LXR linux/mm/page_vma

   1// SPDX-License-Identifier: GPL-2.0
   2#include <linux/mm.h>
   3#include <linux/rmap.h>
   4#include <linux/hugetlb.h>
   5#include <linux/swap.h>
   6#include <linux/swapops.h>
   7
   8#include "internal.h"
   9
  10static inline bool not_found(struct page_vma_mapped_walk *pvmw)
  11{
  12        page_vma_mapped_walk_done(pvmw);
  13        return false;
  14}
  15
  16static bool map_pte(struct page_vma_mapped_walk *pvmw)
  17{
  18        pvmw->pte = pte_offset_map(pvmw->pmd, pvmw->address);
  19        if (!(pvmw->flags & PVMW_SYNC)) {
  20                if (pvmw->flags & PVMW_MIGRATION) {
  21                        if (!is_swap_pte(*pvmw->pte))
  22                                return false;
  23                } else {
  24                        if (!pte_present(*pvmw->pte))
  25                                return false;
  26                }
  27        }
  28        pvmw->ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd);
  29        spin_lock(pvmw->ptl);
  30        return true;
  31}
  32
  33static inline bool pfn_in_hpage(struct page *hpage, unsigned long pfn)
  34{
  35        unsigned long hpage_pfn = page_to_pfn(hpage);
  36
  37        /* THP can be referenced by any subpage */
  38        return pfn >= hpage_pfn && pfn - hpage_pfn < hpage_nr_pages(hpage);
  39}
  40
  41/**
  42 * check_pte - check if @pvmw->page is mapped at the @pvmw->pte
  43 *
  44 * page_vma_mapped_walk() found a place where @pvmw->page is *potentially*
  45 * mapped. check_pte() has to validate this.
  46 *
  47 * @pvmw->pte may point to empty PTE, swap PTE or PTE pointing to arbitrary
  48 * page.
  49 *
  50 * If PVMW_MIGRATION flag is set, returns true if @pvmw->pte contains migration
  51 * entry that points to @pvmw->page or any subpage in case of THP.
  52 *
  53 * If PVMW_MIGRATION flag is not set, returns true if @pvmw->pte points to
  54 * @pvmw->page or any subpage in case of THP.
  55 *
  56 * Otherwise, return false.
  57 *
  58 */
  59static bool check_pte(struct page_vma_mapped_walk *pvmw)
  60{
  61        unsigned long pfn;
  62
  63        if (pvmw->flags & PVMW_MIGRATION) {
  64                swp_entry_t entry;
  65                if (!is_swap_pte(*pvmw->pte))
  66                        return false;
  67                entry = pte_to_swp_entry(*pvmw->pte);
  68
  69                if (!is_migration_entry(entry))
  70                        return false;
  71
  72                pfn = migration_entry_to_pfn(entry);
  73        } else if (is_swap_pte(*pvmw->pte)) {
  74                swp_entry_t entry;
  75
  76                /* Handle un-addressable ZONE_DEVICE memory */
  77                entry = pte_to_swp_entry(*pvmw->pte);
  78                if (!is_device_private_entry(entry))
  79                        return false;
  80
  81                pfn = device_private_entry_to_pfn(entry);
  82        } else {
  83                if (!pte_present(*pvmw->pte))
  84                        return false;
  85
  86                pfn = pte_pfn(*pvmw->pte);
  87        }
  88
  89        return pfn_in_hpage(pvmw->page, pfn);
  90}
  91
  92/**
  93 * page_vma_mapped_walk - check if @pvmw->page is mapped in @pvmw->vma at
  94 * @pvmw->address
  95 * @pvmw: pointer to struct page_vma_mapped_walk. page, vma, address and flags
  96 * must be set. pmd, pte and ptl must be NULL.
  97 *
  98 * Returns true if the page is mapped in the vma. @pvmw->pmd and @pvmw->pte point
  99 * to relevant page table entries. @pvmw->ptl is locked. @pvmw->address is
 100 * adjusted if needed (for PTE-mapped THPs).
 101 *
 102 * If @pvmw->pmd is set but @pvmw->pte is not, you have found PMD-mapped page
 103 * (usually THP). For PTE-mapped THP, you should run page_vma_mapped_walk() in
 104 * a loop to find all PTEs that map the THP.
 105 *
 106 * For HugeTLB pages, @pvmw->pte is set to the relevant page table entry
 107 * regardless of which page table level the page is mapped at. @pvmw->pmd is
 108 * NULL.
 109 *
 110 * Retruns false if there are no more page table entries for the page in
 111 * the vma. @pvmw->ptl is unlocked and @pvmw->pte is unmapped.
 112 *
 113 * If you need to stop the walk before page_vma_mapped_walk() returned false,
 114 * use page_vma_mapped_walk_done(). It will do the housekeeping.
