// SPDX-License-Identifier: GPL-2.0
/*
 * mm/rmap.c - physical to virtual reverse mappings
 *
 * Copyright 2001, Rik van Riel <riel@conectiva.com.br>
 *
 * Simple, low overhead reverse mapping scheme.
 * Please try to keep this thing as modular as possible.
 *
 * Provides methods for unmapping each kind of mapped page:
 * the anon methods track anonymous pages, and
 * the file methods track pages belonging to an inode.
 *
 * Original design by Rik van Riel <riel@conectiva.com.br> 2001
 * File methods by Dave McCracken <dmccr@us.ibm.com> 2003, 2004
 * Anonymous methods by Andrea Arcangeli <andrea@suse.de> 2004
 * Contributions by Hugh Dickins 2003, 2004
 */

/*
 * Lock ordering in mm:
 *
 * inode->i_rwsem       (while writing or truncating, not reading or faulting)
 *   mm->mmap_lock
 *     mapping->invalidate_lock (in filemap_fault)
 *       folio_lock
 *         hugetlbfs_i_mmap_rwsem_key (in huge_pmd_share, see hugetlbfs below)
 *           vma_start_write
 *             mapping->i_mmap_rwsem
 *               anon_vma->rwsem
 *                 mm->page_table_lock or pte_lock
 *                   swap_lock (in swap_duplicate, swap_info_get)
 *                     mmlist_lock (in mmput, drain_mmlist and others)
 *                     mapping->private_lock (in block_dirty_folio)
 *                         i_pages lock (widely used)
 *                           lruvec->lru_lock (in folio_lruvec_lock_irq)
 *                     inode->i_lock (in set_page_dirty's __mark_inode_dirty)
 *                     bdi.wb->list_lock (in set_page_dirty's __mark_inode_dirty)
 *                       sb_lock (within inode_lock in fs/fs-writeback.c)
 *                       i_pages lock (widely used, in set_page_dirty,
 *                                 in arch-dependent flush_dcache_mmap_lock,
 *                                 within bdi.wb->list_lock in __sync_single_inode)
 *
 * anon_vma->rwsem,mapping->i_mmap_rwsem   (memory_failure, collect_procs_anon)
 *   ->tasklist_lock
 *     pte map lock
 *
 * hugetlbfs PageHuge() take locks in this order:
 *   hugetlb_fault_mutex (hugetlbfs specific page fault mutex)
 *     vma_lock (hugetlb specific lock for pmd_sharing)
 *       mapping->i_mmap_rwsem (also used for hugetlb pmd sharing)
 *         folio_lock
 */

#include <linux/mm.h>
#include <linux/sched/mm.h>
#include <linux/sched/task.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/leafops.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/ksm.h>
#include <linux/rmap.h>
#include <linux/rcupdate.h>
#include <linux/export.h>
#include <linux/memcontrol.h>
#include <linux/mmu_notifier.h>
#include <linux/migrate.h>
#include <linux/hugetlb.h>
#include <linux/huge_mm.h>
#include <linux/backing-dev.h>
#include <linux/page_idle.h>
#include <linux/memremap.h>
#include <linux/userfaultfd_k.h>
#include <linux/mm_inline.h>
#include <linux/oom.h>

#include <asm/tlb.h>

#define CREATE_TRACE_POINTS
#include <trace/events/migrate.h>

#include "internal.h"
#include "swap.h"

static struct kmem_cache *anon_vma_cachep;
static struct kmem_cache *anon_vma_chain_cachep;

static inline struct anon_vma *anon_vma_alloc(void)
{
        struct anon_vma *anon_vma;

        anon_vma = kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
        if (anon_vma) {
                atomic_set(&anon_vma->refcount, 1);
                anon_vma->num_children = 0;
                anon_vma->num_active_vmas = 0;
                anon_vma->parent = anon_vma;
                /*
                 * Initialise the anon_vma root to point to itself. If called
                 * from fork, the root will be reset to the parents anon_vma.
                 */
                anon_vma->root = anon_vma;
        }

        return anon_vma;
}

static inline void anon_vma_free(struct anon_vma *anon_vma)
{
        VM_BUG_ON(atomic_read(&anon_vma->refcount));

        /*
         * Synchronize against folio_lock_anon_vma_read() such that
         * we can safely hold the lock without the anon_vma getting
         * freed.
         *
         * Relies on the full mb implied by the atomic_dec_and_test() from
         * put_anon_vma() against the acquire barrier implied by
         * down_read_trylock() from folio_lock_anon_vma_read(). This orders:
         *
         * folio_lock_anon_vma_read()   VS      put_anon_vma()
         *   down_read_trylock()                  atomic_dec_and_test()
         *   LOCK                                 MB
         *   atomic_read()                        rwsem_is_locked()
         *
         * LOCK should suffice since the actual taking of the lock must
         * happen _before_ what follows.
         */
        might_sleep();
        if (rwsem_is_locked(&anon_vma->root->rwsem)) {
                anon_vma_lock_write(anon_vma);
                anon_vma_unlock_write(anon_vma);
        }

        kmem_cache_free(anon_vma_cachep, anon_vma);
}

static inline struct anon_vma_chain *anon_vma_chain_alloc(gfp_t gfp)
{
        return kmem_cache_alloc(anon_vma_chain_cachep, gfp);
}

static void anon_vma_chain_free(struct anon_vma_chain *anon_vma_chain)
{
        kmem_cache_free(anon_vma_chain_cachep, anon_vma_chain);
}

static void anon_vma_chain_assign(struct vm_area_struct *vma,
                                  struct anon_vma_chain *avc,
                                  struct anon_vma *anon_vma)
{
        avc->vma = vma;
        avc->anon_vma = anon_vma;
        list_add(&avc->same_vma, &vma->anon_vma_chain);
}

/**
 * __anon_vma_prepare - attach an anon_vma to a memory region
 * @vma: the memory region in question
 *
 * This makes sure the memory mapping described by 'vma' has
 * an 'anon_vma' attached to it, so that we can associate the
 * anonymous pages mapped into it with that anon_vma.
 *
 * The common case will be that we already have one, which
 * is handled inline by anon_vma_prepare(). But if
 * not we either need to find an adjacent mapping that we
 * can re-use the anon_vma from (very common when the only
 * reason for splitting a vma has been mprotect()), or we
 * allocate a new one.
 *
 * Anon-vma allocations are very subtle, because we may have
 * optimistically looked up an anon_vma in folio_lock_anon_vma_read()
 * and that may actually touch the rwsem even in the newly
 * allocated vma (it depends on RCU to make sure that the
 * anon_vma isn't actually destroyed).
 *
 * As a result, we need to do proper anon_vma locking even
 * for the new allocation. At the same time, we do not want
 * to do any locking for the common case of already having
 * an anon_vma.
 */
int __anon_vma_prepare(struct vm_area_struct *vma)
{
        struct mm_struct *mm = vma->vm_mm;
        struct anon_vma *anon_vma, *allocated;
        struct anon_vma_chain *avc;

        mmap_assert_locked(mm);
        might_sleep();

        avc = anon_vma_chain_alloc(GFP_KERNEL);
        if (!avc)
                goto out_enomem;

        anon_vma = find_mergeable_anon_vma(vma);
        allocated = NULL;
        if (!anon_vma) {
                anon_vma = anon_vma_alloc();
                if (unlikely(!anon_vma))
                        goto out_enomem_free_avc;
                anon_vma->num_children++; /* self-parent link for new root */
                allocated = anon_vma;
        }

        anon_vma_lock_write(anon_vma);
        /* page_table_lock to protect against threads */
        spin_lock(&mm->page_table_lock);
        if (likely(!vma->anon_vma)) {
                vma->anon_vma = anon_vma;
                anon_vma_chain_assign(vma, avc, anon_vma);
                anon_vma_interval_tree_insert(avc, &anon_vma->rb_root);
                anon_vma->num_active_vmas++;
                allocated = NULL;
                avc = NULL;
        }
        spin_unlock(&mm->page_table_lock);
        anon_vma_unlock_write(anon_vma);

        if (unlikely(allocated))
                put_anon_vma(allocated);
        if (unlikely(avc))
                anon_vma_chain_free(avc);

        return 0;

 out_enomem_free_avc:
        anon_vma_chain_free(avc);
 out_enomem:
        return -ENOMEM;
}

static void check_anon_vma_clone(struct vm_area_struct *dst,
                                 struct vm_area_struct *src,
                                 enum vma_operation operation)
{
        /* The write lock must be held. */
        mmap_assert_write_locked(src->vm_mm);
        /* If not a fork then must be on same mm. */
        VM_WARN_ON_ONCE(operation != VMA_OP_FORK && dst->vm_mm != src->vm_mm);

        /* If we have anything to do src->anon_vma must be provided. */
        VM_WARN_ON_ONCE(!src->anon_vma && !list_empty(&src->anon_vma_chain));
        VM_WARN_ON_ONCE(!src->anon_vma && dst->anon_vma);
        /* We are establishing a new anon_vma_chain. */
        VM_WARN_ON_ONCE(!list_empty(&dst->anon_vma_chain));
        /*
         * On fork, dst->anon_vma is set NULL (temporarily). Otherwise, anon_vma
         * must be the same across dst and src.
         */
        VM_WARN_ON_ONCE(dst->anon_vma && dst->anon_vma != src->anon_vma);
        /*
         * Essentially equivalent to above - if not a no-op, we should expect
         * dst->anon_vma to be set for everything except a fork.
         */
        VM_WARN_ON_ONCE(operation != VMA_OP_FORK && src->anon_vma &&
                        !dst->anon_vma);
        /* For the anon_vma to be compatible, it can only be singular. */
        VM_WARN_ON_ONCE(operation == VMA_OP_MERGE_UNFAULTED &&
                        !list_is_singular(&src->anon_vma_chain));
#ifdef CONFIG_PER_VMA_LOCK
        /* Only merging an unfaulted VMA leaves the destination attached. */
        VM_WARN_ON_ONCE(operation != VMA_OP_MERGE_UNFAULTED &&
                        vma_is_attached(dst));
#endif
}

static void maybe_reuse_anon_vma(struct vm_area_struct *dst,
                struct anon_vma *anon_vma)
{
        /* If already populated, nothing to do.*/
        if (dst->anon_vma)
                return;

        /*
         * We reuse an anon_vma if any linking VMAs were unmapped and it has
         * only a single child at most.
         */
        if (anon_vma->num_active_vmas > 0)
                return;
        if (anon_vma->num_children > 1)
                return;

        dst->anon_vma = anon_vma;
        anon_vma->num_active_vmas++;
}

static void cleanup_partial_anon_vmas(struct vm_area_struct *vma);

/**
 * anon_vma_clone - Establishes new anon_vma_chain objects in @dst linking to
 * all of the anon_vma objects contained within @src anon_vma_chain's.
 * @dst: The destination VMA with an empty anon_vma_chain.
 * @src: The source VMA we wish to duplicate.
 * @operation: The type of operation which resulted in the clone.
 *
 * This is the heart of the VMA side of the anon_vma implementation - we invoke
 * this function whenever we need to set up a new VMA's anon_vma state.
 *
 * This is invoked for:
 *
 * - VMA Merge, but only when @dst is unfaulted and @src is faulted - meaning we
 *   clone @src into @dst.
 * - VMA split.
 * - VMA (m)remap.
 * - Fork of faulted VMA.
 *
 * In all cases other than fork this is simply a duplication. Fork additionally
 * adds a new active anon_vma.
 *
 * ONLY in the case of fork do we try to 'reuse' existing anon_vma's in an
 * anon_vma hierarchy, reusing anon_vma's which have no VMA associated with them
 * but do have a single child. This is to avoid waste of memory when repeatedly
 * forking.
 *
 * Returns: 0 on success, -ENOMEM on failure.
 */
int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src,
                   enum vma_operation operation)
{
        struct anon_vma_chain *avc, *pavc;
        struct anon_vma *active_anon_vma = src->anon_vma;

        check_anon_vma_clone(dst, src, operation);

        if (!active_anon_vma)
                return 0;

        /*
         * Allocate AVCs. We don't need an anon_vma lock for this as we
         * are not updating the anon_vma rbtree nor are we changing
         * anon_vma statistics.
         *
         * Either src, dst have the same mm for which we hold an exclusive mmap
         * write lock, or we are forking and we hold it on src->vm_mm and dst is
         * not yet accessible to other threads so there's no possibliity of the
         * unlinked AVC's being observed yet.
         */
        list_for_each_entry(pavc, &src->anon_vma_chain, same_vma) {
                avc = anon_vma_chain_alloc(GFP_KERNEL);
                if (!avc)
                        goto enomem_failure;

                anon_vma_chain_assign(dst, avc, pavc->anon_vma);
        }

        /*
         * Now link the anon_vma's back to the newly inserted AVCs.
         * Note that all anon_vma's share the same root.
         */
        anon_vma_lock_write(src->anon_vma);
        list_for_each_entry_reverse(avc, &dst->anon_vma_chain, same_vma) {
                struct anon_vma *anon_vma = avc->anon_vma;

                anon_vma_interval_tree_insert(avc, &anon_vma->rb_root);
                if (operation == VMA_OP_FORK)
                        maybe_reuse_anon_vma(dst, anon_vma);
        }

        if (operation != VMA_OP_FORK)
                dst->anon_vma->num_active_vmas++;

        anon_vma_unlock_write(active_anon_vma);
        return 0;

 enomem_failure:
        cleanup_partial_anon_vmas(dst);
        return -ENOMEM;
}

/*
 * Attach vma to its own anon_vma, as well as to the anon_vmas that
 * the corresponding VMA in the parent process is attached to.
 * Returns 0 on success, non-zero on failure.
 */
int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)
{
        struct anon_vma_chain *avc;
        struct anon_vma *anon_vma;
        int rc;

