detected, do not return
                 * VM_FAULT_SIGBUS or VM_FAULT_NOPAGE, but instead always
                 * return VM_FAULT_RETRY with lock released proactively.
                 *
                 * If we were to return VM_FAULT_SIGBUS here, the non
                 * cooperative manager would be instead forced to
                 * always call UFFDIO_UNREGISTER before it can safely
                 * close the uffd, to avoid involuntary SIGBUS triggered.
                 *
                 * If we were to return VM_FAULT_NOPAGE, it would work for
                 * the fault path, in which the lock will be released
                 * later.  However for GUP, faultin_page() does nothing
                 * special on NOPAGE, so GUP would spin retrying without
                 * releasing the mmap read lock, causing possible livelock.
                 *
                 * Here only VM_FAULT_RETRY would make sure the mmap lock
                 * be released immediately, so that the thread concurrently
                 * releasing the userfault would always make progress.
                 */
                release_fault_lock(vmf);
                goto out;
        }

        /* take the reference before dropping the mmap_lock */
        userfaultfd_ctx_get(ctx);

        init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
        uwq.wq.private = current;
        uwq.msg = userfault_msg(vmf->address, vmf->real_address, vmf->flags,
                                reason, ctx->features);
        uwq.ctx = ctx;
        uwq.waken = false;

        blocking_state = userfaultfd_get_blocking_state(vmf->flags);

        /*
         * Take the vma lock now, in order to safely call
         * userfaultfd_huge_must_wait() later. Since acquiring the
         * (sleepable) vma lock can modify the current task state, that
         * must be before explicitly calling set_current_state().
         */
        if (is_vm_hugetlb_page(vma))
                hugetlb_vma_lock_read(vma);

        spin_lock_irq(&ctx->fault_pending_wqh.lock);
        /*
         * After the __add_wait_queue the uwq is visible to userland
         * through poll/read().
         */
        __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq);
        /*
         * The smp_mb() after __set_current_state prevents the reads
         * following the spin_unlock to happen before the list_add in
         * __add_wait_queue.
         */
        set_current_state(blocking_state);
        spin_unlock_irq(&ctx->fault_pending_wqh.lock);

        if (is_vm_hugetlb_page(vma)) {
                must_wait = userfaultfd_huge_must_wait(ctx, vmf, reason);
                hugetlb_vma_unlock_read(vma);
        } else {
                must_wait = userfaultfd_must_wait(ctx, vmf, reason);
        }

        release_fault_lock(vmf);

        if (likely(must_wait && !READ_ONCE(ctx->released))) {
                wake_up_poll(&ctx->fd_wqh, EPOLLIN);
                schedule();
        }

        __set_current_state(TASK_RUNNING);

        /*
         * Here we race with the list_del; list_add in
         * userfaultfd_ctx_read(), however because we don't ever run
         * list_del_init() to refile across the two lists, the prev
         * and next pointers will never point to self. list_add also
         * would never let any of the two pointers to point to
         * self. So list_empty_careful won't risk to see both pointers
         * pointing to self at any time during the list refile. The
         * only case where list_del_init() is called is the full
         * removal in the wake function and there we don't re-list_add
         * and it's fine not to block on the spinlock. The uwq on this
         * kernel stack can be released after the list_del_init.
         */
        if (!list_empty_careful(&uwq.wq.entry)) {
                spin_lock_irq(&ctx->fault_pending_wqh.lock);
                /*
                 * No need of list_del_init(), the uwq on the stack
                 * will be freed shortly anyway.
                 */
                list_del(&uwq.wq.entry);
                spin_unlock_irq(&ctx->fault_pending_wqh.lock);
        }

        /*
         * ctx may go away after this if the userfault pseudo fd is
         * already released.
         */
        userfaultfd_ctx_put(ctx);

out:
        return ret;
}

static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
                                              struct userfaultfd_wait_queue *ewq)
{
        struct userfaultfd_ctx *release_new_ctx;

        if (WARN_ON_ONCE(current->flags & PF_EXITING))
                goto out;

        ewq->ctx = ctx;
        init_waitqueue_entry(&ewq->wq, current);
        release_new_ctx = NULL;

        spin_lock_irq(&ctx->event_wqh.lock);
        /*
         * After the __add_wait_queue the uwq is visible to userland
         * through poll/read().
         */
        __add_wait_queue(&ctx->event_wqh, &ewq->wq);
        for (;;) {
                set_current_state(TASK_KILLABLE);
                if (ewq->msg.event == 0)
                        break;
                if (READ_ONCE(ctx->released) ||
                    fatal_signal_pending(current)) {
                        /*
                         * &ewq->wq may be queued in fork_event, but
                         * __remove_wait_queue ignores the head
                         * parameter. It would be a problem if it
                         * didn't.
                         */
                        __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
                        if (ewq->msg.event == UFFD_EVENT_FORK) {
                                struct userfaultfd_ctx *new;

                                new = (struct userfaultfd_ctx *)
                                        (unsigned long)
                                        ewq->msg.arg.reserved.reserved1;
                                release_new_ctx = new;
                        }
                        break;
                }

                spin_unlock_irq(&ctx->event_wqh.lock);

                wake_up_poll(&ctx->fd_wqh, EPOLLIN);
                schedule();

                spin_lock_irq(&ctx->event_wqh.lock);
        }
        __set_current_state(TASK_RUNNING);
        spin_unlock_irq(&ctx->event_wqh.lock);

        if (release_new_ctx) {
                userfaultfd_release_new(release_new_ctx);
                userfaultfd_ctx_put(release_new_ctx);
        }

        /*
         * ctx may go away after this if the userfault pseudo fd is
         * already released.
         */
out:
        atomic_dec(&ctx->mmap_changing);
        VM_WARN_ON_ONCE(atomic_read(&ctx->mmap_changing) < 0);
        userfaultfd_ctx_put(ctx);
}

static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx,
                                       struct userfaultfd_wait_queue *ewq)
{
        ewq->msg.event = 0;
        wake_up_locked(&ctx->event_wqh);
        __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
}

int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
{
        struct userfaultfd_ctx *ctx = NULL, *octx;
        struct userfaultfd_fork_ctx *fctx;

        octx = vma->vm_userfaultfd_ctx.ctx;
        if (!octx)
                return 0;

        if (!(octx->features & UFFD_FEATURE_EVENT_FORK)) {
                userfaultfd_reset_ctx(vma);
                return 0;
        }

        list_for_each_entry(fctx, fcs, list)
                if (fctx->orig == octx) {
                        ctx = fctx->new;
                        break;
                }

        if (!ctx) {
                fctx = kmalloc_obj(*fctx);
                if (!fctx)
                        return -ENOMEM;

                ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
                if (!ctx) {
                        kfree(fctx);
                        return -ENOMEM;
                }

                refcount_set(&ctx->refcount, 1);
                ctx->flags = octx->flags;
                ctx->features = octx->features;
                ctx->released = false;
                init_rwsem(&ctx->map_changing_lock);
                atomic_set(&ctx->mmap_changing, 0);
                ctx->mm = vma->vm_mm;
                mmgrab(ctx->mm);

                userfaultfd_ctx_get(octx);
                down_write(&octx->map_changing_lock);
                atomic_inc(&octx->mmap_changing);
                up_write(&octx->map_changing_lock);
                fctx->orig = octx;
                fctx->new = ctx;
                list_add_tail(&fctx->list, fcs);
        }

        vma->vm_userfaultfd_ctx.ctx = ctx;
        return 0;
}

static void dup_fctx(struct userfaultfd_fork_ctx *fctx)
{
        struct userfaultfd_ctx *ctx = fctx->orig;
        struct userfaultfd_wait_queue ewq;

        msg_init(&ewq.msg);

        ewq.msg.event = UFFD_EVENT_FORK;
        ewq.msg.arg.reserved.reserved1 = (unsigned long)fctx->new;

        userfaultfd_event_wait_completion(ctx, &ewq);
}

void dup_userfaultfd_complete(struct list_head *fcs)
{
        struct userfaultfd_fork_ctx *fctx, *n;

        list_for_each_entry_safe(fctx, n, fcs, list) {
                dup_fctx(fctx);
                list_del(&fctx->list);
                kfree(fctx);
        }
}

void dup_userfaultfd_fail(struct list_head *fcs)
{
        struct userfaultfd_fork_ctx *fctx, *n;

        /*
         * An error has occurred on fork, we will tear memory down, but have
         * allocated memory for fctx's and raised reference counts for both the
         * original and child contexts (and on the mm for each as a result).
         *
         * These would ordinarily be taken care of by a user handling the event,
         * but we are no longer doing so, so manually clean up here.
         *
         * mm tear down will take care of cleaning up VMA contexts.
         */
        list_for_each_entry_safe(fctx, n, fcs, list) {
                struct userfaultfd_ctx *octx = fctx->orig;
                struct userfaultfd_ctx *ctx = fctx->new;

                atomic_dec(&octx->mmap_changing);
                VM_WARN_ON_ONCE(atomic_read(&octx->mmap_changing) < 0);
                userfaultfd_ctx_put(octx);
                userfaultfd_ctx_put(ctx);

                list_del(&fctx->list);
                kfree(fctx);
        }
}

void mremap_userfaultfd_prep(struct vm_area_struct *vma,
                             struct vm_userfaultfd_ctx *vm_ctx)
{
        struct userfaultfd_ctx *ctx;

        ctx = vma->vm_userfaultfd_ctx.ctx;

        if (!ctx)
                return;

        if (ctx->features & UFFD_FEATURE_EVENT_REMAP) {
                vm_ctx->ctx = ctx;
                userfaultfd_ctx_get(ctx);
                down_write(&ctx->map_changing_lock);
                atomic_inc(&ctx->mmap_changing);
                up_write(&ctx->map_changing_lock);
        } else {
                /* Drop uffd context if remap feature not enabled */
                userfaultfd_reset_ctx(vma);
        }
}

void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx,
                                 unsigned long from, unsigned long to,
                                 unsigned long len)
{
        struct userfaultfd_ctx *ctx = vm_ctx->ctx;
        struct userfaultfd_wait_queue ewq;

        if (!ctx)
                return;

        msg_init(&ewq.msg);

        ewq.msg.event = UFFD_EVENT_REMAP;
        ewq.msg.arg.remap.from = from;
        ewq.msg.arg.remap.to = to;
        ewq.msg.arg.remap.len = len;

        userfaultfd_event_wait_completion(ctx, &ewq);
}

void mremap_userfaultfd_fail(struct vm_userfaultfd_ctx *vm_ctx)
{
        struct userfaultfd_ctx *ctx = vm_ctx->ctx;

        if (!ctx)
                return;

        atomic_dec(&ctx->mmap_changing);
        VM_WARN_ON_ONCE(atomic_read(&ctx->mmap_changing) < 0);
        userfaultfd_ctx_put(ctx);
}

bool userfaultfd_remove(struct vm_area_struct *vma,
                        unsigned long start, unsigned long end)
{
        struct mm_struct *mm = vma->vm_mm;
        struct userfaultfd_ctx *ctx;
        struct userfaultfd_wait_queue ewq;

        ctx = vma->vm_userfaultfd_ctx.ctx;
        if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_REMOVE))
                return true;

        userfaultfd_ctx_get(ctx);
        down_write(&ctx->map_changing_lock);
        atomic_inc(&ctx->mmap_changing);
        up_write(&ctx->map_changing_lock);
        mmap_read_unlock(mm);

        msg_init(&ewq.msg);

        ewq.msg.event = UFFD_EVENT_REMOVE;
        ewq.msg.arg.remove.start = start;
        ewq.msg.arg.remove.end = end;

        userfaultfd_event_wait_completion(ctx, &ewq);

        return false;
}

static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps,
                          unsigned long start, unsigned long end)
{
        struct userfaultfd_unmap_ctx *unmap_ctx;

        list_for_each_entry(unmap_ctx, unmaps, list)
                if (unmap_ctx->ctx == ctx && unmap_ctx->start == start &&
                    unmap_ctx->end == end)
                        return true;

        return false;
}

int userfaultfd_unmap_prep(struct vm_area_struct *vma, unsigned long start,
                           unsigned long end, struct list_head *unmaps)
{
        struct userfaultfd_unmap_ctx *unmap_ctx;
        struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;

        if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_UNMAP) ||
            has_unmap_ctx(ctx, unmaps, start, end))
                return 0;

        unmap_ctx = kzalloc_obj(*unmap_ctx);
        if (!unmap_ctx)
                return -ENOMEM;

        userfaultfd_ctx_get(ctx);
        down_write(&ctx->map_changing_lock);
        atomic_inc(&ctx->mmap_changing);
        up_write(&ctx->map_changing_lock);
        unmap_ctx->ctx = ctx;
        unmap_ctx->start = start;
        unmap_ctx->end = end;
        list_add_tail(&unmap_ctx->list, unmaps);

        return 0;
}

void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf)
{
        struct userfaultfd_unmap_ctx *ctx, *n;
        struct userfaultfd_wait_queue ewq;

        list_for_each_entry_safe(ctx, n, uf, list) {
                msg_init(&ewq.msg);

                ewq.msg.event = UFFD_EVENT_UNMAP;
                ewq.msg.arg.remove.start = ctx->start;
                ewq.msg.arg.remove.end = ctx->end;

                userfaultfd_event_wait_completion(ctx->ctx, &ewq);

                list_del(&ctx->list);
                kfree(ctx);
        }
}

static int userfaultfd_release(struct inode *inode, struct file *file)
{
        struct userfaultfd_ctx *ctx = file->private_data;
        struct mm_struct *mm = ctx->mm;
        /* len == 0 means wake all */
        struct userfaultfd_wake_range range = { .len = 0, };

        WRITE_ONCE(ctx->released, true);

        userfaultfd_release_all(mm, ctx);

