// SPDX-License-Identifier: GPL-2.0
#include <linux/mm.h>
#include <linux/rmap.h>
#include <linux/hugetlb.h>
#include <linux/swap.h>
#include <linux/leafops.h>

#include "internal.h"

static inline bool not_found(struct page_vma_mapped_walk *pvmw)
{
        page_vma_mapped_walk_done(pvmw);
        return false;
}

static bool map_pte(struct page_vma_mapped_walk *pvmw, pmd_t *pmdvalp,
                    spinlock_t **ptlp)
{
        bool is_migration;
        pte_t ptent;

        if (pvmw->flags & PVMW_SYNC) {
                /* Use the stricter lookup */
                pvmw->pte = pte_offset_map_lock(pvmw->vma->vm_mm, pvmw->pmd,
                                                pvmw->address, &pvmw->ptl);
                *ptlp = pvmw->ptl;
                return !!pvmw->pte;
        }

        is_migration = pvmw->flags & PVMW_MIGRATION;
again:
        /*
         * It is important to return the ptl corresponding to pte,
         * in case *pvmw->pmd changes underneath us; so we need to
         * return it even when choosing not to lock, in case caller
         * proceeds to loop over next ptes, and finds a match later.
         * Though, in most cases, page lock already protects this.
         */
        pvmw->pte = pte_offset_map_rw_nolock(pvmw->vma->vm_mm, pvmw->pmd,
                                             pvmw->address, pmdvalp, ptlp);
        if (!pvmw->pte)
                return false;

        ptent = ptep_get(pvmw->pte);

        if (pte_none(ptent)) {
                return false;
        } else if (pte_present(ptent)) {
                if (is_migration)
                        return false;
        } else if (!is_migration) {
                softleaf_t entry;

                /*
                 * Handle un-addressable ZONE_DEVICE memory.
                 *
                 * We get here when we are trying to unmap a private
                 * device page from the process address space. Such
                 * page is not CPU accessible and thus is mapped as
                 * a special swap entry, nonetheless it still does
                 * count as a valid regular mapping for the page
                 * (and is accounted as such in page maps count).
                 *
                 * So handle this special case as if it was a normal
                 * page mapping ie lock CPU page table and return true.
                 *
                 * For more details on device private memory see HMM
                 * (include/linux/hmm.h or mm/hmm.c).
                 */
                entry = softleaf_from_pte(ptent);
                if (!softleaf_is_device_private(entry) &&
                    !softleaf_is_device_exclusive(entry))
                        return false;
        }
        spin_lock(*ptlp);
        if (unlikely(!pmd_same(*pmdvalp, pmdp_get_lockless(pvmw->pmd)))) {
                pte_unmap_unlock(pvmw->pte, *ptlp);
                goto again;
        }
        pvmw->ptl = *ptlp;

        return true;
}

/**
 * check_pte - check if [pvmw->pfn, @pvmw->pfn + @pvmw->nr_pages) is
 * mapped at the @pvmw->pte
 * @pvmw: page_vma_mapped_walk struct, includes a pair pte and pfn range
 * for checking
 * @pte_nr: the number of small pages described by @pvmw->pte.
 *
 * page_vma_mapped_walk() found a place where pfn range is *potentially*
 * mapped. check_pte() has to validate this.
 *
 * pvmw->pte may point to empty PTE, swap PTE or PTE pointing to
 * arbitrary page.
 *
 * If PVMW_MIGRATION flag is set, returns true if @pvmw->pte contains migration
 * entry that points to [pvmw->pfn, @pvmw->pfn + @pvmw->nr_pages)
 *
 * If PVMW_MIGRATION flag is not set, returns true if pvmw->pte points to
 * [pvmw->pfn, @pvmw->pfn + @pvmw->nr_pages)
 *
 * Otherwise, return false.
 *
 */
static bool check_pte(struct page_vma_mapped_walk *pvmw, unsigned long pte_nr)
{
        unsigned long pfn;
        pte_t ptent = ptep_get(pvmw->pte);

        if (pvmw->flags & PVMW_MIGRATION) {
                const softleaf_t entry = softleaf_from_pte(ptent);

                if (!softleaf_is_migration(entry))
                        return false;

                pfn = softleaf_to_pfn(entry);
        } else if (pte_present(ptent)) {
                pfn = pte_pfn(ptent);
        } else {
                const softleaf_t entry = softleaf_from_pte(ptent);