        /* Don't bother if the parent process has no anon_vma here. */
        if (!pvma->anon_vma)
                return 0;

        /* Drop inherited anon_vma, we'll reuse existing or allocate new. */
        vma->anon_vma = NULL;

        anon_vma = anon_vma_alloc();
        if (!anon_vma)
                return -ENOMEM;
        avc = anon_vma_chain_alloc(GFP_KERNEL);
        if (!avc) {
                put_anon_vma(anon_vma);
                return -ENOMEM;
        }

        /*
         * First, attach the new VMA to the parent VMA's anon_vmas,
         * so rmap can find non-COWed pages in child processes.
         */
        rc = anon_vma_clone(vma, pvma, VMA_OP_FORK);
        /* An error arose or an existing anon_vma was reused, all done then. */
        if (rc || vma->anon_vma) {
                put_anon_vma(anon_vma);
                anon_vma_chain_free(avc);
                return rc;
        }

        /*
         * OK no reuse, so add our own anon_vma.
         *
         * Since it is not linked anywhere we can safely manipulate anon_vma
         * fields without a lock.
         */

        anon_vma->num_active_vmas = 1;
        /*
         * The root anon_vma's rwsem is the lock actually used when we
         * lock any of the anon_vmas in this anon_vma tree.
         */
        anon_vma->root = pvma->anon_vma->root;
        anon_vma->parent = pvma->anon_vma;
        /*
         * With refcounts, an anon_vma can stay around longer than the
         * process it belongs to. The root anon_vma needs to be pinned until
         * this anon_vma is freed, because the lock lives in the root.
         */
        get_anon_vma(anon_vma->root);
        /* Mark this anon_vma as the one where our new (COWed) pages go. */
        vma->anon_vma = anon_vma;
        anon_vma_chain_assign(vma, avc, anon_vma);
        /* Now let rmap see it. */
        anon_vma_lock_write(anon_vma);
        anon_vma_interval_tree_insert(avc, &anon_vma->rb_root);
        anon_vma->parent->num_children++;
        anon_vma_unlock_write(anon_vma);

        return 0;
}

/*
 * In the unfortunate case of anon_vma_clone() failing to allocate memory we
 * have to clean things up.
 *
 * Since we allocate anon_vma_chain's before we insert them into the interval
 * trees, we simply have to free up the AVC's and remove the entries from the
 * VMA's anon_vma_chain.
 */
static void cleanup_partial_anon_vmas(struct vm_area_struct *vma)
{
        struct anon_vma_chain *avc, *next;

        list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
                list_del(&avc->same_vma);
                anon_vma_chain_free(avc);
        }

        /*
         * The anon_vma assigned to this VMA is no longer valid, as we were not
         * able to correctly clone AVC state. Avoid inconsistent anon_vma tree
         * state by resetting.
         */
        vma->anon_vma = NULL;
}

/**
 * unlink_anon_vmas() - remove all links between a VMA and anon_vma's, freeing
 * anon_vma_chain objects.
 * @vma: The VMA whose links to anon_vma objects is to be severed.
 *
 * As part of the process anon_vma_chain's are freed,
 * anon_vma->num_children,num_active_vmas is updated as required and, if the
 * relevant anon_vma references no further VMAs, its reference count is
 * decremented.
 */
void unlink_anon_vmas(struct vm_area_struct *vma)
{
        struct anon_vma_chain *avc, *next;
        struct anon_vma *active_anon_vma = vma->anon_vma;

        /* Always hold mmap lock, read-lock on unmap possibly. */
        mmap_assert_locked(vma->vm_mm);

        /* Unfaulted is a no-op. */
        if (!active_anon_vma) {
                VM_WARN_ON_ONCE(!list_empty(&vma->anon_vma_chain));
                return;
        }

        anon_vma_lock_write(active_anon_vma);

        /*
         * Unlink each anon_vma chained to the VMA.  This list is ordered
         * from newest to oldest, ensuring the root anon_vma gets freed last.
         */
        list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
                struct anon_vma *anon_vma = avc->anon_vma;

                anon_vma_interval_tree_remove(avc, &anon_vma->rb_root);

                /*
                 * Leave empty anon_vmas on the list - we'll need
                 * to free them outside the lock.
                 */
                if (RB_EMPTY_ROOT(&anon_vma->rb_root.rb_root)) {
                        anon_vma->parent->num_children--;
                        continue;
                }

                list_del(&avc->same_vma);
                anon_vma_chain_free(avc);
        }

        active_anon_vma->num_active_vmas--;
        /*
         * vma would still be needed after unlink, and anon_vma will be prepared
         * when handle fault.
         */
        vma->anon_vma = NULL;
        anon_vma_unlock_write(active_anon_vma);


        /*
         * Iterate the list once more, it now only contains empty and unlinked
         * anon_vmas, destroy them. Could not do before due to __put_anon_vma()
         * needing to write-acquire the anon_vma->root->rwsem.
         */
        list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
                struct anon_vma *anon_vma = avc->anon_vma;

                VM_WARN_ON(anon_vma->num_children);
                VM_WARN_ON(anon_vma->num_active_vmas);
                put_anon_vma(anon_vma);

                list_del(&avc->same_vma);
                anon_vma_chain_free(avc);
        }
}

static void anon_vma_ctor(void *data)
{
        struct anon_vma *anon_vma = data;

        init_rwsem(&anon_vma->rwsem);
        atomic_set(&anon_vma->refcount, 0);
        anon_vma->rb_root = RB_ROOT_CACHED;
}

void __init anon_vma_init(void)
{
        anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma),
                        0, SLAB_TYPESAFE_BY_RCU|SLAB_PANIC|SLAB_ACCOUNT,
                        anon_vma_ctor);
        anon_vma_chain_cachep = KMEM_CACHE(anon_vma_chain,
                        SLAB_PANIC|SLAB_ACCOUNT);
}

/*
 * Getting a lock on a stable anon_vma from a page off the LRU is tricky!
 *
 * Since there is no serialization what so ever against folio_remove_rmap_*()
 * the best this function can do is return a refcount increased anon_vma
 * that might have been relevant to this page.
 *
 * The page might have been remapped to a different anon_vma or the anon_vma
 * returned may already be freed (and even reused).
 *
 * In case it was remapped to a different anon_vma, the new anon_vma will be a
 * child of the old anon_vma, and the anon_vma lifetime rules will therefore
 * ensure that any anon_vma obtained from the page will still be valid for as
 * long as we observe page_mapped() [ hence all those page_mapped() tests ].
 *
 * All users of this function must be very careful when walking the anon_vma
 * chain and verify that the page in question is indeed mapped in it
 * [ something equivalent to page_mapped_in_vma() ].
 *
 * Since anon_vma's slab is SLAB_TYPESAFE_BY_RCU and we know from
 * folio_remove_rmap_*() that the anon_vma pointer from page->mapping is valid
 * if there is a mapcount, we can dereference the anon_vma after observing
 * those.
 *
 * NOTE: the caller should hold folio lock when calling this.
 */
struct anon_vma *folio_get_anon_vma(const struct folio *folio)
{
        struct anon_vma *anon_vma = NULL;
        unsigned long anon_mapping;

        VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio);

        rcu_read_lock();
        anon_mapping = (unsigned long)READ_ONCE(folio->mapping);
        if ((anon_mapping & FOLIO_MAPPING_FLAGS) != FOLIO_MAPPING_ANON)
                goto out;
        if (!folio_mapped(folio))
                goto out;

        anon_vma = (struct anon_vma *) (anon_mapping - FOLIO_MAPPING_ANON);
        if (!atomic_inc_not_zero(&anon_vma->refcount)) {
                anon_vma = NULL;
                goto out;
        }

        /*
         * If this folio is still mapped, then its anon_vma cannot have been
         * freed.  But if it has been unmapped, we have no security against the
         * anon_vma structure being freed and reused (for another anon_vma:
         * SLAB_TYPESAFE_BY_RCU guarantees that - so the atomic_inc_not_zero()
         * above cannot corrupt).
         */
        if (!folio_mapped(folio)) {
                rcu_read_unlock();
                put_anon_vma(anon_vma);
                return NULL;
        }
out:
        rcu_read_unlock();

        return anon_vma;
}

/*
 * Similar to folio_get_anon_vma() except it locks the anon_vma.
 *
 * Its a little more complex as it tries to keep the fast path to a single
 * atomic op -- the trylock. If we fail the trylock, we fall back to getting a
 * reference like with folio_get_anon_vma() and then block on the mutex
 * on !rwc->try_lock case.
 */
struct anon_vma *folio_lock_anon_vma_read(const struct folio *folio,
                                          struct rmap_walk_control *rwc)
{
        struct anon_vma *anon_vma = NULL;
        struct anon_vma *root_anon_vma;
        unsigned long anon_mapping;

        VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio);

        rcu_read_lock();
        anon_mapping = (unsigned long)READ_ONCE(folio->mapping);
        if ((anon_mapping & FOLIO_MAPPING_FLAGS) != FOLIO_MAPPING_ANON)
                goto out;
        if (!folio_mapped(folio))
                goto out;

        anon_vma = (struct anon_vma *) (anon_mapping - FOLIO_MAPPING_ANON);
        root_anon_vma = READ_ONCE(anon_vma->root);
        if (down_read_trylock(&root_anon_vma->rwsem)) {
                /*
                 * If the folio is still mapped, then this anon_vma is still
                 * its anon_vma, and holding the mutex ensures that it will
                 * not go away, see anon_vma_free().
                 */
                if (!folio_mapped(folio)) {
                        up_read(&root_anon_vma->rwsem);
                        anon_vma = NULL;
                }
                goto out;
        }

        if (rwc && rwc->try_lock) {
                anon_vma = NULL;
                rwc->contended = true;
                goto out;
        }

        /* trylock failed, we got to sleep */
        if (!atomic_inc_not_zero(&anon_vma->refcount)) {
                anon_vma = NULL;
                goto out;
        }

        if (!folio_mapped(folio)) {
                rcu_read_unlock();
                put_anon_vma(anon_vma);
                return NULL;
        }

        /* we pinned the anon_vma, its safe to sleep */
        rcu_read_unlock();
        anon_vma_lock_read(anon_vma);

        if (atomic_dec_and_test(&anon_vma->refcount)) {
                /*
                 * Oops, we held the last refcount, release the lock
                 * and bail -- can't simply use put_anon_vma() because
                 * we'll deadlock on the anon_vma_lock_write() recursion.
                 */
                anon_vma_unlock_read(anon_vma);
                __put_anon_vma(anon_vma);
                anon_vma = NULL;
        }

        return anon_vma;

out:
        rcu_read_unlock();
        return anon_vma;
}

#ifdef CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
/*
 * Flush TLB entries for recently unmapped pages from remote CPUs. It is
 * important if a PTE was dirty when it was unmapped that it's flushed
 * before any IO is initiated on the page to prevent lost writes. Similarly,
 * it must be flushed before freeing to prevent data leakage.
 */
void try_to_unmap_flush(void)
{
        struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;

        if (!tlb_ubc->flush_required)
                return;

        arch_tlbbatch_flush(&tlb_ubc->arch);
        tlb_ubc->flush_required = false;
        tlb_ubc->writable = false;
}

/* Flush iff there are potentially writable TLB entries that can race with IO */
void try_to_unmap_flush_dirty(void)
{
        struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;

        if (tlb_ubc->writable)
                try_to_unmap_flush();
}

/*
 * Bits 0-14 of mm->tlb_flush_batched record pending generations.
 * Bits 16-30 of mm->tlb_flush_batched bit record flushed generations.
 */
#define TLB_FLUSH_BATCH_FLUSHED_SHIFT   16
#define TLB_FLUSH_BATCH_PENDING_MASK                    \
        ((1 << (TLB_FLUSH_BATCH_FLUSHED_SHIFT - 1)) - 1)
#define TLB_FLUSH_BATCH_PENDING_LARGE                   \
        (TLB_FLUSH_BATCH_PENDING_MASK / 2)

static void set_tlb_ubc_flush_pending(struct mm_struct *mm, pte_t pteval,
                unsigned long start, unsigned long end)
{
        struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;
        int batch;
        bool writable = pte_dirty(pteval);

        if (!pte_accessible(mm, pteval))
                return;

        arch_tlbbatch_add_pending(&tlb_ubc->arch, mm, start, end);
        tlb_ubc->flush_required = true;

        /*
         * Ensure compiler does not re-order the setting of tlb_flush_batched
         * before the PTE is cleared.
         */
        barrier();
        batch = atomic_read(&mm->tlb_flush_batched);
retry:
        if ((batch & TLB_FLUSH_BATCH_PENDING_MASK) > TLB_FLUSH_BATCH_PENDING_LARGE) {
                /*
                 * Prevent `pending' from catching up with `flushed' because of
                 * overflow.  Reset `pending' and `flushed' to be 1 and 0 if
                 * `pending' becomes large.
                 */
                if (!atomic_try_cmpxchg(&mm->tlb_flush_batched, &batch, 1))
                        goto retry;
        } else {
                atomic_inc(&mm->tlb_flush_batched);
        }

        /*
         * If the PTE was dirty then it's best to assume it's writable. The
         * caller must use try_to_unmap_flush_dirty() or try_to_unmap_flush()
         * before the page is queued for IO.
         */
        if (writable)
                tlb_ubc->writable = true;
}