        /*
         * After no new page faults can wait on this fault_*wqh, flush
         * the last page faults that may have been already waiting on
         * the fault_*wqh.
         */
        spin_lock_irq(&ctx->fault_pending_wqh.lock);
        __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
        __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, &range);
        spin_unlock_irq(&ctx->fault_pending_wqh.lock);

        /* Flush pending events that may still wait on event_wqh */
        wake_up_all(&ctx->event_wqh);

        wake_up_poll(&ctx->fd_wqh, EPOLLHUP);
        userfaultfd_ctx_put(ctx);
        return 0;
}

/* fault_pending_wqh.lock must be hold by the caller */
static inline struct userfaultfd_wait_queue *find_userfault_in(
                wait_queue_head_t *wqh)
{
        wait_queue_entry_t *wq;
        struct userfaultfd_wait_queue *uwq;

        lockdep_assert_held(&wqh->lock);

        uwq = NULL;
        if (!waitqueue_active(wqh))
                goto out;
        /* walk in reverse to provide FIFO behavior to read userfaults */
        wq = list_last_entry(&wqh->head, typeof(*wq), entry);
        uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
out:
        return uwq;
}

static inline struct userfaultfd_wait_queue *find_userfault(
                struct userfaultfd_ctx *ctx)
{
        return find_userfault_in(&ctx->fault_pending_wqh);
}

static inline struct userfaultfd_wait_queue *find_userfault_evt(
                struct userfaultfd_ctx *ctx)
{
        return find_userfault_in(&ctx->event_wqh);
}

static __poll_t userfaultfd_poll(struct file *file, poll_table *wait)
{
        struct userfaultfd_ctx *ctx = file->private_data;
        __poll_t ret;

        poll_wait(file, &ctx->fd_wqh, wait);

        if (!userfaultfd_is_initialized(ctx))
                return EPOLLERR;

        /*
         * poll() never guarantees that read won't block.
         * userfaults can be waken before they're read().
         */
        if (unlikely(!(file->f_flags & O_NONBLOCK)))
                return EPOLLERR;
        /*
         * lockless access to see if there are pending faults
         * __pollwait last action is the add_wait_queue but
         * the spin_unlock would allow the waitqueue_active to
         * pass above the actual list_add inside
         * add_wait_queue critical section. So use a full
         * memory barrier to serialize the list_add write of
         * add_wait_queue() with the waitqueue_active read
         * below.
         */
        ret = 0;
        smp_mb();
        if (waitqueue_active(&ctx->fault_pending_wqh))
                ret = EPOLLIN;
        else if (waitqueue_active(&ctx->event_wqh))
                ret = EPOLLIN;

        return ret;
}

static const struct file_operations userfaultfd_fops;

static int resolve_userfault_fork(struct userfaultfd_ctx *new,
                                  struct inode *inode,
                                  struct uffd_msg *msg)
{
        int fd;

        fd = anon_inode_create_getfd("[userfaultfd]", &userfaultfd_fops, new,
                        O_RDONLY | (new->flags & UFFD_SHARED_FCNTL_FLAGS), inode);
        if (fd < 0)
                return fd;

        msg->arg.reserved.reserved1 = 0;
        msg->arg.fork.ufd = fd;
        return 0;
}

static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
                                    struct uffd_msg *msg, struct inode *inode)
{
        ssize_t ret;
        DECLARE_WAITQUEUE(wait, current);
        struct userfaultfd_wait_queue *uwq;
        /*
         * Handling fork event requires sleeping operations, so
         * we drop the event_wqh lock, then do these ops, then
         * lock it back and wake up the waiter. While the lock is
         * dropped the ewq may go away so we keep track of it
         * carefully.
         */
        LIST_HEAD(fork_event);
        struct userfaultfd_ctx *fork_nctx = NULL;

        /* always take the fd_wqh lock before the fault_pending_wqh lock */
        spin_lock_irq(&ctx->fd_wqh.lock);
        __add_wait_queue(&ctx->fd_wqh, &wait);
        for (;;) {
                set_current_state(TASK_INTERRUPTIBLE);
                spin_lock(&ctx->fault_pending_wqh.lock);
                uwq = find_userfault(ctx);
                if (uwq) {
                        /*
                         * Use a seqcount to repeat the lockless check
                         * in wake_userfault() to avoid missing
                         * wakeups because during the refile both
                         * waitqueue could become empty if this is the
                         * only userfault.
                         */
                        write_seqcount_begin(&ctx->refile_seq);

                        /*
                         * The fault_pending_wqh.lock prevents the uwq
                         * to disappear from under us.
                         *
                         * Refile this userfault from
                         * fault_pending_wqh to fault_wqh, it's not
                         * pending anymore after we read it.
                         *
                         * Use list_del() by hand (as
                         * userfaultfd_wake_function also uses
                         * list_del_init() by hand) to be sure nobody
                         * changes __remove_wait_queue() to use
                         * list_del_init() in turn breaking the
                         * !list_empty_careful() check in
                         * handle_userfault(). The uwq->wq.head list
                         * must never be empty at any time during the
                         * refile, or the waitqueue could disappear
                         * from under us. The "wait_queue_head_t"
                         * parameter of __remove_wait_queue() is unused
                         * anyway.
                         */
                        list_del(&uwq->wq.entry);
                        add_wait_queue(&ctx->fault_wqh, &uwq->wq);

                        write_seqcount_end(&ctx->refile_seq);

                        /* careful to always initialize msg if ret == 0 */
                        *msg = uwq->msg;
                        spin_unlock(&ctx->fault_pending_wqh.lock);
                        ret = 0;
                        break;
                }
                spin_unlock(&ctx->fault_pending_wqh.lock);

                spin_lock(&ctx->event_wqh.lock);
                uwq = find_userfault_evt(ctx);
                if (uwq) {
                        *msg = uwq->msg;

                        if (uwq->msg.event == UFFD_EVENT_FORK) {
                                fork_nctx = (struct userfaultfd_ctx *)
                                        (unsigned long)
                                        uwq->msg.arg.reserved.reserved1;
                                list_move(&uwq->wq.entry, &fork_event);
                                /*
                                 * fork_nctx can be freed as soon as
                                 * we drop the lock, unless we take a
                                 * reference on it.
                                 */
                                userfaultfd_ctx_get(fork_nctx);
                                spin_unlock(&ctx->event_wqh.lock);
                                ret = 0;
                                break;
                        }