                /* Handle un-addressable ZONE_DEVICE memory */
                if (!softleaf_is_device_private(entry) &&
                    !softleaf_is_device_exclusive(entry))
                        return false;

                pfn = softleaf_to_pfn(entry);
        }

        if ((pfn + pte_nr - 1) < pvmw->pfn)
                return false;
        if (pfn > (pvmw->pfn + pvmw->nr_pages - 1))
                return false;
        return true;
}

/* Returns true if the two ranges overlap.  Careful to not overflow. */
static bool check_pmd(unsigned long pfn, struct page_vma_mapped_walk *pvmw)
{
        if ((pfn + HPAGE_PMD_NR - 1) < pvmw->pfn)
                return false;
        if (pfn > pvmw->pfn + pvmw->nr_pages - 1)
                return false;
        return true;
}

static void step_forward(struct page_vma_mapped_walk *pvmw, unsigned long size)
{
        pvmw->address = (pvmw->address + size) & ~(size - 1);
        if (!pvmw->address)
                pvmw->address = ULONG_MAX;
}

/**
 * page_vma_mapped_walk - check if @pvmw->pfn is mapped in @pvmw->vma at
 * @pvmw->address
 * @pvmw: pointer to struct page_vma_mapped_walk. page, vma, address and flags
 * must be set. pmd, pte and ptl must be NULL.
 *
 * Returns true if the page is mapped in the vma. @pvmw->pmd and @pvmw->pte point
 * to relevant page table entries. @pvmw->ptl is locked. @pvmw->address is
 * adjusted if needed (for PTE-mapped THPs).
 *
 * If @pvmw->pmd is set but @pvmw->pte is not, you have found PMD-mapped page
 * (usually THP). For PTE-mapped THP, you should run page_vma_mapped_walk() in
 * a loop to find all PTEs that map the THP.
 *
 * For HugeTLB pages, @pvmw->pte is set to the relevant page table entry
 * regardless of which page table level the page is mapped at. @pvmw->pmd is
 * NULL.
 *
 * Returns false if there are no more page table entries for the page in
 * the vma. @pvmw->ptl is unlocked and @pvmw->pte is unmapped.
 *
 * If you need to stop the walk before page_vma_mapped_walk() returned false,
 * use page_vma_mapped_walk_done(). It will do the housekeeping.
 */
bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
{
        struct vm_area_struct *vma = pvmw->vma;
        struct mm_struct *mm = vma->vm_mm;
        unsigned long end;
        spinlock_t *ptl;
        pgd_t *pgd;
        p4d_t *p4d;
        pud_t *pud;
        pmd_t pmde;

        /* The only possible pmd mapping has been handled on last iteration */
        if (pvmw->pmd && !pvmw->pte)
                return not_found(pvmw);

        if (unlikely(is_vm_hugetlb_page(vma))) {
                struct hstate *hstate = hstate_vma(vma);
                unsigned long size = huge_page_size(hstate);
                /* The only possible mapping was handled on last iteration */
                if (pvmw->pte)
                        return not_found(pvmw);
                /*
                 * All callers that get here will already hold the
                 * i_mmap_rwsem.  Therefore, no additional locks need to be
                 * taken before calling hugetlb_walk().
                 */
                pvmw->pte = hugetlb_walk(vma, pvmw->address, size);
                if (!pvmw->pte)
                        return false;

                pvmw->ptl = huge_pte_lock(hstate, mm, pvmw->pte);
                if (!check_pte(pvmw, pages_per_huge_page(hstate)))
                        return not_found(pvmw);
                return true;
        }

        end = vma_address_end(pvmw);
        if (pvmw->pte)
                goto next_pte;
restart:
        do {
                pgd = pgd_offset(mm, pvmw->address);
                if (!pgd_present(*pgd)) {
                        step_forward(pvmw, PGDIR_SIZE);
                        continue;
                }
                p4d = p4d_offset(pgd, pvmw->address);
                if (!p4d_present(*p4d)) {
                        step_forward(pvmw, P4D_SIZE);
                        continue;
                }
                pud = pud_offset(p4d, pvmw->address);
                if (!pud_present(*pud)) {
                        step_forward(pvmw, PUD_SIZE);
                        continue;
                }

                pvmw->pmd = pmd_offset(pud, pvmw->address);
                /*
                 * Make sure the pmd value isn't cached in a register by the
                 * compiler and used as a stale value after we've observed a
                 * subsequent update.
                 */
                pmde = pmdp_get_lockless(pvmw->pmd);

                if (pmd_trans_huge(pmde) || pmd_is_migration_entry(pmde)) {
                        pvmw->ptl = pmd_lock(mm, pvmw->pmd);
                        pmde = *pvmw->pmd;
                        if (!pmd_present(pmde)) {
                                softleaf_t entry;