/*
 * Returns true if the TLB flush should be deferred to the end of a batch of
 * unmap operations to reduce IPIs.
 */
static bool should_defer_flush(struct mm_struct *mm, enum ttu_flags flags)
{
        if (!(flags & TTU_BATCH_FLUSH))
                return false;

        return arch_tlbbatch_should_defer(mm);
}

/*
 * Reclaim unmaps pages under the PTL but do not flush the TLB prior to
 * releasing the PTL if TLB flushes are batched. It's possible for a parallel
 * operation such as mprotect or munmap to race between reclaim unmapping
 * the page and flushing the page. If this race occurs, it potentially allows
 * access to data via a stale TLB entry. Tracking all mm's that have TLB
 * batching in flight would be expensive during reclaim so instead track
 * whether TLB batching occurred in the past and if so then do a flush here
 * if required. This will cost one additional flush per reclaim cycle paid
 * by the first operation at risk such as mprotect and mumap.
 *
 * This must be called under the PTL so that an access to tlb_flush_batched
 * that is potentially a "reclaim vs mprotect/munmap/etc" race will synchronise
 * via the PTL.
 */
void flush_tlb_batched_pending(struct mm_struct *mm)
{
        int batch = atomic_read(&mm->tlb_flush_batched);
        int pending = batch & TLB_FLUSH_BATCH_PENDING_MASK;
        int flushed = batch >> TLB_FLUSH_BATCH_FLUSHED_SHIFT;

        if (pending != flushed) {
                flush_tlb_mm(mm);
                /*
                 * If the new TLB flushing is pending during flushing, leave
                 * mm->tlb_flush_batched as is, to avoid losing flushing.
                 */
                atomic_cmpxchg(&mm->tlb_flush_batched, batch,
                               pending | (pending << TLB_FLUSH_BATCH_FLUSHED_SHIFT));
        }
}
#else
static void set_tlb_ubc_flush_pending(struct mm_struct *mm, pte_t pteval,
                unsigned long start, unsigned long end)
{
}

static bool should_defer_flush(struct mm_struct *mm, enum ttu_flags flags)
{
        return false;
}
#endif /* CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH */

/**
 * page_address_in_vma - The virtual address of a page in this VMA.
 * @folio: The folio containing the page.
 * @page: The page within the folio.
 * @vma: The VMA we need to know the address in.
 *
 * Calculates the user virtual address of this page in the specified VMA.
 * It is the caller's responsibility to check the page is actually
 * within the VMA.  There may not currently be a PTE pointing at this
 * page, but if a page fault occurs at this address, this is the page
 * which will be accessed.
 *
 * Context: Caller should hold a reference to the folio.  Caller should
 * hold a lock (eg the i_mmap_lock or the mmap_lock) which keeps the
 * VMA from being altered.
 *
 * Return: The virtual address corresponding to this page in the VMA.
 */
unsigned long page_address_in_vma(const struct folio *folio,
                const struct page *page, const struct vm_area_struct *vma)
{
        if (folio_test_anon(folio)) {
                struct anon_vma *anon_vma = folio_anon_vma(folio);
                /*
                 * Note: swapoff's unuse_vma() is more efficient with this
                 * check, and needs it to match anon_vma when KSM is active.
                 */
                if (!vma->anon_vma || !anon_vma ||
                    vma->anon_vma->root != anon_vma->root)
                        return -EFAULT;
        } else if (!vma->vm_file) {
                return -EFAULT;
        } else if (vma->vm_file->f_mapping != folio->mapping) {
                return -EFAULT;
        }

        /* KSM folios don't reach here because of the !anon_vma check */
        return vma_address(vma, page_pgoff(folio, page), 1);
}

/*
 * Returns the actual pmd_t* where we expect 'address' to be mapped from, or
 * NULL if it doesn't exist.  No guarantees / checks on what the pmd_t*
 * represents.
 */
pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address)
{
        pgd_t *pgd;
        p4d_t *p4d;
        pud_t *pud;
        pmd_t *pmd = NULL;

        pgd = pgd_offset(mm, address);
        if (!pgd_present(*pgd))
                goto out;

        p4d = p4d_offset(pgd, address);
        if (!p4d_present(*p4d))
                goto out;

        pud = pud_offset(p4d, address);
        if (!pud_present(*pud))
                goto out;

        pmd = pmd_offset(pud, address);
out:
        return pmd;
}

struct folio_referenced_arg {
        int mapcount;
        int referenced;
        vm_flags_t vm_flags;
        struct mem_cgroup *memcg;
};

/*
 * arg: folio_referenced_arg will be passed
 */
static bool folio_referenced_one(struct folio *folio,
                struct vm_area_struct *vma, unsigned long address, void *arg)
{
        struct folio_referenced_arg *pra = arg;
        DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0);
        int ptes = 0, referenced = 0;
        unsigned int nr;

        while (page_vma_mapped_walk(&pvmw)) {
                address = pvmw.address;
                nr = 1;

                if (vma->vm_flags & VM_LOCKED) {
                        ptes++;
                        pra->mapcount--;

                        /* Only mlock fully mapped pages */
                        if (pvmw.pte && ptes != pvmw.nr_pages)
                                continue;

                        /*
                         * All PTEs must be protected by page table lock in
                         * order to mlock the page.
                         *
                         * If page table boundary has been cross, current ptl
                         * only protect part of ptes.
                         */
                        if (pvmw.flags & PVMW_PGTABLE_CROSSED)
                                continue;

                        /* Restore the mlock which got missed */
                        mlock_vma_folio(folio, vma);
                        page_vma_mapped_walk_done(&pvmw);
                        pra->vm_flags |= VM_LOCKED;
                        return false; /* To break the loop */
                }

                /*
                 * Skip the non-shared swapbacked folio mapped solely by
                 * the exiting or OOM-reaped process. This avoids redundant
                 * swap-out followed by an immediate unmap.
                 */
                if ((!atomic_read(&vma->vm_mm->mm_users) ||
                    check_stable_address_space(vma->vm_mm)) &&
                    folio_test_anon(folio) && folio_test_swapbacked(folio) &&
                    !folio_maybe_mapped_shared(folio)) {
                        pra->referenced = -1;
                        page_vma_mapped_walk_done(&pvmw);
                        return false;
                }

                if (lru_gen_enabled() && pvmw.pte) {
                        if (lru_gen_look_around(&pvmw))
                                referenced++;
                } else if (pvmw.pte) {
                        if (folio_test_large(folio)) {
                                unsigned long end_addr = pmd_addr_end(address, vma->vm_end);
                                unsigned int max_nr = (end_addr - address) >> PAGE_SHIFT;
                                pte_t pteval = ptep_get(pvmw.pte);

                                nr = folio_pte_batch(folio, pvmw.pte,
                                                     pteval, max_nr);
                        }

                        ptes += nr;
                        if (clear_flush_young_ptes_notify(vma, address, pvmw.pte, nr))
                                referenced++;
                        /* Skip the batched PTEs */
                        pvmw.pte += nr - 1;
                        pvmw.address += (nr - 1) * PAGE_SIZE;
                } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
                        if (pmdp_clear_flush_young_notify(vma, address,
                                                pvmw.pmd))
                                referenced++;
                } else {
                        /* unexpected pmd-mapped folio? */
                        WARN_ON_ONCE(1);
                }

                pra->mapcount -= nr;
                /*
                 * If we are sure that we batched the entire folio,
                 * we can just optimize and stop right here.
                 */
                if (ptes == pvmw.nr_pages) {
                        page_vma_mapped_walk_done(&pvmw);
                        break;
                }
        }

        if (referenced)
                folio_clear_idle(folio);
        if (folio_test_clear_young(folio))
                referenced++;

        if (referenced) {
                pra->referenced++;
                pra->vm_flags |= vma->vm_flags & ~VM_LOCKED;
        }

        if (!pra->mapcount)
                return false; /* To break the loop */

        return true;
}

static bool invalid_folio_referenced_vma(struct vm_area_struct *vma, void *arg)
{
        struct folio_referenced_arg *pra = arg;
        struct mem_cgroup *memcg = pra->memcg;

        /*
         * Ignore references from this mapping if it has no recency. If the
         * folio has been used in another mapping, we will catch it; if this
         * other mapping is already gone, the unmap path will have set the
         * referenced flag or activated the folio in zap_pte_range().
         */
        if (!vma_has_recency(vma))
                return true;

        /*
         * If we are reclaiming on behalf of a cgroup, skip counting on behalf
         * of references from different cgroups.
         */
        if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
                return true;

        return false;
}

/**
 * folio_referenced() - Test if the folio was referenced.
 * @folio: The folio to test.
 * @is_locked: Caller holds lock on the folio.
 * @memcg: target memory cgroup
 * @vm_flags: A combination of all the vma->vm_flags which referenced the folio.
 *
 * Quick test_and_clear_referenced for all mappings of a folio,
 *
 * Return: The number of mappings which referenced the folio. Return -1 if
 * the function bailed out due to rmap lock contention.
 */
int folio_referenced(struct folio *folio, int is_locked,
                     struct mem_cgroup *memcg, vm_flags_t *vm_flags)
{
        bool we_locked = false;
        struct folio_referenced_arg pra = {
                .mapcount = folio_mapcount(folio),
                .memcg = memcg,
        };
        struct rmap_walk_control rwc = {
                .rmap_one = folio_referenced_one,
                .arg = (void *)&pra,
                .anon_lock = folio_lock_anon_vma_read,
                .try_lock = true,
                .invalid_vma = invalid_folio_referenced_vma,
        };

        *vm_flags = 0;
        if (!pra.mapcount)
                return 0;

        if (!folio_raw_mapping(folio))
                return 0;

        if (!is_locked) {
                we_locked = folio_trylock(folio);
                if (!we_locked)
                        return 1;
        }

        rmap_walk(folio, &rwc);
        *vm_flags = pra.vm_flags;

        if (we_locked)
                folio_unlock(folio);

        return rwc.contended ? -1 : pra.referenced;
}

static int page_vma_mkclean_one(struct page_vma_mapped_walk *pvmw)
{
        int cleaned = 0;
        struct vm_area_struct *vma = pvmw->vma;
        struct mmu_notifier_range range;
        unsigned long address = pvmw->address;

        /*
         * We have to assume the worse case ie pmd for invalidation. Note that
         * the folio can not be freed from this function.
         */
        mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_PAGE, 0,
                                vma->vm_mm, address, vma_address_end(pvmw));
        mmu_notifier_invalidate_range_start(&range);

        while (page_vma_mapped_walk(pvmw)) {
                int ret = 0;

                address = pvmw->address;
                if (pvmw->pte) {
                        pte_t *pte = pvmw->pte;
                        pte_t entry = ptep_get(pte);

                        /*
                         * PFN swap PTEs, such as device-exclusive ones, that
                         * actually map pages are clean and not writable from a
                         * CPU perspective. The MMU notifier takes care of any
                         * device aspects.
                         */
                        if (!pte_present(entry))
                                continue;
                        if (!pte_dirty(entry) && !pte_write(entry))
                                continue;

                        flush_cache_page(vma, address, pte_pfn(entry));
                        entry = ptep_clear_flush(vma, address, pte);
                        entry = pte_wrprotect(entry);
                        entry = pte_mkclean(entry);
                        set_pte_at(vma->vm_mm, address, pte, entry);
                        ret = 1;
                } else {
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
                        pmd_t *pmd = pvmw->pmd;
                        pmd_t entry = pmdp_get(pmd);

                        /*
                         * Please see the comment above (!pte_present).
                         * A non present PMD is not writable from a CPU
                         * perspective.
                         */
                        if (!pmd_present(entry))
                                continue;
                        if (!pmd_dirty(entry) && !pmd_write(entry))
                                continue;

                        flush_cache_range(vma, address,
                                          address + HPAGE_PMD_SIZE);
                        entry = pmdp_invalidate(vma, address, pmd);
                        entry = pmd_wrprotect(entry);
                        entry = pmd_mkclean(entry);
                        set_pmd_at(vma->vm_mm, address, pmd, entry);
                        ret = 1;
#else
                        /* unexpected pmd-mapped folio? */
                        WARN_ON_ONCE(1);
#endif
                }

                if (ret)
                        cleaned++;
        }

        mmu_notifier_invalidate_range_end(&range);

        return cleaned;
}

static bool page_mkclean_one(struct folio *folio, struct vm_area_struct *vma,
                             unsigned long address, void *arg)
{
        DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, PVMW_SYNC);
        int *cleaned = arg;

        *cleaned += page_vma_mkclean_one(&pvmw);

        return true;
}

static bool invalid_mkclean_vma(struct vm_area_struct *vma, void *arg)
{
        if (vma->vm_flags & VM_SHARED)
                return false;

        return true;
}

int folio_mkclean(struct folio *folio)
{
        int cleaned = 0;
        struct address_space *mapping;
        struct rmap_walk_control rwc = {
                .arg = (void *)&cleaned,
                .rmap_one = page_mkclean_one,
                .invalid_vma = invalid_mkclean_vma,
        };

        BUG_ON(!folio_test_locked(folio));

        if (!folio_mapped(folio))
                return 0;

        mapping = folio_mapping(folio);
        if (!mapping)
                return 0;

        rmap_walk(folio, &rwc);

        return cleaned;
}
EXPORT_SYMBOL_GPL(folio_mkclean);

struct wrprotect_file_state {
        int cleaned;
        pgoff_t pgoff;
        unsigned long pfn;
        unsigned long nr_pages;
};

static bool mapping_wrprotect_range_one(struct folio *folio,
                struct vm_area_struct *vma, unsigned long address, void *arg)
{
        struct wrprotect_file_state *state = (struct wrprotect_file_state *)arg;
        struct page_vma_mapped_walk pvmw = {
                .pfn            = state->pfn,
                .nr_pages       = state->nr_pages,
                .pgoff          = state->pgoff,
                .vma            = vma,
                .address        = address,
                .flags          = PVMW_SYNC,
        };

        state->cleaned += page_vma_mkclean_one(&pvmw);

        return true;
}

static void __rmap_walk_file(struct folio *folio, struct address_space *mapping,
                             pgoff_t pgoff_start, unsigned long nr_pages,
                             struct rmap_walk_control *rwc, bool locked);