                        userfaultfd_event_complete(ctx, uwq);
                        spin_unlock(&ctx->event_wqh.lock);
                        ret = 0;
                        break;
                }
                spin_unlock(&ctx->event_wqh.lock);

                if (signal_pending(current)) {
                        ret = -ERESTARTSYS;
                        break;
                }
                if (no_wait) {
                        ret = -EAGAIN;
                        break;
                }
                spin_unlock_irq(&ctx->fd_wqh.lock);
                schedule();
                spin_lock_irq(&ctx->fd_wqh.lock);
        }
        __remove_wait_queue(&ctx->fd_wqh, &wait);
        __set_current_state(TASK_RUNNING);
        spin_unlock_irq(&ctx->fd_wqh.lock);

        if (!ret && msg->event == UFFD_EVENT_FORK) {
                ret = resolve_userfault_fork(fork_nctx, inode, msg);
                spin_lock_irq(&ctx->event_wqh.lock);
                if (!list_empty(&fork_event)) {
                        /*
                         * The fork thread didn't abort, so we can
                         * drop the temporary refcount.
                         */
                        userfaultfd_ctx_put(fork_nctx);

                        uwq = list_first_entry(&fork_event,
                                               typeof(*uwq),
                                               wq.entry);
                        /*
                         * If fork_event list wasn't empty and in turn
                         * the event wasn't already released by fork
                         * (the event is allocated on fork kernel
                         * stack), put the event back to its place in
                         * the event_wq. fork_event head will be freed
                         * as soon as we return so the event cannot
                         * stay queued there no matter the current
                         * "ret" value.
                         */
                        list_del(&uwq->wq.entry);
                        __add_wait_queue(&ctx->event_wqh, &uwq->wq);

                        /*
                         * Leave the event in the waitqueue and report
                         * error to userland if we failed to resolve
                         * the userfault fork.
                         */
                        if (likely(!ret))
                                userfaultfd_event_complete(ctx, uwq);
                } else {
                        /*
                         * Here the fork thread aborted and the
                         * refcount from the fork thread on fork_nctx
                         * has already been released. We still hold
                         * the reference we took before releasing the
                         * lock above. If resolve_userfault_fork
                         * failed we've to drop it because the
                         * fork_nctx has to be freed in such case. If
                         * it succeeded we'll hold it because the new
                         * uffd references it.
                         */
                        if (ret)
                                userfaultfd_ctx_put(fork_nctx);
                }
                spin_unlock_irq(&ctx->event_wqh.lock);
        }

        return ret;
}

static ssize_t userfaultfd_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
        struct file *file = iocb->ki_filp;
        struct userfaultfd_ctx *ctx = file->private_data;
        ssize_t _ret, ret = 0;
        struct uffd_msg msg;
        struct inode *inode = file_inode(file);
        bool no_wait;

        if (!userfaultfd_is_initialized(ctx))
                return -EINVAL;

        no_wait = file->f_flags & O_NONBLOCK || iocb->ki_flags & IOCB_NOWAIT;
        for (;;) {
                if (iov_iter_count(to) < sizeof(msg))
                        return ret ? ret : -EINVAL;
                _ret = userfaultfd_ctx_read(ctx, no_wait, &msg, inode);
                if (_ret < 0)
                        return ret ? ret : _ret;
                _ret = !copy_to_iter_full(&msg, sizeof(msg), to);
                if (_ret)
                        return ret ? ret : -EFAULT;
                ret += sizeof(msg);
                /*
                 * Allow to read more than one fault at time but only
                 * block if waiting for the very first one.
                 */
                no_wait = true;
        }
}

static void __wake_userfault(struct userfaultfd_ctx *ctx,
                             struct userfaultfd_wake_range *range)
{
        spin_lock_irq(&ctx->fault_pending_wqh.lock);
        /* wake all in the range and autoremove */
        if (waitqueue_active(&ctx->fault_pending_wqh))
                __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,
                                     range);
        if (waitqueue_active(&ctx->fault_wqh))
                __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, range);
        spin_unlock_irq(&ctx->fault_pending_wqh.lock);
}

static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
                                           struct userfaultfd_wake_range *range)
{
        unsigned seq;
        bool need_wakeup;

        /*
         * To be sure waitqueue_active() is not reordered by the CPU
         * before the pagetable update, use an explicit SMP memory
         * barrier here. PT lock release or mmap_read_unlock(mm) still
         * have release semantics that can allow the
         * waitqueue_active() to be reordered before the pte update.
         */
        smp_mb();

        /*
         * Use waitqueue_active because it's very frequent to
         * change the address space atomically even if there are no
         * userfaults yet. So we take the spinlock only when we're
         * sure we've userfaults to wake.
         */
        do {
                seq = read_seqcount_begin(&ctx->refile_seq);
                need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) ||
                        waitqueue_active(&ctx->fault_wqh);
                cond_resched();
        } while (read_seqcount_retry(&ctx->refile_seq, seq));
        if (need_wakeup)
                __wake_userfault(ctx, range);
}

static __always_inline int validate_unaligned_range(
        struct mm_struct *mm, __u64 start, __u64 len)
{
        __u64 task_size = mm->task_size;

        if (len & ~PAGE_MASK)
                return -EINVAL;
        if (!len)
                return -EINVAL;
        if (start >= task_size)
                return -EINVAL;
        if (len > task_size - start)
                return -EINVAL;
        if (start + len <= start)
                return -EINVAL;
        return 0;
}

static __always_inline int validate_range(struct mm_struct *mm,
                                          __u64 start, __u64 len)
{
        if (start & ~PAGE_MASK)
                return -EINVAL;

        return validate_unaligned_range(mm, start, len);
}

static int userfaultfd_register(struct userfaultfd_ctx *ctx,
                                unsigned long arg)
{
        struct mm_struct *mm = ctx->mm;
        struct vm_area_struct *vma, *cur;
        int ret;
        struct uffdio_register uffdio_register;
        struct uffdio_register __user *user_uffdio_register;
        vm_flags_t vm_flags;
        bool found;
        bool basic_ioctls;
        unsigned long start, end;
        struct vma_iterator vmi;
        bool wp_async = userfaultfd_wp_async_ctx(ctx);

        user_uffdio_register = (struct uffdio_register __user *) arg;

        ret = -EFAULT;
        if (copy_from_user(&uffdio_register, user_uffdio_register,
                           sizeof(uffdio_register)-sizeof(__u64)))
                goto out;

        ret = -EINVAL;
        if (!uffdio_register.mode)
                goto out;
        if (uffdio_register.mode & ~UFFD_API_REGISTER_MODES)
                goto out;
        vm_flags = 0;
        if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
                vm_flags |= VM_UFFD_MISSING;
        if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
                if (!pgtable_supports_uffd_wp())
                        goto out;

                vm_flags |= VM_UFFD_WP;
        }
        if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR) {
#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
                goto out;
#endif
                vm_flags |= VM_UFFD_MINOR;
        }

        ret = validate_range(mm, uffdio_register.range.start,
                             uffdio_register.range.len);
        if (ret)
                goto out;

        start = uffdio_register.range.start;
        end = start + uffdio_register.range.len;

        ret = -ENOMEM;
        if (!mmget_not_zero(mm))
                goto out;

        ret = -EINVAL;
        mmap_write_lock(mm);
        vma_iter_init(&vmi, mm, start);
        vma = vma_find(&vmi, end);
        if (!vma)
                goto out_unlock;