                                if (!thp_migration_supported() ||
                                    !(pvmw->flags & PVMW_MIGRATION))
                                        return not_found(pvmw);
                                entry = softleaf_from_pmd(pmde);

                                if (!softleaf_is_migration(entry) ||
                                    !check_pmd(softleaf_to_pfn(entry), pvmw))
                                        return not_found(pvmw);
                                return true;
                        }
                        if (likely(pmd_trans_huge(pmde))) {
                                if (pvmw->flags & PVMW_MIGRATION)
                                        return not_found(pvmw);
                                if (!check_pmd(pmd_pfn(pmde), pvmw))
                                        return not_found(pvmw);
                                return true;
                        }
                        /* THP pmd was split under us: handle on pte level */
                        spin_unlock(pvmw->ptl);
                        pvmw->ptl = NULL;
                } else if (!pmd_present(pmde)) {
                        /*
                         * If PVMW_SYNC, take and drop THP pmd lock so that we
                         * cannot return prematurely, while zap_huge_pmd() has
                         * cleared *pmd but not decremented compound_mapcount().
                         */
                        const softleaf_t entry = softleaf_from_pmd(pmde);

                        if (softleaf_is_device_private(entry)) {
                                pvmw->ptl = pmd_lock(mm, pvmw->pmd);
                                return true;
                        }

                        if ((pvmw->flags & PVMW_SYNC) &&
                            thp_vma_suitable_order(vma, pvmw->address,
                                                   PMD_ORDER) &&
                            (pvmw->nr_pages >= HPAGE_PMD_NR)) {
                                spinlock_t *ptl = pmd_lock(mm, pvmw->pmd);

                                spin_unlock(ptl);
                        }
                        step_forward(pvmw, PMD_SIZE);
                        continue;
                }
                if (!map_pte(pvmw, &pmde, &ptl)) {
                        if (!pvmw->pte)
                                goto restart;
                        goto next_pte;
                }
this_pte:
                if (check_pte(pvmw, 1))
                        return true;
next_pte:
                do {
                        pvmw->address += PAGE_SIZE;
                        if (pvmw->address >= end)
                                return not_found(pvmw);
                        /* Did we cross page table boundary? */
                        if ((pvmw->address & (PMD_SIZE - PAGE_SIZE)) == 0) {
                                if (pvmw->ptl) {
                                        spin_unlock(pvmw->ptl);
                                        pvmw->ptl = NULL;
                                }
                                pte_unmap(pvmw->pte);
                                pvmw->pte = NULL;
                                pvmw->flags |= PVMW_PGTABLE_CROSSED;
                                goto restart;
                        }
                        pvmw->pte++;
                } while (pte_none(ptep_get(pvmw->pte)));

                if (!pvmw->ptl) {
                        spin_lock(ptl);
                        if (unlikely(!pmd_same(pmde, pmdp_get_lockless(pvmw->pmd)))) {
                                pte_unmap_unlock(pvmw->pte, ptl);
                                pvmw->pte = NULL;
                                goto restart;
                        }
                        pvmw->ptl = ptl;
                }
                goto this_pte;
        } while (pvmw->address < end);

        return false;
}

#ifdef CONFIG_MEMORY_FAILURE
/**
 * page_mapped_in_vma - check whether a page is really mapped in a VMA
 * @page: the page to test
 * @vma: the VMA to test
 *
 * Return: The address the page is mapped at if the page is in the range
 * covered by the VMA and present in the page table.  If the page is
 * outside the VMA or not present, returns -EFAULT.
 * Only valid for normal file or anonymous VMAs.
 */
unsigned long page_mapped_in_vma(const struct page *page,
                struct vm_area_struct *vma)
{
        const struct folio *folio = page_folio(page);
        struct page_vma_mapped_walk pvmw = {
                .pfn = page_to_pfn(page),
                .nr_pages = 1,
                .vma = vma,
                .flags = PVMW_SYNC,
        };

        pvmw.address = vma_address(vma, page_pgoff(folio, page), 1);
        if (pvmw.address == -EFAULT)
                goto out;
        if (!page_vma_mapped_walk(&pvmw))
                return -EFAULT;
        page_vma_mapped_walk_done(&pvmw);
out:
        return pvmw.address;
}
#endif