/**
 * mapping_wrprotect_range() - Write-protect all mappings in a specified range.
 *
 * @mapping:    The mapping whose reverse mapping should be traversed.
 * @pgoff:      The page offset at which @pfn is mapped within @mapping.
 * @pfn:        The PFN of the page mapped in @mapping at @pgoff.
 * @nr_pages:   The number of physically contiguous base pages spanned.
 *
 * Traverses the reverse mapping, finding all VMAs which contain a shared
 * mapping of the pages in the specified range in @mapping, and write-protects
 * them (that is, updates the page tables to mark the mappings read-only such
 * that a write protection fault arises when the mappings are written to).
 *
 * The @pfn value need not refer to a folio, but rather can reference a kernel
 * allocation which is mapped into userland. We therefore do not require that
 * the page maps to a folio with a valid mapping or index field, rather the
 * caller specifies these in @mapping and @pgoff.
 *
 * Return: the number of write-protected PTEs, or an error.
 */
int mapping_wrprotect_range(struct address_space *mapping, pgoff_t pgoff,
                unsigned long pfn, unsigned long nr_pages)
{
        struct wrprotect_file_state state = {
                .cleaned = 0,
                .pgoff = pgoff,
                .pfn = pfn,
                .nr_pages = nr_pages,
        };
        struct rmap_walk_control rwc = {
                .arg = (void *)&state,
                .rmap_one = mapping_wrprotect_range_one,
                .invalid_vma = invalid_mkclean_vma,
        };

        if (!mapping)
                return 0;

        __rmap_walk_file(/* folio = */NULL, mapping, pgoff, nr_pages, &rwc,
                         /* locked = */false);

        return state.cleaned;
}
EXPORT_SYMBOL_GPL(mapping_wrprotect_range);

/**
 * pfn_mkclean_range - Cleans the PTEs (including PMDs) mapped with range of
 *                     [@pfn, @pfn + @nr_pages) at the specific offset (@pgoff)
 *                     within the @vma of shared mappings. And since clean PTEs
 *                     should also be readonly, write protects them too.
 * @pfn: start pfn.
 * @nr_pages: number of physically contiguous pages srarting with @pfn.
 * @pgoff: page offset that the @pfn mapped with.
 * @vma: vma that @pfn mapped within.
 *
 * Returns the number of cleaned PTEs (including PMDs).
 */
int pfn_mkclean_range(unsigned long pfn, unsigned long nr_pages, pgoff_t pgoff,
                      struct vm_area_struct *vma)
{
        struct page_vma_mapped_walk pvmw = {
                .pfn            = pfn,
                .nr_pages       = nr_pages,
                .pgoff          = pgoff,
                .vma            = vma,
                .flags          = PVMW_SYNC,
        };

        if (invalid_mkclean_vma(vma, NULL))
                return 0;

        pvmw.address = vma_address(vma, pgoff, nr_pages);
        VM_BUG_ON_VMA(pvmw.address == -EFAULT, vma);

        return page_vma_mkclean_one(&pvmw);
}

static void __folio_mod_stat(struct folio *folio, int nr, int nr_pmdmapped)
{
        int idx;

        if (nr) {
                idx = folio_test_anon(folio) ? NR_ANON_MAPPED : NR_FILE_MAPPED;
                lruvec_stat_mod_folio(folio, idx, nr);
        }
        if (nr_pmdmapped) {
                if (folio_test_anon(folio)) {
                        idx = NR_ANON_THPS;
                        lruvec_stat_mod_folio(folio, idx, nr_pmdmapped);
                } else {
                        /* NR_*_PMDMAPPED are not maintained per-memcg */
                        idx = folio_test_swapbacked(folio) ?
                                NR_SHMEM_PMDMAPPED : NR_FILE_PMDMAPPED;
                        __mod_node_page_state(folio_pgdat(folio), idx,
                                              nr_pmdmapped);
                }
        }
}

static __always_inline void __folio_add_rmap(struct folio *folio,
                struct page *page, int nr_pages, struct vm_area_struct *vma,
                enum pgtable_level level)
{
        atomic_t *mapped = &folio->_nr_pages_mapped;
        const int orig_nr_pages = nr_pages;
        int first = 0, nr = 0, nr_pmdmapped = 0;

        __folio_rmap_sanity_checks(folio, page, nr_pages, level);

        switch (level) {
        case PGTABLE_LEVEL_PTE:
                if (!folio_test_large(folio)) {
                        nr = atomic_inc_and_test(&folio->_mapcount);
                        break;
                }

                if (IS_ENABLED(CONFIG_NO_PAGE_MAPCOUNT)) {
                        nr = folio_add_return_large_mapcount(folio, orig_nr_pages, vma);
                        if (nr == orig_nr_pages)
                                /* Was completely unmapped. */
                                nr = folio_large_nr_pages(folio);
                        else
                                nr = 0;
                        break;
                }

                do {
                        first += atomic_inc_and_test(&page->_mapcount);
                } while (page++, --nr_pages > 0);

                if (first &&
                    atomic_add_return_relaxed(first, mapped) < ENTIRELY_MAPPED)
                        nr = first;

                folio_add_large_mapcount(folio, orig_nr_pages, vma);
                break;
        case PGTABLE_LEVEL_PMD:
        case PGTABLE_LEVEL_PUD:
                first = atomic_inc_and_test(&folio->_entire_mapcount);
                if (IS_ENABLED(CONFIG_NO_PAGE_MAPCOUNT)) {
                        if (level == PGTABLE_LEVEL_PMD && first)
                                nr_pmdmapped = folio_large_nr_pages(folio);
                        nr = folio_inc_return_large_mapcount(folio, vma);
                        if (nr == 1)
                                /* Was completely unmapped. */
                                nr = folio_large_nr_pages(folio);
                        else
                                nr = 0;
                        break;
                }

                if (first) {
                        nr = atomic_add_return_relaxed(ENTIRELY_MAPPED, mapped);
                        if (likely(nr < ENTIRELY_MAPPED + ENTIRELY_MAPPED)) {
                                nr_pages = folio_large_nr_pages(folio);
                                /*
                                 * We only track PMD mappings of PMD-sized
                                 * folios separately.
                                 */
                                if (level == PGTABLE_LEVEL_PMD)
                                        nr_pmdmapped = nr_pages;
                                nr = nr_pages - (nr & FOLIO_PAGES_MAPPED);
                                /* Raced ahead of a remove and another add? */
                                if (unlikely(nr < 0))
                                        nr = 0;
                        } else {
                                /* Raced ahead of a remove of ENTIRELY_MAPPED */
                                nr = 0;
                        }
                }
                folio_inc_large_mapcount(folio, vma);
                break;
        default:
                BUILD_BUG();
        }
        __folio_mod_stat(folio, nr, nr_pmdmapped);
}

/**
 * folio_move_anon_rmap - move a folio to our anon_vma
 * @folio:      The folio to move to our anon_vma
 * @vma:        The vma the folio belongs to
 *
 * When a folio belongs exclusively to one process after a COW event,
 * that folio can be moved into the anon_vma that belongs to just that
 * process, so the rmap code will not search the parent or sibling processes.
 */
void folio_move_anon_rmap(struct folio *folio, struct vm_area_struct *vma)
{
        void *anon_vma = vma->anon_vma;

        VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
        VM_BUG_ON_VMA(!anon_vma, vma);

        anon_vma += FOLIO_MAPPING_ANON;
        /*
         * Ensure that anon_vma and the FOLIO_MAPPING_ANON bit are written
         * simultaneously, so a concurrent reader (eg folio_referenced()'s
         * folio_test_anon()) will not see one without the other.
         */
        WRITE_ONCE(folio->mapping, anon_vma);
}

/**
 * __folio_set_anon - set up a new anonymous rmap for a folio
 * @folio:      The folio to set up the new anonymous rmap for.
 * @vma:        VM area to add the folio to.
 * @address:    User virtual address of the mapping
 * @exclusive:  Whether the folio is exclusive to the process.
 */
static void __folio_set_anon(struct folio *folio, struct vm_area_struct *vma,
                             unsigned long address, bool exclusive)
{
        struct anon_vma *anon_vma = vma->anon_vma;

        BUG_ON(!anon_vma);

        /*
         * If the folio isn't exclusive to this vma, we must use the _oldest_
         * possible anon_vma for the folio mapping!
         */
        if (!exclusive)
                anon_vma = anon_vma->root;

        /*
         * page_idle does a lockless/optimistic rmap scan on folio->mapping.
         * Make sure the compiler doesn't split the stores of anon_vma and
         * the FOLIO_MAPPING_ANON type identifier, otherwise the rmap code
         * could mistake the mapping for a struct address_space and crash.
         */
        anon_vma = (void *) anon_vma + FOLIO_MAPPING_ANON;
        WRITE_ONCE(folio->mapping, (struct address_space *) anon_vma);
        folio->index = linear_page_index(vma, address);
}

/**
 * __page_check_anon_rmap - sanity check anonymous rmap addition
 * @folio:      The folio containing @page.
 * @page:       the page to check the mapping of
 * @vma:        the vm area in which the mapping is added
 * @address:    the user virtual address mapped
 */
static void __page_check_anon_rmap(const struct folio *folio,
                const struct page *page, struct vm_area_struct *vma,
                unsigned long address)
{
        /*
         * The page's anon-rmap details (mapping and index) are guaranteed to
         * be set up correctly at this point.
         *
         * We have exclusion against folio_add_anon_rmap_*() because the caller
         * always holds the page locked.
         *
         * We have exclusion against folio_add_new_anon_rmap because those pages
         * are initially only visible via the pagetables, and the pte is locked
         * over the call to folio_add_new_anon_rmap.
         */
        VM_BUG_ON_FOLIO(folio_anon_vma(folio)->root != vma->anon_vma->root,
                        folio);
        VM_BUG_ON_PAGE(page_pgoff(folio, page) != linear_page_index(vma, address),
                       page);
}

static __always_inline void __folio_add_anon_rmap(struct folio *folio,
                struct page *page, int nr_pages, struct vm_area_struct *vma,
                unsigned long address, rmap_t flags, enum pgtable_level level)
{
        int i;

        VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);

        __folio_add_rmap(folio, page, nr_pages, vma, level);

        if (likely(!folio_test_ksm(folio)))
                __page_check_anon_rmap(folio, page, vma, address);

        if (flags & RMAP_EXCLUSIVE) {
                switch (level) {
                case PGTABLE_LEVEL_PTE:
                        for (i = 0; i < nr_pages; i++)
                                SetPageAnonExclusive(page + i);
                        break;
                case PGTABLE_LEVEL_PMD:
                        SetPageAnonExclusive(page);
                        break;
                case PGTABLE_LEVEL_PUD:
                        /*
                         * Keep the compiler happy, we don't support anonymous
                         * PUD mappings.
                         */
                        WARN_ON_ONCE(1);
                        break;
                default:
                        BUILD_BUG();
                }
        }

        VM_WARN_ON_FOLIO(!folio_test_large(folio) && PageAnonExclusive(page) &&
                         atomic_read(&folio->_mapcount) > 0, folio);
        for (i = 0; i < nr_pages; i++) {
                struct page *cur_page = page + i;

                VM_WARN_ON_FOLIO(folio_test_large(folio) &&
                                 folio_entire_mapcount(folio) > 1 &&
                                 PageAnonExclusive(cur_page), folio);
                if (IS_ENABLED(CONFIG_NO_PAGE_MAPCOUNT))
                        continue;

                /*
                 * While PTE-mapping a THP we have a PMD and a PTE
                 * mapping.
                 */
                VM_WARN_ON_FOLIO(atomic_read(&cur_page->_mapcount) > 0 &&
                                 PageAnonExclusive(cur_page), folio);
        }

        /*
         * Only mlock it if the folio is fully mapped to the VMA.
         *
         * Partially mapped folios can be split on reclaim and part outside
         * of mlocked VMA can be evicted or freed.
         */
        if (folio_nr_pages(folio) == nr_pages)
                mlock_vma_folio(folio, vma);
}

/**
 * folio_add_anon_rmap_ptes - add PTE mappings to a page range of an anon folio
 * @folio:      The folio to add the mappings to
 * @page:       The first page to add
 * @nr_pages:   The number of pages which will be mapped
 * @vma:        The vm area in which the mappings are added
 * @address:    The user virtual address of the first page to map
 * @flags:      The rmap flags
 *
 * The page range of folio is defined by [first_page, first_page + nr_pages)
 *
 * The caller needs to hold the page table lock, and the page must be locked in
 * the anon_vma case: to serialize mapping,index checking after setting,
 * and to ensure that an anon folio is not being upgraded racily to a KSM folio
 * (but KSM folios are never downgraded).
 */
void folio_add_anon_rmap_ptes(struct folio *folio, struct page *page,
                int nr_pages, struct vm_area_struct *vma, unsigned long address,
                rmap_t flags)
{
        __folio_add_anon_rmap(folio, page, nr_pages, vma, address, flags,
                              PGTABLE_LEVEL_PTE);
}

/**
 * folio_add_anon_rmap_pmd - add a PMD mapping to a page range of an anon folio
 * @folio:      The folio to add the mapping to
 * @page:       The first page to add
 * @vma:        The vm area in which the mapping is added
 * @address:    The user virtual address of the first page to map
 * @flags:      The rmap flags
 *
 * The page range of folio is defined by [first_page, first_page + HPAGE_PMD_NR)
 *
 * The caller needs to hold the page table lock, and the page must be locked in
 * the anon_vma case: to serialize mapping,index checking after setting.
 */
void folio_add_anon_rmap_pmd(struct folio *folio, struct page *page,
                struct vm_area_struct *vma, unsigned long address, rmap_t flags)
{
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
        __folio_add_anon_rmap(folio, page, HPAGE_PMD_NR, vma, address, flags,
                              PGTABLE_LEVEL_PMD);
#else
        WARN_ON_ONCE(true);
#endif
}