        /*
         * If the first vma contains huge pages, make sure start address
         * is aligned to huge page size.
         */
        if (is_vm_hugetlb_page(vma)) {
                unsigned long vma_hpagesize = vma_kernel_pagesize(vma);

                if (start & (vma_hpagesize - 1))
                        goto out_unlock;
        }

        /*
         * Search for not compatible vmas.
         */
        found = false;
        basic_ioctls = false;
        cur = vma;
        do {
                cond_resched();

                VM_WARN_ON_ONCE(!!cur->vm_userfaultfd_ctx.ctx ^
                                !!(cur->vm_flags & __VM_UFFD_FLAGS));

                /* check not compatible vmas */
                ret = -EINVAL;
                if (!vma_can_userfault(cur, vm_flags, wp_async))
                        goto out_unlock;

                /*
                 * UFFDIO_COPY will fill file holes even without
                 * PROT_WRITE. This check enforces that if this is a
                 * MAP_SHARED, the process has write permission to the backing
                 * file. If VM_MAYWRITE is set it also enforces that on a
                 * MAP_SHARED vma: there is no F_WRITE_SEAL and no further
                 * F_WRITE_SEAL can be taken until the vma is destroyed.
                 */
                ret = -EPERM;
                if (unlikely(!(cur->vm_flags & VM_MAYWRITE)))
                        goto out_unlock;

                /*
                 * If this vma contains ending address, and huge pages
                 * check alignment.
                 */
                if (is_vm_hugetlb_page(cur) && end <= cur->vm_end &&
                    end > cur->vm_start) {
                        unsigned long vma_hpagesize = vma_kernel_pagesize(cur);

                        ret = -EINVAL;

                        if (end & (vma_hpagesize - 1))
                                goto out_unlock;
                }
                if ((vm_flags & VM_UFFD_WP) && !(cur->vm_flags & VM_MAYWRITE))
                        goto out_unlock;

                /*
                 * Check that this vma isn't already owned by a
                 * different userfaultfd. We can't allow more than one
                 * userfaultfd to own a single vma simultaneously or we
                 * wouldn't know which one to deliver the userfaults to.
                 */
                ret = -EBUSY;
                if (cur->vm_userfaultfd_ctx.ctx &&
                    cur->vm_userfaultfd_ctx.ctx != ctx)
                        goto out_unlock;

                /*
                 * Note vmas containing huge pages
                 */
                if (is_vm_hugetlb_page(cur))
                        basic_ioctls = true;

                found = true;
        } for_each_vma_range(vmi, cur, end);
        VM_WARN_ON_ONCE(!found);

        ret = userfaultfd_register_range(ctx, vma, vm_flags, start, end,
                                         wp_async);

out_unlock:
        mmap_write_unlock(mm);
        mmput(mm);
        if (!ret) {
                __u64 ioctls_out;

                ioctls_out = basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
                        UFFD_API_RANGE_IOCTLS;

                /*
                 * Declare the WP ioctl only if the WP mode is
                 * specified and all checks passed with the range
                 */
                if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_WP))
                        ioctls_out &= ~((__u64)1 << _UFFDIO_WRITEPROTECT);

                /* CONTINUE ioctl is only supported for MINOR ranges. */
                if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR))
                        ioctls_out &= ~((__u64)1 << _UFFDIO_CONTINUE);

                /*
                 * Now that we scanned all vmas we can already tell
                 * userland which ioctls methods are guaranteed to
                 * succeed on this range.
                 */
                if (put_user(ioctls_out, &user_uffdio_register->ioctls))
                        ret = -EFAULT;
        }
out:
        return ret;
}

static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
                                  unsigned long arg)
{
        struct mm_struct *mm = ctx->mm;
        struct vm_area_struct *vma, *prev, *cur;
        int ret;
        struct uffdio_range uffdio_unregister;
        bool found;
        unsigned long start, end, vma_end;
        const void __user *buf = (void __user *)arg;
        struct vma_iterator vmi;
        bool wp_async = userfaultfd_wp_async_ctx(ctx);

        ret = -EFAULT;
        if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
                goto out;

        ret = validate_range(mm, uffdio_unregister.start,
                             uffdio_unregister.len);
        if (ret)
                goto out;

        start = uffdio_unregister.start;
        end = start + uffdio_unregister.len;

        ret = -ENOMEM;
        if (!mmget_not_zero(mm))
                goto out;

        mmap_write_lock(mm);
        ret = -EINVAL;
        vma_iter_init(&vmi, mm, start);
        vma = vma_find(&vmi, end);
        if (!vma)
                goto out_unlock;

        /*
         * If the first vma contains huge pages, make sure start address
         * is aligned to huge page size.
         */
        if (is_vm_hugetlb_page(vma)) {
                unsigned long vma_hpagesize = vma_kernel_pagesize(vma);

                if (start & (vma_hpagesize - 1))
                        goto out_unlock;
        }

        /*
         * Search for not compatible vmas.
         */
        found = false;
        cur = vma;
        do {
                cond_resched();

                VM_WARN_ON_ONCE(!!cur->vm_userfaultfd_ctx.ctx ^
                                !!(cur->vm_flags & __VM_UFFD_FLAGS));

                /*
                 * Prevent unregistering through a different userfaultfd than
                 * the one used for registration.
                 */
                if (cur->vm_userfaultfd_ctx.ctx &&
                    cur->vm_userfaultfd_ctx.ctx != ctx)
                        goto out_unlock;

                /*
                 * Check not compatible vmas, not strictly required
                 * here as not compatible vmas cannot have an
                 * userfaultfd_ctx registered on them, but this
                 * provides for more strict behavior to notice
                 * unregistration errors.
                 */
                if (!vma_can_userfault(cur, cur->vm_flags, wp_async))
                        goto out_unlock;

                found = true;
        } for_each_vma_range(vmi, cur, end);
        VM_WARN_ON_ONCE(!found);

        vma_iter_set(&vmi, start);
        prev = vma_prev(&vmi);
        if (vma->vm_start < start)
                prev = vma;

        ret = 0;
        for_each_vma_range(vmi, vma, end) {
                cond_resched();

                /* VMA not registered with userfaultfd. */
                if (!vma->vm_userfaultfd_ctx.ctx)
                        goto skip;

                VM_WARN_ON_ONCE(vma->vm_userfaultfd_ctx.ctx != ctx);
                VM_WARN_ON_ONCE(!vma_can_userfault(vma, vma->vm_flags, wp_async));
                VM_WARN_ON_ONCE(!(vma->vm_flags & VM_MAYWRITE));

                if (vma->vm_start > start)
                        start = vma->vm_start;
                vma_end = min(end, vma->vm_end);

                if (userfaultfd_missing(vma)) {
                        /*
                         * Wake any concurrent pending userfault while
                         * we unregister, so they will not hang
                         * permanently and it avoids userland to call
                         * UFFDIO_WAKE explicitly.
                         */
                        struct userfaultfd_wake_range range;
                        range.start = start;
                        range.len = vma_end - start;
                        wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range);
                }

                vma = userfaultfd_clear_vma(&vmi, prev, vma,
                                            start, vma_end);
                if (IS_ERR(vma)) {
                        ret = PTR_ERR(vma);
                        break;
                }

skip:
                prev = vma;
                start = vma->vm_end;
        }

out_unlock:
        mmap_write_unlock(mm);
        mmput(mm);
out:
        return ret;
}