 115 */
 116bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 117{
 118        struct mm_struct *mm = pvmw->vma->vm_mm;
 119        struct page *page = pvmw->page;
 120        pgd_t *pgd;
 121        p4d_t *p4d;
 122        pud_t *pud;
 123        pmd_t pmde;
 124
 125        /* The only possible pmd mapping has been handled on last iteration */
 126        if (pvmw->pmd && !pvmw->pte)
 127                return not_found(pvmw);
 128
 129        if (pvmw->pte)
 130                goto next_pte;
 131
 132        if (unlikely(PageHuge(pvmw->page))) {
 133                /* when pud is not present, pte will be NULL */
 134                pvmw->pte = huge_pte_offset(mm, pvmw->address,
 135                                            PAGE_SIZE << compound_order(page));
 136                if (!pvmw->pte)
 137                        return false;
 138
 139                pvmw->ptl = huge_pte_lockptr(page_hstate(page), mm, pvmw->pte);
 140                spin_lock(pvmw->ptl);
 141                if (!check_pte(pvmw))
 142                        return not_found(pvmw);
 143                return true;
 144        }
 145restart:
 146        pgd = pgd_offset(mm, pvmw->address);
 147        if (!pgd_present(*pgd))
 148                return false;
 149        p4d = p4d_offset(pgd, pvmw->address);
 150        if (!p4d_present(*p4d))
 151                return false;
 152        pud = pud_offset(p4d, pvmw->address);
 153        if (!pud_present(*pud))
 154                return false;
 155        pvmw->pmd = pmd_offset(pud, pvmw->address);
 156        /*
 157         * Make sure the pmd value isn't cached in a register by the
 158         * compiler and used as a stale value after we've observed a
 159         * subsequent update.
 160         */
 161        pmde = READ_ONCE(*pvmw->pmd);
 162        if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde)) {
 163                pvmw->ptl = pmd_lock(mm, pvmw->pmd);
 164                if (likely(pmd_trans_huge(*pvmw->pmd))) {
 165                        if (pvmw->flags & PVMW_MIGRATION)
 166                                return not_found(pvmw);
 167                        if (pmd_page(*pvmw->pmd) != page)
 168                                return not_found(pvmw);
 169                        return true;
 170                } else if (!pmd_present(*pvmw->pmd)) {
 171                        if (thp_migration_supported()) {
 172                                if (!(pvmw->flags & PVMW_MIGRATION))
 173                                        return not_found(pvmw);
 174                                if (is_migration_entry(pmd_to_swp_entry(*pvmw->pmd))) {
 175                                        swp_entry_t entry = pmd_to_swp_entry(*pvmw->pmd);
 176
 177                                        if (migration_entry_to_page(entry) != page)
 178                                                return not_found(pvmw);
 179                                        return true;
 180                                }
 181                        }
 182                        return not_found(pvmw);
 183                } else {
 184                        /* THP pmd was split under us: handle on pte level */
 185                        spin_unlock(pvmw->ptl);
 186                        pvmw->ptl = NULL;
 187                }
 188        } else if (!pmd_present(pmde)) {
 189                return false;
 190        }
 191        if (!map_pte(pvmw))
 192                goto next_pte;
 193        while (1) {
 194                if (check_pte(pvmw))
 195                        return true;
 196next_pte:
 197                /* Seek to next pte only makes sense for THP */
 198                if (!PageTransHuge(pvmw->page) || PageHuge(pvmw->page))
 199                        return not_found(pvmw);
 200                do {
 201                        pvmw->address += PAGE_SIZE;
 202                        if (pvmw->address >= pvmw->vma->vm_end ||
 203                            pvmw->address >=
 204                                        __vma_address(pvmw->page, pvmw->vma) +
 205                                        hpage_nr_pages(pvmw->page) * PAGE_SIZE)
 206                                return not_found(pvmw);
 207                        /* Did we cross page table boundary? */
 208                        if (pvmw->address % PMD_SIZE == 0) {
 209                                pte_unmap(pvmw->pte);
 210                                if (pvmw->ptl) {
 211                                        spin_unlock(pvmw->ptl);
 212                                        pvmw->ptl = NULL;
 213                                }
 214                                goto restart;
 215                        } else {
 216                                pvmw->pte++;
 217                        }
 218                } while (pte_none(*pvmw->pte));
 219
 220                if (!pvmw->ptl) {
 221                        pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
 222                        spin_lock(pvmw->ptl);
 223                }
 224        }
 225}
 226
 227/**
 228 * page_mapped_in_vma - check whether a page is really mapped in a VMA
 229 * @page: the page to test
 230 * @vma: the VMA to test
 231 *
 232 * Returns 1 if the page is mapped into the page tables of the VMA, 0
 233 * if the page is not mapped into the page tables of this VMA.  Only
 234 * valid for normal file or anonymous VMAs.
 235 */
 236int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
 237{
 238        struct page_vma_mapped_walk pvmw = {
 239                .page = page,
 240                .vma = vma,
 241                .flags = PVMW_SYNC,
 242        };
 243        unsigned long start, end;
 244
 245        start = __vma_address(page, vma);
 246        end = start + PAGE_SIZE * (hpage_nr_pages(page) - 1);
 247
 248        if (unlikely(end < vma->vm_start || start >= vma->vm_end))
 249                return 0;
 250        pvmw.address = max(start, vma->vm_start);
 251        if (!page_vma_mapped_walk(&pvmw))
 252                return 0;
 253        page_vma_mapped_walk_done(&pvmw);
 254        return 1;
 255}
 256