/**
 * folio_add_new_anon_rmap - Add mapping to a new anonymous folio.
 * @folio:      The folio to add the mapping to.
 * @vma:        the vm area in which the mapping is added
 * @address:    the user virtual address mapped
 * @flags:      The rmap flags
 *
 * Like folio_add_anon_rmap_*() but must only be called on *new* folios.
 * This means the inc-and-test can be bypassed.
 * The folio doesn't necessarily need to be locked while it's exclusive
 * unless two threads map it concurrently. However, the folio must be
 * locked if it's shared.
 *
 * If the folio is pmd-mappable, it is accounted as a THP.
 */
void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma,
                unsigned long address, rmap_t flags)
{
        const bool exclusive = flags & RMAP_EXCLUSIVE;
        int nr = 1, nr_pmdmapped = 0;

        VM_WARN_ON_FOLIO(folio_test_hugetlb(folio), folio);
        VM_WARN_ON_FOLIO(!exclusive && !folio_test_locked(folio), folio);

        /*
         * VM_DROPPABLE mappings don't swap; instead they're just dropped when
         * under memory pressure.
         */
        if (!folio_test_swapbacked(folio) && !(vma->vm_flags & VM_DROPPABLE))
                __folio_set_swapbacked(folio);
        __folio_set_anon(folio, vma, address, exclusive);

        if (likely(!folio_test_large(folio))) {
                /* increment count (starts at -1) */
                atomic_set(&folio->_mapcount, 0);
                if (exclusive)
                        SetPageAnonExclusive(&folio->page);
        } else if (!folio_test_pmd_mappable(folio)) {
                int i;

                nr = folio_large_nr_pages(folio);
                for (i = 0; i < nr; i++) {
                        struct page *page = folio_page(folio, i);

                        if (IS_ENABLED(CONFIG_PAGE_MAPCOUNT))
                                /* increment count (starts at -1) */
                                atomic_set(&page->_mapcount, 0);
                        if (exclusive)
                                SetPageAnonExclusive(page);
                }

                folio_set_large_mapcount(folio, nr, vma);
                if (IS_ENABLED(CONFIG_PAGE_MAPCOUNT))
                        atomic_set(&folio->_nr_pages_mapped, nr);
        } else {
                nr = folio_large_nr_pages(folio);
                /* increment count (starts at -1) */
                atomic_set(&folio->_entire_mapcount, 0);
                folio_set_large_mapcount(folio, 1, vma);
                if (IS_ENABLED(CONFIG_PAGE_MAPCOUNT))
                        atomic_set(&folio->_nr_pages_mapped, ENTIRELY_MAPPED);
                if (exclusive)
                        SetPageAnonExclusive(&folio->page);
                nr_pmdmapped = nr;
        }

        VM_WARN_ON_ONCE(address < vma->vm_start ||
                        address + (nr << PAGE_SHIFT) > vma->vm_end);

        __folio_mod_stat(folio, nr, nr_pmdmapped);
        mod_mthp_stat(folio_order(folio), MTHP_STAT_NR_ANON, 1);
}

static __always_inline void __folio_add_file_rmap(struct folio *folio,
                struct page *page, int nr_pages, struct vm_area_struct *vma,
                enum pgtable_level level)
{
        VM_WARN_ON_FOLIO(folio_test_anon(folio), folio);

        __folio_add_rmap(folio, page, nr_pages, vma, level);

        /*
         * Only mlock it if the folio is fully mapped to the VMA.
         *
         * Partially mapped folios can be split on reclaim and part outside
         * of mlocked VMA can be evicted or freed.
         */
        if (folio_nr_pages(folio) == nr_pages)
                mlock_vma_folio(folio, vma);
}

/**
 * folio_add_file_rmap_ptes - add PTE mappings to a page range of a folio
 * @folio:      The folio to add the mappings to
 * @page:       The first page to add
 * @nr_pages:   The number of pages that will be mapped using PTEs
 * @vma:        The vm area in which the mappings are added
 *
 * The page range of the folio is defined by [page, page + nr_pages)
 *
 * The caller needs to hold the page table lock.
 */
void folio_add_file_rmap_ptes(struct folio *folio, struct page *page,
                int nr_pages, struct vm_area_struct *vma)
{
        __folio_add_file_rmap(folio, page, nr_pages, vma, PGTABLE_LEVEL_PTE);
}

/**
 * folio_add_file_rmap_pmd - add a PMD mapping to a page range of a folio
 * @folio:      The folio to add the mapping to
 * @page:       The first page to add
 * @vma:        The vm area in which the mapping is added
 *
 * The page range of the folio is defined by [page, page + HPAGE_PMD_NR)
 *
 * The caller needs to hold the page table lock.
 */
void folio_add_file_rmap_pmd(struct folio *folio, struct page *page,
                struct vm_area_struct *vma)
{
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
        __folio_add_file_rmap(folio, page, HPAGE_PMD_NR, vma, PGTABLE_LEVEL_PMD);
#else
        WARN_ON_ONCE(true);
#endif
}

/**
 * folio_add_file_rmap_pud - add a PUD mapping to a page range of a folio
 * @folio:      The folio to add the mapping to
 * @page:       The first page to add
 * @vma:        The vm area in which the mapping is added
 *
 * The page range of the folio is defined by [page, page + HPAGE_PUD_NR)
 *
 * The caller needs to hold the page table lock.
 */
void folio_add_file_rmap_pud(struct folio *folio, struct page *page,
                struct vm_area_struct *vma)
{
#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && \
        defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
        __folio_add_file_rmap(folio, page, HPAGE_PUD_NR, vma, PGTABLE_LEVEL_PUD);
#else
        WARN_ON_ONCE(true);
#endif
}

static __always_inline void __folio_remove_rmap(struct folio *folio,
                struct page *page, int nr_pages, struct vm_area_struct *vma,
                enum pgtable_level level)
{
        atomic_t *mapped = &folio->_nr_pages_mapped;
        int last = 0, nr = 0, nr_pmdmapped = 0;
        bool partially_mapped = false;

        __folio_rmap_sanity_checks(folio, page, nr_pages, level);

        switch (level) {
        case PGTABLE_LEVEL_PTE:
                if (!folio_test_large(folio)) {
                        nr = atomic_add_negative(-1, &folio->_mapcount);
                        break;
                }

                if (IS_ENABLED(CONFIG_NO_PAGE_MAPCOUNT)) {
                        nr = folio_sub_return_large_mapcount(folio, nr_pages, vma);
                        if (!nr) {
                                /* Now completely unmapped. */
                                nr = folio_large_nr_pages(folio);
                        } else {
                                partially_mapped = nr < folio_large_nr_pages(folio) &&
                                                   !folio_entire_mapcount(folio);
                                nr = 0;
                        }
                        break;
                }

                folio_sub_large_mapcount(folio, nr_pages, vma);
                do {
                        last += atomic_add_negative(-1, &page->_mapcount);
                } while (page++, --nr_pages > 0);

                if (last &&
                    atomic_sub_return_relaxed(last, mapped) < ENTIRELY_MAPPED)
                        nr = last;

                partially_mapped = nr && atomic_read(mapped);
                break;
        case PGTABLE_LEVEL_PMD:
        case PGTABLE_LEVEL_PUD:
                if (IS_ENABLED(CONFIG_NO_PAGE_MAPCOUNT)) {
                        last = atomic_add_negative(-1, &folio->_entire_mapcount);
                        if (level == PGTABLE_LEVEL_PMD && last)
                                nr_pmdmapped = folio_large_nr_pages(folio);
                        nr = folio_dec_return_large_mapcount(folio, vma);
                        if (!nr) {
                                /* Now completely unmapped. */
                                nr = folio_large_nr_pages(folio);
                        } else {
                                partially_mapped = last &&
                                                   nr < folio_large_nr_pages(folio);
                                nr = 0;
                        }
                        break;
                }

                folio_dec_large_mapcount(folio, vma);
                last = atomic_add_negative(-1, &folio->_entire_mapcount);
                if (last) {
                        nr = atomic_sub_return_relaxed(ENTIRELY_MAPPED, mapped);
                        if (likely(nr < ENTIRELY_MAPPED)) {
                                nr_pages = folio_large_nr_pages(folio);
                                if (level == PGTABLE_LEVEL_PMD)
                                        nr_pmdmapped = nr_pages;
                                nr = nr_pages - nr;
                                /* Raced ahead of another remove and an add? */
                                if (unlikely(nr < 0))
                                        nr = 0;
                        } else {
                                /* An add of ENTIRELY_MAPPED raced ahead */
                                nr = 0;
                        }
                }

                partially_mapped = nr && nr < nr_pmdmapped;
                break;
        default:
                BUILD_BUG();
        }

        /*
         * Queue anon large folio for deferred split if at least one page of
         * the folio is unmapped and at least one page is still mapped.
         *
         * Check partially_mapped first to ensure it is a large folio.
         *
         * Device private folios do not support deferred splitting and
         * shrinker based scanning of the folios to free.
         */
        if (partially_mapped && folio_test_anon(folio) &&
            !folio_test_partially_mapped(folio) &&
            !folio_is_device_private(folio))
                deferred_split_folio(folio, true);

        __folio_mod_stat(folio, -nr, -nr_pmdmapped);

        /*
         * It would be tidy to reset folio_test_anon mapping when fully
         * unmapped, but that might overwrite a racing folio_add_anon_rmap_*()
         * which increments mapcount after us but sets mapping before us:
         * so leave the reset to free_pages_prepare, and remember that
         * it's only reliable while mapped.
         */

        munlock_vma_folio(folio, vma);
}

/**
 * folio_remove_rmap_ptes - remove PTE mappings from a page range of a folio
 * @folio:      The folio to remove the mappings from
 * @page:       The first page to remove
 * @nr_pages:   The number of pages that will be removed from the mapping
 * @vma:        The vm area from which the mappings are removed
 *
 * The page range of the folio is defined by [page, page + nr_pages)
 *
 * The caller needs to hold the page table lock.
 */
void folio_remove_rmap_ptes(struct folio *folio, struct page *page,
                int nr_pages, struct vm_area_struct *vma)
{
        __folio_remove_rmap(folio, page, nr_pages, vma, PGTABLE_LEVEL_PTE);
}

/**
 * folio_remove_rmap_pmd - remove a PMD mapping from a page range of a folio
 * @folio:      The folio to remove the mapping from
 * @page:       The first page to remove
 * @vma:        The vm area from which the mapping is removed
 *
 * The page range of the folio is defined by [page, page + HPAGE_PMD_NR)
 *
 * The caller needs to hold the page table lock.
 */
void folio_remove_rmap_pmd(struct folio *folio, struct page *page,
                struct vm_area_struct *vma)
{
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
        __folio_remove_rmap(folio, page, HPAGE_PMD_NR, vma, PGTABLE_LEVEL_PMD);
#else
        WARN_ON_ONCE(true);
#endif
}

/**
 * folio_remove_rmap_pud - remove a PUD mapping from a page range of a folio
 * @folio:      The folio to remove the mapping from
 * @page:       The first page to remove
 * @vma:        The vm area from which the mapping is removed
 *
 * The page range of the folio is defined by [page, page + HPAGE_PUD_NR)
 *
 * The caller needs to hold the page table lock.
 */
void folio_remove_rmap_pud(struct folio *folio, struct page *page,
                struct vm_area_struct *vma)
{
#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && \
        defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
        __folio_remove_rmap(folio, page, HPAGE_PUD_NR, vma, PGTABLE_LEVEL_PUD);
#else
        WARN_ON_ONCE(true);
#endif
}

static inline unsigned int folio_unmap_pte_batch(struct folio *folio,
                        struct page_vma_mapped_walk *pvmw,
                        enum ttu_flags flags, pte_t pte)
{
        unsigned long end_addr, addr = pvmw->address;
        struct vm_area_struct *vma = pvmw->vma;
        unsigned int max_nr;

        if (flags & TTU_HWPOISON)
                return 1;
        if (!folio_test_large(folio))
                return 1;

        /* We may only batch within a single VMA and a single page table. */
        end_addr = pmd_addr_end(addr, vma->vm_end);
        max_nr = (end_addr - addr) >> PAGE_SHIFT;

        /* We only support lazyfree or file folios batching for now ... */
        if (folio_test_anon(folio) && folio_test_swapbacked(folio))
                return 1;

        if (pte_unused(pte))
                return 1;

        if (userfaultfd_wp(vma))
                return 1;

        /*
         * If unmap fails, we need to restore the ptes. To avoid accidentally
         * upgrading write permissions for ptes that were not originally
         * writable, and to avoid losing the soft-dirty bit, use the
         * appropriate FPB flags.
         */
        return folio_pte_batch_flags(folio, vma, pvmw->pte, &pte, max_nr,
                                     FPB_RESPECT_WRITE | FPB_RESPECT_SOFT_DIRTY);
}

/*
 * @arg: enum ttu_flags will be passed to this argument
 */
static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
                     unsigned long address, void *arg)
{
        struct mm_struct *mm = vma->vm_mm;
        DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0);
        bool anon_exclusive, ret = true;
        pte_t pteval;
        struct page *subpage;
        struct mmu_notifier_range range;
        enum ttu_flags flags = (enum ttu_flags)(long)arg;
        unsigned long nr_pages = 1, end_addr;
        unsigned long pfn;
        unsigned long hsz = 0;
        int ptes = 0;

        /*
         * When racing against e.g. zap_pte_range() on another cpu,
         * in between its ptep_get_and_clear_full() and folio_remove_rmap_*(),
         * try_to_unmap() may return before page_mapped() has become false,
         * if page table locking is skipped: use TTU_SYNC to wait for that.
         */
        if (flags & TTU_SYNC)
                pvmw.flags = PVMW_SYNC;