/*
 * userfaultfd_wake may be used in combination with the
 * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
 */
static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
                            unsigned long arg)
{
        int ret;
        struct uffdio_range uffdio_wake;
        struct userfaultfd_wake_range range;
        const void __user *buf = (void __user *)arg;

        ret = -EFAULT;
        if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
                goto out;

        ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
        if (ret)
                goto out;

        range.start = uffdio_wake.start;
        range.len = uffdio_wake.len;

        /*
         * len == 0 means wake all and we don't want to wake all here,
         * so check it again to be sure.
         */
        VM_WARN_ON_ONCE(!range.len);

        wake_userfault(ctx, &range);
        ret = 0;

out:
        return ret;
}

static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
                            unsigned long arg)
{
        __s64 ret;
        struct uffdio_copy uffdio_copy;
        struct uffdio_copy __user *user_uffdio_copy;
        struct userfaultfd_wake_range range;
        uffd_flags_t flags = 0;

        user_uffdio_copy = (struct uffdio_copy __user *) arg;

        ret = -EAGAIN;
        if (unlikely(atomic_read(&ctx->mmap_changing))) {
                if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
                        return -EFAULT;
                goto out;
        }

        ret = -EFAULT;
        if (copy_from_user(&uffdio_copy, user_uffdio_copy,
                           /* don't copy "copy" last field */
                           sizeof(uffdio_copy)-sizeof(__s64)))
                goto out;

        ret = validate_unaligned_range(ctx->mm, uffdio_copy.src,
                                       uffdio_copy.len);
        if (ret)
                goto out;
        ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
        if (ret)
                goto out;

        ret = -EINVAL;
        if (uffdio_copy.mode & ~(UFFDIO_COPY_MODE_DONTWAKE|UFFDIO_COPY_MODE_WP))
                goto out;
        if (uffdio_copy.mode & UFFDIO_COPY_MODE_WP)
                flags |= MFILL_ATOMIC_WP;
        if (mmget_not_zero(ctx->mm)) {
                ret = mfill_atomic_copy(ctx, uffdio_copy.dst, uffdio_copy.src,
                                        uffdio_copy.len, flags);
                mmput(ctx->mm);
        } else {
                return -ESRCH;
        }
        if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
                return -EFAULT;
        if (ret < 0)
                goto out;
        VM_WARN_ON_ONCE(!ret);
        /* len == 0 would wake all */
        range.len = ret;
        if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
                range.start = uffdio_copy.dst;
                wake_userfault(ctx, &range);
        }
        ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
out:
        return ret;
}

static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
                                unsigned long arg)
{
        __s64 ret;
        struct uffdio_zeropage uffdio_zeropage;
        struct uffdio_zeropage __user *user_uffdio_zeropage;
        struct userfaultfd_wake_range range;

        user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;

        ret = -EAGAIN;
        if (unlikely(atomic_read(&ctx->mmap_changing))) {
                if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
                        return -EFAULT;
                goto out;
        }

        ret = -EFAULT;
        if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage,
                           /* don't copy "zeropage" last field */
                           sizeof(uffdio_zeropage)-sizeof(__s64)))
                goto out;

        ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
                             uffdio_zeropage.range.len);
        if (ret)
                goto out;
        ret = -EINVAL;
        if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
                goto out;

        if (mmget_not_zero(ctx->mm)) {
                ret = mfill_atomic_zeropage(ctx, uffdio_zeropage.range.start,
                                            uffdio_zeropage.range.len);
                mmput(ctx->mm);
        } else {
                return -ESRCH;
        }
        if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
                return -EFAULT;
        if (ret < 0)
                goto out;
        /* len == 0 would wake all */
        VM_WARN_ON_ONCE(!ret);
        range.len = ret;
        if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
                range.start = uffdio_zeropage.range.start;
                wake_userfault(ctx, &range);
        }
        ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
out:
        return ret;
}

static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx,
                                    unsigned long arg)
{
        int ret;
        struct uffdio_writeprotect uffdio_wp;
        struct uffdio_writeprotect __user *user_uffdio_wp;
        struct userfaultfd_wake_range range;
        bool mode_wp, mode_dontwake;

        if (atomic_read(&ctx->mmap_changing))
                return -EAGAIN;

        user_uffdio_wp = (struct uffdio_writeprotect __user *) arg;

        if (copy_from_user(&uffdio_wp, user_uffdio_wp,
                           sizeof(struct uffdio_writeprotect)))
                return -EFAULT;

        ret = validate_range(ctx->mm, uffdio_wp.range.start,
                             uffdio_wp.range.len);
        if (ret)
                return ret;

        if (uffdio_wp.mode & ~(UFFDIO_WRITEPROTECT_MODE_DONTWAKE |
                               UFFDIO_WRITEPROTECT_MODE_WP))
                return -EINVAL;

        mode_wp = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP;
        mode_dontwake = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE;

        if (mode_wp && mode_dontwake)
                return -EINVAL;

        if (mmget_not_zero(ctx->mm)) {
                ret = mwriteprotect_range(ctx, uffdio_wp.range.start,
                                          uffdio_wp.range.len, mode_wp);
                mmput(ctx->mm);
        } else {
                return -ESRCH;
        }

        if (ret)
                return ret;

        if (!mode_wp && !mode_dontwake) {
                range.start = uffdio_wp.range.start;
                range.len = uffdio_wp.range.len;
                wake_userfault(ctx, &range);
        }
        return ret;
}

static int userfaultfd_continue(struct userfaultfd_ctx *ctx, unsigned long arg)
{
        __s64 ret;
        struct uffdio_continue uffdio_continue;
        struct uffdio_continue __user *user_uffdio_continue;
        struct userfaultfd_wake_range range;
        uffd_flags_t flags = 0;

        user_uffdio_continue = (struct uffdio_continue __user *)arg;

        ret = -EAGAIN;
        if (unlikely(atomic_read(&ctx->mmap_changing))) {
                if (unlikely(put_user(ret, &user_uffdio_continue->mapped)))
                        return -EFAULT;
                goto out;
        }

        ret = -EFAULT;
        if (copy_from_user(&uffdio_continue, user_uffdio_continue,
                           /* don't copy the output fields */
                           sizeof(uffdio_continue) - (sizeof(__s64))))
                goto out;

        ret = validate_range(ctx->mm, uffdio_continue.range.start,
                             uffdio_continue.range.len);
        if (ret)
                goto out;

        ret = -EINVAL;
        if (uffdio_continue.mode & ~(UFFDIO_CONTINUE_MODE_DONTWAKE |
                                     UFFDIO_CONTINUE_MODE_WP))
                goto out;
        if (uffdio_continue.mode & UFFDIO_CONTINUE_MODE_WP)
                flags |= MFILL_ATOMIC_WP;

        if (mmget_not_zero(ctx->mm)) {
                ret = mfill_atomic_continue(ctx, uffdio_continue.range.start,
                                            uffdio_continue.range.len, flags);
                mmput(ctx->mm);
        } else {
                return -ESRCH;
        }

        if (unlikely(put_user(ret, &user_uffdio_continue->mapped)))
                return -EFAULT;
        if (ret < 0)
                goto out;

