mm/page_vma_mapped.c

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