        /*
         * For THP, we have to assume the worse case ie pmd for invalidation.
         * For hugetlb, it could be much worse if we need to do pud
         * invalidation in the case of pmd sharing.
         *
         * Note that the folio can not be freed in this function as call of
         * try_to_unmap() must hold a reference on the folio.
         */
        range.end = vma_address_end(&pvmw);
        mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma->vm_mm,
                                address, range.end);
        if (folio_test_hugetlb(folio)) {
                /*
                 * If sharing is possible, start and end will be adjusted
                 * accordingly.
                 */
                adjust_range_if_pmd_sharing_possible(vma, &range.start,
                                                     &range.end);

                /* We need the huge page size for set_huge_pte_at() */
                hsz = huge_page_size(hstate_vma(vma));
        }
        mmu_notifier_invalidate_range_start(&range);

        while (page_vma_mapped_walk(&pvmw)) {
                /*
                 * If the folio is in an mlock()d vma, we must not swap it out.
                 */
                if (!(flags & TTU_IGNORE_MLOCK) &&
                    (vma->vm_flags & VM_LOCKED)) {
                        ptes++;

                        /*
                         * Set 'ret' to indicate the page cannot be unmapped.
                         *
                         * Do not jump to walk_abort immediately as additional
                         * iteration might be required to detect fully mapped
                         * folio an mlock it.
                         */
                        ret = false;

                        /* Only mlock fully mapped pages */
                        if (pvmw.pte && ptes != pvmw.nr_pages)
                                continue;

                        /*
                         * All PTEs must be protected by page table lock in
                         * order to mlock the page.
                         *
                         * If page table boundary has been cross, current ptl
                         * only protect part of ptes.
                         */
                        if (pvmw.flags & PVMW_PGTABLE_CROSSED)
                                goto walk_done;

                        /* Restore the mlock which got missed */
                        mlock_vma_folio(folio, vma);
                        goto walk_done;
                }

                if (!pvmw.pte) {
                        if (folio_test_anon(folio) && !folio_test_swapbacked(folio)) {
                                if (unmap_huge_pmd_locked(vma, pvmw.address, pvmw.pmd, folio))
                                        goto walk_done;
                                /*
                                 * unmap_huge_pmd_locked has either already marked
                                 * the folio as swap-backed or decided to retain it
                                 * due to GUP or speculative references.
                                 */
                                goto walk_abort;
                        }

                        if (flags & TTU_SPLIT_HUGE_PMD) {
                                /*
                                 * We temporarily have to drop the PTL and
                                 * restart so we can process the PTE-mapped THP.
                                 */
                                split_huge_pmd_locked(vma, pvmw.address,
                                                      pvmw.pmd, false);
                                flags &= ~TTU_SPLIT_HUGE_PMD;
                                page_vma_mapped_walk_restart(&pvmw);
                                continue;
                        }
                }

                /* Unexpected PMD-mapped THP? */
                VM_BUG_ON_FOLIO(!pvmw.pte, folio);

                /*
                 * Handle PFN swap PTEs, such as device-exclusive ones, that
                 * actually map pages.
                 */
                pteval = ptep_get(pvmw.pte);
                if (likely(pte_present(pteval))) {
                        pfn = pte_pfn(pteval);
                } else {
                        const softleaf_t entry = softleaf_from_pte(pteval);

                        pfn = softleaf_to_pfn(entry);
                        VM_WARN_ON_FOLIO(folio_test_hugetlb(folio), folio);
                }

                subpage = folio_page(folio, pfn - folio_pfn(folio));
                address = pvmw.address;
                anon_exclusive = folio_test_anon(folio) &&
                                 PageAnonExclusive(subpage);

                if (folio_test_hugetlb(folio)) {
                        bool anon = folio_test_anon(folio);

                        /*
                         * The try_to_unmap() is only passed a hugetlb page
                         * in the case where the hugetlb page is poisoned.
                         */
                        VM_BUG_ON_PAGE(!PageHWPoison(subpage), subpage);
                        /*
                         * huge_pmd_unshare may unmap an entire PMD page.
                         * There is no way of knowing exactly which PMDs may
                         * be cached for this mm, so we must flush them all.
                         * start/end were already adjusted above to cover this
                         * range.
                         */
                        flush_cache_range(vma, range.start, range.end);

                        /*
                         * To call huge_pmd_unshare, i_mmap_rwsem must be
                         * held in write mode.  Caller needs to explicitly
                         * do this outside rmap routines.
                         *
                         * We also must hold hugetlb vma_lock in write mode.
                         * Lock order dictates acquiring vma_lock BEFORE
                         * i_mmap_rwsem.  We can only try lock here and fail
                         * if unsuccessful.
                         */
                        if (!anon) {
                                struct mmu_gather tlb;

                                VM_BUG_ON(!(flags & TTU_RMAP_LOCKED));
                                if (!hugetlb_vma_trylock_write(vma))
                                        goto walk_abort;

                                tlb_gather_mmu_vma(&tlb, vma);
                                if (huge_pmd_unshare(&tlb, vma, address, pvmw.pte)) {
                                        hugetlb_vma_unlock_write(vma);
                                        huge_pmd_unshare_flush(&tlb, vma);
                                        tlb_finish_mmu(&tlb);
                                        /*
                                         * The PMD table was unmapped,
                                         * consequently unmapping the folio.
                                         */
                                        goto walk_done;
                                }
                                hugetlb_vma_unlock_write(vma);
                                tlb_finish_mmu(&tlb);
                        }
                        pteval = huge_ptep_clear_flush(vma, address, pvmw.pte);
                        if (pte_dirty(pteval))
                                folio_mark_dirty(folio);
                } else if (likely(pte_present(pteval))) {
                        nr_pages = folio_unmap_pte_batch(folio, &pvmw, flags, pteval);
                        end_addr = address + nr_pages * PAGE_SIZE;
                        flush_cache_range(vma, address, end_addr);

                        /* Nuke the page table entry. */
                        pteval = get_and_clear_ptes(mm, address, pvmw.pte, nr_pages);
                        /*
                         * We clear the PTE but do not flush so potentially
                         * a remote CPU could still be writing to the folio.
                         * If the entry was previously clean then the
                         * architecture must guarantee that a clear->dirty
                         * transition on a cached TLB entry is written through
                         * and traps if the PTE is unmapped.
                         */
                        if (should_defer_flush(mm, flags))
                                set_tlb_ubc_flush_pending(mm, pteval, address, end_addr);
                        else
                                flush_tlb_range(vma, address, end_addr);
                        if (pte_dirty(pteval))
                                folio_mark_dirty(folio);
                } else {
                        pte_clear(mm, address, pvmw.pte);
                }

                /*
                 * Now the pte is cleared. If this pte was uffd-wp armed,
                 * we may want to replace a none pte with a marker pte if
                 * it's file-backed, so we don't lose the tracking info.
                 */
                pte_install_uffd_wp_if_needed(vma, address, pvmw.pte, pteval);

                /* Update high watermark before we lower rss */
                update_hiwater_rss(mm);

                if (PageHWPoison(subpage) && (flags & TTU_HWPOISON)) {
                        pteval = swp_entry_to_pte(make_hwpoison_entry(subpage));
                        if (folio_test_hugetlb(folio)) {
                                hugetlb_count_sub(folio_nr_pages(folio), mm);
                                set_huge_pte_at(mm, address, pvmw.pte, pteval,
                                                hsz);
                        } else {
                                dec_mm_counter(mm, mm_counter(folio));
                                set_pte_at(mm, address, pvmw.pte, pteval);
                        }
                } else if (likely(pte_present(pteval)) && pte_unused(pteval) &&
                           !userfaultfd_armed(vma)) {
                        /*
                         * The guest indicated that the page content is of no
                         * interest anymore. Simply discard the pte, vmscan
                         * will take care of the rest.
                         * A future reference will then fault in a new zero
                         * page. When userfaultfd is active, we must not drop
                         * this page though, as its main user (postcopy
                         * migration) will not expect userfaults on already
                         * copied pages.
                         */
                        dec_mm_counter(mm, mm_counter(folio));
                } else if (folio_test_anon(folio)) {
                        swp_entry_t entry = page_swap_entry(subpage);
                        pte_t swp_pte;
                        /*
                         * Store the swap location in the pte.
                         * See handle_pte_fault() ...
                         */
                        if (unlikely(folio_test_swapbacked(folio) !=
                                        folio_test_swapcache(folio))) {
                                WARN_ON_ONCE(1);
                                goto walk_abort;
                        }

                        /* MADV_FREE page check */
                        if (!folio_test_swapbacked(folio)) {
                                int ref_count, map_count;

                                /*
                                 * Synchronize with gup_pte_range():
                                 * - clear PTE; barrier; read refcount
                                 * - inc refcount; barrier; read PTE
                                 */
                                smp_mb();

                                ref_count = folio_ref_count(folio);
                                map_count = folio_mapcount(folio);

                                /*
                                 * Order reads for page refcount and dirty flag
                                 * (see comments in __remove_mapping()).
                                 */
                                smp_rmb();

                                if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) {
                                        /*
                                         * redirtied either using the page table or a previously
                                         * obtained GUP reference.
                                         */
                                        set_ptes(mm, address, pvmw.pte, pteval, nr_pages);
                                        folio_set_swapbacked(folio);
                                        goto walk_abort;
                                } else if (ref_count != 1 + map_count) {
                                        /*
                                         * Additional reference. Could be a GUP reference or any
                                         * speculative reference. GUP users must mark the folio
                                         * dirty if there was a modification. This folio cannot be
                                         * reclaimed right now either way, so act just like nothing
                                         * happened.
                                         * We'll come back here later and detect if the folio was
                                         * dirtied when the additional reference is gone.
                                         */
                                        set_ptes(mm, address, pvmw.pte, pteval, nr_pages);
                                        goto walk_abort;
                                }
                                add_mm_counter(mm, MM_ANONPAGES, -nr_pages);
                                goto discard;
                        }

                        if (folio_dup_swap(folio, subpage) < 0) {
                                set_pte_at(mm, address, pvmw.pte, pteval);
                                goto walk_abort;
                        }

                        /*
                         * arch_unmap_one() is expected to be a NOP on
                         * architectures where we could have PFN swap PTEs,
                         * so we'll not check/care.
                         */
                        if (arch_unmap_one(mm, vma, address, pteval) < 0) {
                                folio_put_swap(folio, subpage);
                                set_pte_at(mm, address, pvmw.pte, pteval);
                                goto walk_abort;
                        }

                        /* See folio_try_share_anon_rmap(): clear PTE first. */
                        if (anon_exclusive &&
                            folio_try_share_anon_rmap_pte(folio, subpage)) {
                                folio_put_swap(folio, subpage);
                                set_pte_at(mm, address, pvmw.pte, pteval);
                                goto walk_abort;
                        }
                        if (list_empty(&mm->mmlist)) {
                                spin_lock(&mmlist_lock);
                                if (list_empty(&mm->mmlist))
                                        list_add(&mm->mmlist, &init_mm.mmlist);
                                spin_unlock(&mmlist_lock);
                        }
                        dec_mm_counter(mm, MM_ANONPAGES);
                        inc_mm_counter(mm, MM_SWAPENTS);
                        swp_pte = swp_entry_to_pte(entry);
                        if (anon_exclusive)
                                swp_pte = pte_swp_mkexclusive(swp_pte);
                        if (likely(pte_present(pteval))) {
                                if (pte_soft_dirty(pteval))
                                        swp_pte = pte_swp_mksoft_dirty(swp_pte);
                                if (pte_uffd_wp(pteval))
                                        swp_pte = pte_swp_mkuffd_wp(swp_pte);
                        } else {
                                if (pte_swp_soft_dirty(pteval))
                                        swp_pte = pte_swp_mksoft_dirty(swp_pte);
                                if (pte_swp_uffd_wp(pteval))
                                        swp_pte = pte_swp_mkuffd_wp(swp_pte);
                        }
                        set_pte_at(mm, address, pvmw.pte, swp_pte);
                } else {
                        /*
                         * This is a locked file-backed folio,
                         * so it cannot be removed from the page
                         * cache and replaced by a new folio before
                         * mmu_notifier_invalidate_range_end, so no
                         * concurrent thread might update its page table
                         * to point at a new folio while a device is
                         * still using this folio.
                         *
                         * See Documentation/mm/mmu_notifier.rst
                         */
                        add_mm_counter(mm, mm_counter_file(folio), -nr_pages);
                }
discard:
                if (unlikely(folio_test_hugetlb(folio))) {
                        hugetlb_remove_rmap(folio);
                } else {
                        folio_remove_rmap_ptes(folio, subpage, nr_pages, vma);
                }
                if (vma->vm_flags & VM_LOCKED)
                        mlock_drain_local();
                folio_put_refs(folio, nr_pages);

                /*
                 * If we are sure that we batched the entire folio and cleared
                 * all PTEs, we can just optimize and stop right here.
                 */
                if (nr_pages == folio_nr_pages(folio))
                        goto walk_done;
                continue;
walk_abort:
                ret = false;
walk_done:
                page_vma_mapped_walk_done(&pvmw);
                break;
        }

        mmu_notifier_invalidate_range_end(&range);

        return ret;
}

static bool invalid_migration_vma(struct vm_area_struct *vma, void *arg)
{
        return vma_is_temporary_stack(vma);
}

static int folio_not_mapped(struct folio *folio)
{
        return !folio_mapped(folio);
}