        /* len == 0 would wake all */
        VM_WARN_ON_ONCE(!ret);
        range.len = ret;
        if (!(uffdio_continue.mode & UFFDIO_CONTINUE_MODE_DONTWAKE)) {
                range.start = uffdio_continue.range.start;
                wake_userfault(ctx, &range);
        }
        ret = range.len == uffdio_continue.range.len ? 0 : -EAGAIN;

out:
        return ret;
}

static inline int userfaultfd_poison(struct userfaultfd_ctx *ctx, unsigned long arg)
{
        __s64 ret;
        struct uffdio_poison uffdio_poison;
        struct uffdio_poison __user *user_uffdio_poison;
        struct userfaultfd_wake_range range;

        user_uffdio_poison = (struct uffdio_poison __user *)arg;

        ret = -EAGAIN;
        if (unlikely(atomic_read(&ctx->mmap_changing))) {
                if (unlikely(put_user(ret, &user_uffdio_poison->updated)))
                        return -EFAULT;
                goto out;
        }

        ret = -EFAULT;
        if (copy_from_user(&uffdio_poison, user_uffdio_poison,
                           /* don't copy the output fields */
                           sizeof(uffdio_poison) - (sizeof(__s64))))
                goto out;

        ret = validate_range(ctx->mm, uffdio_poison.range.start,
                             uffdio_poison.range.len);
        if (ret)
                goto out;

        ret = -EINVAL;
        if (uffdio_poison.mode & ~UFFDIO_POISON_MODE_DONTWAKE)
                goto out;

        if (mmget_not_zero(ctx->mm)) {
                ret = mfill_atomic_poison(ctx, uffdio_poison.range.start,
                                          uffdio_poison.range.len, 0);
                mmput(ctx->mm);
        } else {
                return -ESRCH;
        }

        if (unlikely(put_user(ret, &user_uffdio_poison->updated)))
                return -EFAULT;
        if (ret < 0)
                goto out;

        /* len == 0 would wake all */
        VM_WARN_ON_ONCE(!ret);
        range.len = ret;
        if (!(uffdio_poison.mode & UFFDIO_POISON_MODE_DONTWAKE)) {
                range.start = uffdio_poison.range.start;
                wake_userfault(ctx, &range);
        }
        ret = range.len == uffdio_poison.range.len ? 0 : -EAGAIN;

out:
        return ret;
}

bool userfaultfd_wp_async(struct vm_area_struct *vma)
{
        return userfaultfd_wp_async_ctx(vma->vm_userfaultfd_ctx.ctx);
}

static inline unsigned int uffd_ctx_features(__u64 user_features)
{
        /*
         * For the current set of features the bits just coincide. Set
         * UFFD_FEATURE_INITIALIZED to mark the features as enabled.
         */
        return (unsigned int)user_features | UFFD_FEATURE_INITIALIZED;
}

static int userfaultfd_move(struct userfaultfd_ctx *ctx,
                            unsigned long arg)
{
        __s64 ret;
        struct uffdio_move uffdio_move;
        struct uffdio_move __user *user_uffdio_move;
        struct userfaultfd_wake_range range;
        struct mm_struct *mm = ctx->mm;

        user_uffdio_move = (struct uffdio_move __user *) arg;

        ret = -EAGAIN;
        if (unlikely(atomic_read(&ctx->mmap_changing))) {
                if (unlikely(put_user(ret, &user_uffdio_move->move)))
                        return -EFAULT;
                goto out;
        }

        if (copy_from_user(&uffdio_move, user_uffdio_move,
                           /* don't copy "move" last field */
                           sizeof(uffdio_move)-sizeof(__s64)))
                return -EFAULT;

        /* Do not allow cross-mm moves. */
        if (mm != current->mm)
                return -EINVAL;

        ret = validate_range(mm, uffdio_move.dst, uffdio_move.len);
        if (ret)
                return ret;

        ret = validate_range(mm, uffdio_move.src, uffdio_move.len);
        if (ret)
                return ret;

        if (uffdio_move.mode & ~(UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES|
                                 UFFDIO_MOVE_MODE_DONTWAKE))
                return -EINVAL;

        if (mmget_not_zero(mm)) {
                ret = move_pages(ctx, uffdio_move.dst, uffdio_move.src,
                                 uffdio_move.len, uffdio_move.mode);
                mmput(mm);
        } else {
                return -ESRCH;
        }

        if (unlikely(put_user(ret, &user_uffdio_move->move)))
                return -EFAULT;
        if (ret < 0)
                goto out;

        /* len == 0 would wake all */
        VM_WARN_ON(!ret);
        range.len = ret;
        if (!(uffdio_move.mode & UFFDIO_MOVE_MODE_DONTWAKE)) {
                range.start = uffdio_move.dst;
                wake_userfault(ctx, &range);
        }
        ret = range.len == uffdio_move.len ? 0 : -EAGAIN;

out:
        return ret;
}

/*
 * userland asks for a certain API version and we return which bits
 * and ioctl commands are implemented in this kernel for such API
 * version or -EINVAL if unknown.
 */
static int userfaultfd_api(struct userfaultfd_ctx *ctx,
                           unsigned long arg)
{
        struct uffdio_api uffdio_api;
        void __user *buf = (void __user *)arg;
        unsigned int ctx_features;
        int ret;
        __u64 features;

        ret = -EFAULT;
        if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
                goto out;
        features = uffdio_api.features;
        ret = -EINVAL;
        if (uffdio_api.api != UFFD_API)
                goto err_out;
        ret = -EPERM;
        if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE))
                goto err_out;

        /* WP_ASYNC relies on WP_UNPOPULATED, choose it unconditionally */
        if (features & UFFD_FEATURE_WP_ASYNC)
                features |= UFFD_FEATURE_WP_UNPOPULATED;

        /* report all available features and ioctls to userland */
        uffdio_api.features = UFFD_API_FEATURES;
#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
        uffdio_api.features &=
                ~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM);
#endif
        if (!pgtable_supports_uffd_wp())
                uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;

        if (!uffd_supports_wp_marker()) {
                uffdio_api.features &= ~UFFD_FEATURE_WP_HUGETLBFS_SHMEM;
                uffdio_api.features &= ~UFFD_FEATURE_WP_UNPOPULATED;
                uffdio_api.features &= ~UFFD_FEATURE_WP_ASYNC;
        }

        ret = -EINVAL;
        if (features & ~uffdio_api.features)
                goto err_out;

        uffdio_api.ioctls = UFFD_API_IOCTLS;
        ret = -EFAULT;
        if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
                goto out;