/**
 * try_to_unmap - Try to remove all page table mappings to a folio.
 * @folio: The folio to unmap.
 * @flags: action and flags
 *
 * Tries to remove all the page table entries which are mapping this
 * folio.  It is the caller's responsibility to check if the folio is
 * still mapped if needed (use TTU_SYNC to prevent accounting races).
 *
 * Context: Caller must hold the folio lock.
 */
void try_to_unmap(struct folio *folio, enum ttu_flags flags)
{
        struct rmap_walk_control rwc = {
                .rmap_one = try_to_unmap_one,
                .arg = (void *)flags,
                .done = folio_not_mapped,
                .anon_lock = folio_lock_anon_vma_read,
        };

        if (flags & TTU_RMAP_LOCKED)
                rmap_walk_locked(folio, &rwc);
        else
                rmap_walk(folio, &rwc);
}

/*
 * @arg: enum ttu_flags will be passed to this argument.
 *
 * If TTU_SPLIT_HUGE_PMD is specified any PMD mappings will be split into PTEs
 * containing migration entries.
 */
static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
                     unsigned long address, void *arg)
{
        struct mm_struct *mm = vma->vm_mm;
        DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0);
        bool anon_exclusive, writable, ret = true;
        pte_t pteval;
        struct page *subpage;
        struct mmu_notifier_range range;
        enum ttu_flags flags = (enum ttu_flags)(long)arg;
        unsigned long pfn;
        unsigned long hsz = 0;

        /*
         * When racing against e.g. zap_pte_range() on another cpu,
         * in between its ptep_get_and_clear_full() and folio_remove_rmap_*(),
         * try_to_migrate() may return before page_mapped() has become false,
         * if page table locking is skipped: use TTU_SYNC to wait for that.
         */
        if (flags & TTU_SYNC)
                pvmw.flags = PVMW_SYNC;

        /*
         * For THP, we have to assume the worse case ie pmd for invalidation.
         * For hugetlb, it could be much worse if we need to do pud
         * invalidation in the case of pmd sharing.
         *
         * Note that the page can not be free in this function as call of
         * try_to_unmap() must hold a reference on the page.
         */
        range.end = vma_address_end(&pvmw);
        mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma->vm_mm,
                                address, range.end);
        if (folio_test_hugetlb(folio)) {
                /*
                 * If sharing is possible, start and end will be adjusted
                 * accordingly.
                 */
                adjust_range_if_pmd_sharing_possible(vma, &range.start,
                                                     &range.end);

                /* We need the huge page size for set_huge_pte_at() */
                hsz = huge_page_size(hstate_vma(vma));
        }
        mmu_notifier_invalidate_range_start(&range);

        while (page_vma_mapped_walk(&pvmw)) {
                /* PMD-mapped THP migration entry */
                if (!pvmw.pte) {
                        __maybe_unused unsigned long pfn;
                        __maybe_unused pmd_t pmdval;

                        if (flags & TTU_SPLIT_HUGE_PMD) {
                                /*
                                 * split_huge_pmd_locked() might leave the
                                 * folio mapped through PTEs. Retry the walk
                                 * so we can detect this scenario and properly
                                 * abort the walk.
                                 */
                                split_huge_pmd_locked(vma, pvmw.address,
                                                      pvmw.pmd, true);
                                flags &= ~TTU_SPLIT_HUGE_PMD;
                                page_vma_mapped_walk_restart(&pvmw);
                                continue;
                        }
#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
                        pmdval = pmdp_get(pvmw.pmd);
                        if (likely(pmd_present(pmdval)))
                                pfn = pmd_pfn(pmdval);
                        else
                                pfn = softleaf_to_pfn(softleaf_from_pmd(pmdval));

                        subpage = folio_page(folio, pfn - folio_pfn(folio));

                        VM_BUG_ON_FOLIO(folio_test_hugetlb(folio) ||
                                        !folio_test_pmd_mappable(folio), folio);

                        if (set_pmd_migration_entry(&pvmw, subpage)) {
                                ret = false;
                                page_vma_mapped_walk_done(&pvmw);
                                break;
                        }
                        continue;
#endif
                }

                /* Unexpected PMD-mapped THP? */
                VM_BUG_ON_FOLIO(!pvmw.pte, folio);

                /*
                 * Handle PFN swap PTEs, such as device-exclusive ones, that
                 * actually map pages.
                 */
                pteval = ptep_get(pvmw.pte);
                if (likely(pte_present(pteval))) {
                        pfn = pte_pfn(pteval);
                } else {
                        const softleaf_t entry = softleaf_from_pte(pteval);

                        pfn = softleaf_to_pfn(entry);
                        VM_WARN_ON_FOLIO(folio_test_hugetlb(folio), folio);
                }

                subpage = folio_page(folio, pfn - folio_pfn(folio));
                address = pvmw.address;
                anon_exclusive = folio_test_anon(folio) &&
                                 PageAnonExclusive(subpage);

                if (folio_test_hugetlb(folio)) {
                        bool anon = folio_test_anon(folio);

                        /*
                         * huge_pmd_unshare may unmap an entire PMD page.
                         * There is no way of knowing exactly which PMDs may
                         * be cached for this mm, so we must flush them all.
                         * start/end were already adjusted above to cover this
                         * range.
                         */
                        flush_cache_range(vma, range.start, range.end);

                        /*
                         * To call huge_pmd_unshare, i_mmap_rwsem must be
                         * held in write mode.  Caller needs to explicitly
                         * do this outside rmap routines.
                         *
                         * We also must hold hugetlb vma_lock in write mode.
                         * Lock order dictates acquiring vma_lock BEFORE
                         * i_mmap_rwsem.  We can only try lock here and
                         * fail if unsuccessful.
                         */
                        if (!anon) {
                                struct mmu_gather tlb;

                                VM_BUG_ON(!(flags & TTU_RMAP_LOCKED));
                                if (!hugetlb_vma_trylock_write(vma)) {
                                        page_vma_mapped_walk_done(&pvmw);
                                        ret = false;
                                        break;
                                }

                                tlb_gather_mmu_vma(&tlb, vma);
                                if (huge_pmd_unshare(&tlb, vma, address, pvmw.pte)) {
                                        hugetlb_vma_unlock_write(vma);
                                        huge_pmd_unshare_flush(&tlb, vma);
                                        tlb_finish_mmu(&tlb);
                                        /*
                                         * The PMD table was unmapped,
                                         * consequently unmapping the folio.
                                         */
                                        page_vma_mapped_walk_done(&pvmw);
                                        break;
                                }
                                hugetlb_vma_unlock_write(vma);
                                tlb_finish_mmu(&tlb);
                        }
                        /* Nuke the hugetlb page table entry */
                        pteval = huge_ptep_clear_flush(vma, address, pvmw.pte);
                        if (pte_dirty(pteval))
                                folio_mark_dirty(folio);
                        writable = pte_write(pteval);
                } else if (likely(pte_present(pteval))) {
                        flush_cache_page(vma, address, pfn);
                        /* Nuke the page table entry. */
                        if (should_defer_flush(mm, flags)) {
                                /*
                                 * We clear the PTE but do not flush so potentially
                                 * a remote CPU could still be writing to the folio.
                                 * If the entry was previously clean then the
                                 * architecture must guarantee that a clear->dirty
                                 * transition on a cached TLB entry is written through
                                 * and traps if the PTE is unmapped.
                                 */
                                pteval = ptep_get_and_clear(mm, address, pvmw.pte);

                                set_tlb_ubc_flush_pending(mm, pteval, address, address + PAGE_SIZE);
                        } else {
                                pteval = ptep_clear_flush(vma, address, pvmw.pte);
                        }
                        if (pte_dirty(pteval))
                                folio_mark_dirty(folio);
                        writable = pte_write(pteval);
                } else {
                        const softleaf_t entry = softleaf_from_pte(pteval);

                        pte_clear(mm, address, pvmw.pte);

                        writable = softleaf_is_device_private_write(entry);
                }

                VM_WARN_ON_FOLIO(writable && folio_test_anon(folio) &&
                                !anon_exclusive, folio);

                /* Update high watermark before we lower rss */
                update_hiwater_rss(mm);

                if (PageHWPoison(subpage)) {
                        VM_WARN_ON_FOLIO(folio_is_device_private(folio), folio);

                        pteval = swp_entry_to_pte(make_hwpoison_entry(subpage));
                        if (folio_test_hugetlb(folio)) {
                                hugetlb_count_sub(folio_nr_pages(folio), mm);
                                set_huge_pte_at(mm, address, pvmw.pte, pteval,
                                                hsz);
                        } else {
                                dec_mm_counter(mm, mm_counter(folio));
                                set_pte_at(mm, address, pvmw.pte, pteval);
                        }
                } else if (likely(pte_present(pteval)) && pte_unused(pteval) &&
                           !userfaultfd_armed(vma)) {
                        /*
                         * The guest indicated that the page content is of no
                         * interest anymore. Simply discard the pte, vmscan
                         * will take care of the rest.
                         * A future reference will then fault in a new zero
                         * page. When userfaultfd is active, we must not drop
                         * this page though, as its main user (postcopy
                         * migration) will not expect userfaults on already
                         * copied pages.
                         */
                        dec_mm_counter(mm, mm_counter(folio));
                } else {
                        swp_entry_t entry;
                        pte_t swp_pte;

                        /*
                         * arch_unmap_one() is expected to be a NOP on
                         * architectures where we could have PFN swap PTEs,
                         * so we'll not check/care.
                         */
                        if (arch_unmap_one(mm, vma, address, pteval) < 0) {
                                if (folio_test_hugetlb(folio))
                                        set_huge_pte_at(mm, address, pvmw.pte,
                                                        pteval, hsz);
                                else
                                        set_pte_at(mm, address, pvmw.pte, pteval);
                                ret = false;
                                page_vma_mapped_walk_done(&pvmw);
                                break;
                        }

                        /* See folio_try_share_anon_rmap_pte(): clear PTE first. */
                        if (folio_test_hugetlb(folio)) {
                                if (anon_exclusive &&
                                    hugetlb_try_share_anon_rmap(folio)) {
                                        set_huge_pte_at(mm, address, pvmw.pte,
                                                        pteval, hsz);
                                        ret = false;
                                        page_vma_mapped_walk_done(&pvmw);
                                        break;
                                }
                        } else if (anon_exclusive &&
                                   folio_try_share_anon_rmap_pte(folio, subpage)) {
                                set_pte_at(mm, address, pvmw.pte, pteval);
                                ret = false;
                                page_vma_mapped_walk_done(&pvmw);
                                break;
                        }

                        /*
                         * Store the pfn of the page in a special migration
                         * pte. do_swap_page() will wait until the migration
                         * pte is removed and then restart fault handling.
                         */
                        if (writable)
                                entry = make_writable_migration_entry(
                                                        page_to_pfn(subpage));
                        else if (anon_exclusive)
                                entry = make_readable_exclusive_migration_entry(
                                                        page_to_pfn(subpage));
                        else
                                entry = make_readable_migration_entry(
                                                        page_to_pfn(subpage));
                        if (likely(pte_present(pteval))) {
                                if (pte_young(pteval))
                                        entry = make_migration_entry_young(entry);
                                if (pte_dirty(pteval))
                                        entry = make_migration_entry_dirty(entry);
                                swp_pte = swp_entry_to_pte(entry);
                                if (pte_soft_dirty(pteval))
                                        swp_pte = pte_swp_mksoft_dirty(swp_pte);
                                if (pte_uffd_wp(pteval))
                                        swp_pte = pte_swp_mkuffd_wp(swp_pte);
                        } else {
                                swp_pte = swp_entry_to_pte(entry);
                                if (pte_swp_soft_dirty(pteval))
                                        swp_pte = pte_swp_mksoft_dirty(swp_pte);
                                if (pte_swp_uffd_wp(pteval))
                                        swp_pte = pte_swp_mkuffd_wp(swp_pte);
                        }
                        if (folio_test_hugetlb(folio))
                                set_huge_pte_at(mm, address, pvmw.pte, swp_pte,
                                                hsz);
                        else
                                set_pte_at(mm, address, pvmw.pte, swp_pte);
                        trace_set_migration_pte(address, pte_val(swp_pte),
                                                folio_order(folio));
                        /*
                         * No need to invalidate here it will synchronize on
                         * against the special swap migration pte.
                         */
                }

                if (unlikely(folio_test_hugetlb(folio)))
                        hugetlb_remove_rmap(folio);
                else
                        folio_remove_rmap_pte(folio, subpage, vma);
                if (vma->vm_flags & VM_LOCKED)
                        mlock_drain_local();
                folio_put(folio);
        }

        mmu_notifier_invalidate_range_end(&range);

        return ret;
}

/**
 * try_to_migrate - try to replace all page table mappings with swap entries
 * @folio: the folio to replace page table entries for
 * @flags: action and flags
 *
 * Tries to remove all the page table entries which are mapping this folio and
 * replace them with special swap entries. Caller must hold the folio lock.
 */
void try_to_migrate(struct folio *folio, enum ttu_flags flags)
{
        struct rmap_walk_control rwc = {
                .rmap_one = try_to_migrate_one,
                .arg = (void *)flags,
                .done = folio_not_mapped,
                .anon_lock = folio_lock_anon_vma_read,
        };

        /*
         * Migration always ignores mlock and only supports TTU_RMAP_LOCKED and
         * TTU_SPLIT_HUGE_PMD, TTU_SYNC, and TTU_BATCH_FLUSH flags.
         */
        if (WARN_ON_ONCE(flags & ~(TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD |
                                        TTU_SYNC | TTU_BATCH_FLUSH)))
                return;

        if (folio_is_zone_device(folio) &&
            (!folio_is_device_private(folio) && !folio_is_device_coherent(folio)))
                return;

        /*
         * During exec, a temporary VMA is setup and later moved.
         * The VMA is moved under the anon_vma lock but not the
         * page tables leading to a race where migration cannot
         * find the migration ptes. Rather than increasing the
         * locking requirements of exec(), migration skips
         * temporary VMAs until after exec() completes.
         */
        if (!folio_test_ksm(folio) && folio_test_anon(folio))
                rwc.invalid_vma = invalid_migration_vma;

        if (flags & TTU_RMAP_LOCKED)
                rmap_walk_locked(folio, &rwc);
        else
                rmap_walk(folio, &rwc);
}

#ifdef CONFIG_DEVICE_PRIVATE
/**
 * make_device_exclusive() - Mark a page for exclusive use by a device
 * @mm: mm_struct of associated target process
 * @addr: the virtual address to mark for exclusive device access
 * @owner: passed to MMU_NOTIFY_EXCLUSIVE range notifier to allow filtering
 * @foliop: folio pointer will be stored here on success.
 *
 * This function looks up the page mapped at the given address, grabs a
 * folio reference, locks the folio and replaces the PTE with special
 * device-exclusive PFN swap entry, preventing access through the process
 * page tables. The function will return with the folio locked and referenced.
 *
 * On fault, the device-exclusive entries are replaced with the original PTE
 * under folio lock, after calling MMU notifiers.
 *
 * Only anonymous non-hugetlb folios are supported and the VMA must have
 * write permissions such that we can fault in the anonymous page writable
 * in order to mark it exclusive. The caller must hold the mmap_lock in read
 * mode.
 *
 * A driver using this to program access from a device must use a mmu notifier
 * critical section to hold a device specific lock during programming. Once
 * programming is complete it should drop the folio lock and reference after
 * which point CPU access to the page will revoke the exclusive access.
 *
 * Notes:
 *   #. This function always operates on individual PTEs mapping individual
 *      pages. PMD-sized THPs are first remapped to be mapped by PTEs before
 *      the conversion happens on a single PTE corresponding to @addr.
 *   #. While concurrent access through the process page tables is prevented,
 *      concurrent access through other page references (e.g., earlier GUP
 *      invocation) is not handled and not supported.
 *   #. device-exclusive entries are considered "clean" and "old" by core-mm.
 *      Device drivers must update the folio state when informed by MMU
 *      notifiers.
 *
 * Returns: pointer to mapped page on success, otherwise a negative error.
 */
struct page *make_device_exclusive(struct mm_struct *mm, unsigned long addr,
                void *owner, struct folio **foliop)
{
        struct mmu_notifier_range range;
        struct folio *folio, *fw_folio;
        struct vm_area_struct *vma;
        struct folio_walk fw;
        struct page *page;
        swp_entry_t entry;
        pte_t swp_pte;
        int ret;

        mmap_assert_locked(mm);
        addr = PAGE_ALIGN_DOWN(addr);

        /*
         * Fault in the page writable and try to lock it; note that if the
         * address would already be marked for exclusive use by a device,
         * the GUP call would undo that first by triggering a fault.
         *
         * If any other device would already map this page exclusively, the
         * fault will trigger a conversion to an ordinary
         * (non-device-exclusive) PTE and issue a MMU_NOTIFY_EXCLUSIVE.
         */
retry:
        page = get_user_page_vma_remote(mm, addr,
                                        FOLL_GET | FOLL_WRITE | FOLL_SPLIT_PMD,
                                        &vma);
        if (IS_ERR(page))
                return page;
        folio = page_folio(page);

        if (!folio_test_anon(folio) || folio_test_hugetlb(folio)) {
                folio_put(folio);
                return ERR_PTR(-EOPNOTSUPP);
        }

        ret = folio_lock_killable(folio);
        if (ret) {
                folio_put(folio);
                return ERR_PTR(ret);
        }

        /*
         * Inform secondary MMUs that we are going to convert this PTE to
         * device-exclusive, such that they unmap it now. Note that the
         * caller must filter this event out to prevent livelocks.
         */
        mmu_notifier_range_init_owner(&range, MMU_NOTIFY_EXCLUSIVE, 0,
                                      mm, addr, addr + PAGE_SIZE, owner);
        mmu_notifier_invalidate_range_start(&range);

        /*
         * Let's do a second walk and make sure we still find the same page
         * mapped writable. Note that any page of an anonymous folio can
         * only be mapped writable using exactly one PTE ("exclusive"), so
         * there cannot be other mappings.
         */
        fw_folio = folio_walk_start(&fw, vma, addr, 0);
        if (fw_folio != folio || fw.page != page ||
            fw.level != FW_LEVEL_PTE || !pte_write(fw.pte)) {
                if (fw_folio)
                        folio_walk_end(&fw, vma);
                mmu_notifier_invalidate_range_end(&range);
                folio_unlock(folio);
                folio_put(folio);
                goto retry;
        }

        /* Nuke the page table entry so we get the uptodate dirty bit. */
        flush_cache_page(vma, addr, page_to_pfn(page));
        fw.pte = ptep_clear_flush(vma, addr, fw.ptep);

        /* Set the dirty flag on the folio now the PTE is gone. */
        if (pte_dirty(fw.pte))
                folio_mark_dirty(folio);

        /*
         * Store the pfn of the page in a special device-exclusive PFN swap PTE.
         * do_swap_page() will trigger the conversion back while holding the
         * folio lock.
         */
        entry = make_device_exclusive_entry(page_to_pfn(page));
        swp_pte = swp_entry_to_pte(entry);
        if (pte_soft_dirty(fw.pte))
                swp_pte = pte_swp_mksoft_dirty(swp_pte);
        /* The pte is writable, uffd-wp does not apply. */
        set_pte_at(mm, addr, fw.ptep, swp_pte);

        folio_walk_end(&fw, vma);
        mmu_notifier_invalidate_range_end(&range);
        *foliop = folio;
        return page;
}
EXPORT_SYMBOL_GPL(make_device_exclusive);
#endif

void __put_anon_vma(struct anon_vma *anon_vma)
{
        struct anon_vma *root = anon_vma->root;

        anon_vma_free(anon_vma);
        if (root != anon_vma && atomic_dec_and_test(&root->refcount))
                anon_vma_free(root);
}

static struct anon_vma *rmap_walk_anon_lock(const struct folio *folio,
                                            struct rmap_walk_control *rwc)
{
        struct anon_vma *anon_vma;

        if (rwc->anon_lock)
                return rwc->anon_lock(folio, rwc);

        /*
         * Note: remove_migration_ptes() cannot use folio_lock_anon_vma_read()
         * because that depends on page_mapped(); but not all its usages
         * are holding mmap_lock. Users without mmap_lock are required to
         * take a reference count to prevent the anon_vma disappearing
         */
        anon_vma = folio_anon_vma(folio);
        if (!anon_vma)
                return NULL;

        if (anon_vma_trylock_read(anon_vma))
                goto out;

        if (rwc->try_lock) {
                anon_vma = NULL;
                rwc->contended = true;
                goto out;
        }

        anon_vma_lock_read(anon_vma);
out:
        return anon_vma;
}

/*
 * rmap_walk_anon - do something to anonymous page using the object-based
 * rmap method
 * @folio: the folio to be handled
 * @rwc: control variable according to each walk type
 * @locked: caller holds relevant rmap lock
 *
 * Find all the mappings of a folio using the mapping pointer and the vma
 * chains contained in the anon_vma struct it points to.
 */
static void rmap_walk_anon(struct folio *folio,
                struct rmap_walk_control *rwc, bool locked)
{
        struct anon_vma *anon_vma;
        pgoff_t pgoff_start, pgoff_end;
        struct anon_vma_chain *avc;

        /*
         * The folio lock ensures that folio->mapping can't be changed under us
         * to an anon_vma with different root.
         */
        VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio);

        if (locked) {
                anon_vma = folio_anon_vma(folio);
                /* anon_vma disappear under us? */
                VM_BUG_ON_FOLIO(!anon_vma, folio);
        } else {
                anon_vma = rmap_walk_anon_lock(folio, rwc);
        }
        if (!anon_vma)
                return;

        pgoff_start = folio_pgoff(folio);
        pgoff_end = pgoff_start + folio_nr_pages(folio) - 1;
        anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root,
                        pgoff_start, pgoff_end) {
                struct vm_area_struct *vma = avc->vma;
                unsigned long address = vma_address(vma, pgoff_start,
                                folio_nr_pages(folio));

                VM_BUG_ON_VMA(address == -EFAULT, vma);
                cond_resched();

                if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
                        continue;

                if (!rwc->rmap_one(folio, vma, address, rwc->arg))
                        break;
                if (rwc->done && rwc->done(folio))
                        break;
        }

        if (!locked)
                anon_vma_unlock_read(anon_vma);
}

/**
 * __rmap_walk_file() - Traverse the reverse mapping for a file-backed mapping
 * of a page mapped within a specified page cache object at a specified offset.
 *
 * @folio:              Either the folio whose mappings to traverse, or if NULL,
 *                      the callbacks specified in @rwc will be configured such
 *                      as to be able to look up mappings correctly.
 * @mapping:            The page cache object whose mapping VMAs we intend to
 *                      traverse. If @folio is non-NULL, this should be equal to
 *                      folio_mapping(folio).
 * @pgoff_start:        The offset within @mapping of the page which we are
 *                      looking up. If @folio is non-NULL, this should be equal
 *                      to folio_pgoff(folio).
 * @nr_pages:           The number of pages mapped by the mapping. If @folio is
 *                      non-NULL, this should be equal to folio_nr_pages(folio).
 * @rwc:                The reverse mapping walk control object describing how
 *                      the traversal should proceed.
 * @locked:             Is the @mapping already locked? If not, we acquire the
 *                      lock.
 */
static void __rmap_walk_file(struct folio *folio, struct address_space *mapping,
                             pgoff_t pgoff_start, unsigned long nr_pages,
                             struct rmap_walk_control *rwc, bool locked)
{
        pgoff_t pgoff_end = pgoff_start + nr_pages - 1;
        struct vm_area_struct *vma;

        VM_WARN_ON_FOLIO(folio && mapping != folio_mapping(folio), folio);
        VM_WARN_ON_FOLIO(folio && pgoff_start != folio_pgoff(folio), folio);
        VM_WARN_ON_FOLIO(folio && nr_pages != folio_nr_pages(folio), folio);

        if (!locked) {
                if (i_mmap_trylock_read(mapping))
                        goto lookup;

                if (rwc->try_lock) {
                        rwc->contended = true;
                        return;
                }

                i_mmap_lock_read(mapping);
        }
lookup:
        vma_interval_tree_foreach(vma, &mapping->i_mmap,
                        pgoff_start, pgoff_end) {
                unsigned long address = vma_address(vma, pgoff_start, nr_pages);

                VM_BUG_ON_VMA(address == -EFAULT, vma);
                cond_resched();

                if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
                        continue;

                if (!rwc->rmap_one(folio, vma, address, rwc->arg))
                        goto done;
                if (rwc->done && rwc->done(folio))
                        goto done;
        }
done:
        if (!locked)
                i_mmap_unlock_read(mapping);
}

/*
 * rmap_walk_file - do something to file page using the object-based rmap method
 * @folio: the folio to be handled
 * @rwc: control variable according to each walk type
 * @locked: caller holds relevant rmap lock
 *
 * Find all the mappings of a folio using the mapping pointer and the vma chains
 * contained in the address_space struct it points to.
 */
static void rmap_walk_file(struct folio *folio,
                struct rmap_walk_control *rwc, bool locked)
{
        /*
         * The folio lock not only makes sure that folio->mapping cannot
         * suddenly be NULLified by truncation, it makes sure that the structure
         * at mapping cannot be freed and reused yet, so we can safely take
         * mapping->i_mmap_rwsem.
         */
        VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);

        if (!folio->mapping)
                return;

        __rmap_walk_file(folio, folio->mapping, folio->index,
                         folio_nr_pages(folio), rwc, locked);
}

void rmap_walk(struct folio *folio, struct rmap_walk_control *rwc)
{
        if (unlikely(folio_test_ksm(folio)))
                rmap_walk_ksm(folio, rwc);
        else if (folio_test_anon(folio))
                rmap_walk_anon(folio, rwc, false);
        else
                rmap_walk_file(folio, rwc, false);
}

/* Like rmap_walk, but caller holds relevant rmap lock */
void rmap_walk_locked(struct folio *folio, struct rmap_walk_control *rwc)
{
        /* no ksm support for now */
        VM_BUG_ON_FOLIO(folio_test_ksm(folio), folio);
        if (folio_test_anon(folio))
                rmap_walk_anon(folio, rwc, true);
        else
                rmap_walk_file(folio, rwc, true);
}

#ifdef CONFIG_HUGETLB_PAGE
/*
 * The following two functions are for anonymous (private mapped) hugepages.
 * Unlike common anonymous pages, anonymous hugepages have no accounting code
 * and no lru code, because we handle hugepages differently from common pages.
 */
void hugetlb_add_anon_rmap(struct folio *folio, struct vm_area_struct *vma,
                unsigned long address, rmap_t flags)
{
        VM_WARN_ON_FOLIO(!folio_test_hugetlb(folio), folio);
        VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio);

        atomic_inc(&folio->_entire_mapcount);
        atomic_inc(&folio->_large_mapcount);
        if (flags & RMAP_EXCLUSIVE)
                SetPageAnonExclusive(&folio->page);
        VM_WARN_ON_FOLIO(folio_entire_mapcount(folio) > 1 &&
                         PageAnonExclusive(&folio->page), folio);
}

void hugetlb_add_new_anon_rmap(struct folio *folio,
                struct vm_area_struct *vma, unsigned long address)
{
        VM_WARN_ON_FOLIO(!folio_test_hugetlb(folio), folio);

        BUG_ON(address < vma->vm_start || address >= vma->vm_end);
        /* increment count (starts at -1) */
        atomic_set(&folio->_entire_mapcount, 0);
        atomic_set(&folio->_large_mapcount, 0);
        folio_clear_hugetlb_restore_reserve(folio);
        __folio_set_anon(folio, vma, address, true);
        SetPageAnonExclusive(&folio->page);
}
#endif /* CONFIG_HUGETLB_PAGE */