        /* only enable the requested features for this uffd context */
        ctx_features = uffd_ctx_features(features);
        ret = -EINVAL;
        if (cmpxchg(&ctx->features, 0, ctx_features) != 0)
                goto err_out;

        ret = 0;
out:
        return ret;
err_out:
        memset(&uffdio_api, 0, sizeof(uffdio_api));
        if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
                ret = -EFAULT;
        goto out;
}

static long userfaultfd_ioctl(struct file *file, unsigned cmd,
                              unsigned long arg)
{
        int ret = -EINVAL;
        struct userfaultfd_ctx *ctx = file->private_data;

        if (cmd != UFFDIO_API && !userfaultfd_is_initialized(ctx))
                return -EINVAL;

        switch (cmd) {
        case UFFDIO_API:
                ret = userfaultfd_api(ctx, arg);
                break;
        case UFFDIO_REGISTER:
                ret = userfaultfd_register(ctx, arg);
                break;
        case UFFDIO_UNREGISTER:
                ret = userfaultfd_unregister(ctx, arg);
                break;
        case UFFDIO_WAKE:
                ret = userfaultfd_wake(ctx, arg);
                break;
        case UFFDIO_COPY:
                ret = userfaultfd_copy(ctx, arg);
                break;
        case UFFDIO_ZEROPAGE:
                ret = userfaultfd_zeropage(ctx, arg);
                break;
        case UFFDIO_MOVE:
                ret = userfaultfd_move(ctx, arg);
                break;
        case UFFDIO_WRITEPROTECT:
                ret = userfaultfd_writeprotect(ctx, arg);
                break;
        case UFFDIO_CONTINUE:
                ret = userfaultfd_continue(ctx, arg);
                break;
        case UFFDIO_POISON:
                ret = userfaultfd_poison(ctx, arg);
                break;
        }
        return ret;
}

#ifdef CONFIG_PROC_FS
static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
{
        struct userfaultfd_ctx *ctx = f->private_data;
        wait_queue_entry_t *wq;
        unsigned long pending = 0, total = 0;

        spin_lock_irq(&ctx->fault_pending_wqh.lock);
        list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) {
                pending++;
                total++;
        }
        list_for_each_entry(wq, &ctx->fault_wqh.head, entry) {
                total++;
        }
        spin_unlock_irq(&ctx->fault_pending_wqh.lock);

        /*
         * If more protocols will be added, there will be all shown
         * separated by a space. Like this:
         *      protocols: aa:... bb:...
         */
        seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
                   pending, total, UFFD_API, ctx->features,
                   UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
}
#endif

static const struct file_operations userfaultfd_fops = {
#ifdef CONFIG_PROC_FS
        .show_fdinfo    = userfaultfd_show_fdinfo,
#endif
        .release        = userfaultfd_release,
        .poll           = userfaultfd_poll,
        .read_iter      = userfaultfd_read_iter,
        .unlocked_ioctl = userfaultfd_ioctl,
        .compat_ioctl   = compat_ptr_ioctl,
        .llseek         = noop_llseek,
};

static void init_once_userfaultfd_ctx(void *mem)
{
        struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;

        init_waitqueue_head(&ctx->fault_pending_wqh);
        init_waitqueue_head(&ctx->fault_wqh);
        init_waitqueue_head(&ctx->event_wqh);
        init_waitqueue_head(&ctx->fd_wqh);
        seqcount_spinlock_init(&ctx->refile_seq, &ctx->fault_pending_wqh.lock);
}

static int new_userfaultfd(int flags)
{
        struct userfaultfd_ctx *ctx __free(kfree) = NULL;

        VM_WARN_ON_ONCE(!current->mm);

        /* Check the UFFD_* constants for consistency. */
        BUILD_BUG_ON(UFFD_USER_MODE_ONLY & UFFD_SHARED_FCNTL_FLAGS);

        if (flags & ~(UFFD_SHARED_FCNTL_FLAGS | UFFD_USER_MODE_ONLY))
                return -EINVAL;

        ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
        if (!ctx)
                return -ENOMEM;

        refcount_set(&ctx->refcount, 1);
        ctx->flags = flags;
        ctx->features = 0;
        ctx->released = false;
        init_rwsem(&ctx->map_changing_lock);
        atomic_set(&ctx->mmap_changing, 0);
        ctx->mm = current->mm;

        FD_PREPARE(fdf, flags & UFFD_SHARED_FCNTL_FLAGS,
                   anon_inode_create_getfile("[userfaultfd]", &userfaultfd_fops, ctx,
                                             O_RDONLY | (flags & UFFD_SHARED_FCNTL_FLAGS),
                                             NULL));
        if (fdf.err)
                return fdf.err;

        /* prevent the mm struct to be freed */
        mmgrab(ctx->mm);
        fd_prepare_file(fdf)->f_mode |= FMODE_NOWAIT;
        retain_and_null_ptr(ctx);
        return fd_publish(fdf);
}

static inline bool userfaultfd_syscall_allowed(int flags)
{
        /* Userspace-only page faults are always allowed */
        if (flags & UFFD_USER_MODE_ONLY)
                return true;

        /*
         * The user is requesting a userfaultfd which can handle kernel faults.
         * Privileged users are always allowed to do this.
         */
        if (capable(CAP_SYS_PTRACE))
                return true;

        /* Otherwise, access to kernel fault handling is sysctl controlled. */
        return sysctl_unprivileged_userfaultfd;
}

SYSCALL_DEFINE1(userfaultfd, int, flags)
{
        if (!userfaultfd_syscall_allowed(flags))
                return -EPERM;

        return new_userfaultfd(flags);
}

static long userfaultfd_dev_ioctl(struct file *file, unsigned int cmd, unsigned long flags)
{
        if (cmd != USERFAULTFD_IOC_NEW)
                return -EINVAL;

        return new_userfaultfd(flags);
}

static const struct file_operations userfaultfd_dev_fops = {
        .unlocked_ioctl = userfaultfd_dev_ioctl,
        .compat_ioctl = userfaultfd_dev_ioctl,
        .owner = THIS_MODULE,
        .llseek = noop_llseek,
};

static struct miscdevice userfaultfd_misc = {
        .minor = MISC_DYNAMIC_MINOR,
        .name = "userfaultfd",
        .fops = &userfaultfd_dev_fops
};

static int __init userfaultfd_init(void)
{
        int ret;

        ret = misc_register(&userfaultfd_misc);
        if (ret)
                return ret;

        userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
                                                sizeof(struct userfaultfd_ctx),
                                                0,
                                                SLAB_HWCACHE_ALIGN|SLAB_PANIC,
                                                init_once_userfaultfd_ctx);
#ifdef CONFIG_SYSCTL
        register_sysctl_init("vm", vm_userfaultfd_table);
#endif
        return 0;
}
__initcall(userfaultfd_init);