mm/page_vma_mapped.c

   1 #include <linux/mm.h>
   2 #include <linux/rmap.h>
   3 #include <linux/hugetlb.h>
   4 #include <linux/swap.h>
   5 #include <linux/swapops.h>
   6
   7 #include "internal.h"
   8
   9 static inline bool check_pmd(struct page_vma_mapped_walk *pvmw)
  10 {
  11         pmd_t pmde;
  12         /*
  13          * Make sure we don't re-load pmd between present and !trans_huge check.
  14          * We need a consistent view.
  15          */
  16         pmde = READ_ONCE(*pvmw->pmd);
  17         return pmd_present(pmde) && !pmd_trans_huge(pmde);
  18 }
  19
  20 static inline bool not_found(struct page_vma_mapped_walk *pvmw)
  21 {
  22         page_vma_mapped_walk_done(pvmw);
  23         return false;
  24 }
  25
  26 static bool map_pte(struct page_vma_mapped_walk *pvmw)
  27 {
  28         pvmw->pte = pte_offset_map(pvmw->pmd, pvmw->address);
  29         if (!(pvmw->flags & PVMW_SYNC)) {
  30                 if (pvmw->flags & PVMW_MIGRATION) {
  31                         if (!is_swap_pte(*pvmw->pte))
  32                                 return false;
  33                 } else {
  34                         if (!pte_present(*pvmw->pte))
  35                                 return false;
  36                 }
  37         }
  38         pvmw->ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd);
  39         spin_lock(pvmw->ptl);
  40         return true;
  41 }
  42
  43 static bool check_pte(struct page_vma_mapped_walk *pvmw)
  44 {
  45         if (pvmw->flags & PVMW_MIGRATION) {
  46 #ifdef CONFIG_MIGRATION
  47                 swp_entry_t entry;
  48                 if (!is_swap_pte(*pvmw->pte))
  49                         return false;
  50                 entry = pte_to_swp_entry(*pvmw->pte);
  51                 if (!is_migration_entry(entry))
  52                         return false;
  53                 if (migration_entry_to_page(entry) - pvmw->page >=
  54                                 hpage_nr_pages(pvmw->page)) {
  55                         return false;
  56                 }
  57                 if (migration_entry_to_page(entry) < pvmw->page)
  58                         return false;
  59 #else
  60                 WARN_ON_ONCE(1);
  61 #endif
  62         } else {
  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
 110         /* The only possible pmd mapping has been handled on last iteration */
 111         if (pvmw->pmd && !pvmw->pte)
 112                 return not_found(pvmw);
 113
 114         if (pvmw->pte)
 115                 goto next_pte;
 116
 117         if (unlikely(PageHuge(pvmw->page))) {
 118                 /* when pud is not present, pte will be NULL */
 119                 pvmw->pte = huge_pte_offset(mm, pvmw->address,
 120                                             PAGE_SIZE << compound_order(page));
 121                 if (!pvmw->pte)
 122                         return false;
 123
 124                 pvmw->ptl = huge_pte_lockptr(page_hstate(page), mm, pvmw->pte);
 125                 spin_lock(pvmw->ptl);
 126                 if (!check_pte(pvmw))
 127                         return not_found(pvmw);
 128                 return true;
 129         }
 130 restart:
 131         pgd = pgd_offset(mm, pvmw->address);
 132         if (!pgd_present(*pgd))
 133                 return false;
 134         p4d = p4d_offset(pgd, pvmw->address);
 135         if (!p4d_present(*p4d))
 136                 return false;
 137         pud = pud_offset(p4d, pvmw->address);
 138         if (!pud_present(*pud))
 139                 return false;
 140         pvmw->pmd = pmd_offset(pud, pvmw->address);
 141         if (pmd_trans_huge(*pvmw->pmd)) {
 142                 pvmw->ptl = pmd_lock(mm, pvmw->pmd);
 143                 if (!pmd_present(*pvmw->pmd))
 144                         return not_found(pvmw);
 145                 if (likely(pmd_trans_huge(*pvmw->pmd))) {
 146                         if (pvmw->flags & PVMW_MIGRATION)
 147                                 return not_found(pvmw);
 148                         if (pmd_page(*pvmw->pmd) != page)
 149                                 return not_found(pvmw);
 150                         return true;
 151                 } else {
 152                         /* THP pmd was split under us: handle on pte level */
 153                         spin_unlock(pvmw->ptl);
 154                         pvmw->ptl = NULL;
 155                 }
 156         } else {
 157                 if (!check_pmd(pvmw))
 158                         return false;
 159         }
 160         if (!map_pte(pvmw))
 161                 goto next_pte;
 162         while (1) {
 163                 if (check_pte(pvmw))
 164                         return true;
 165 next_pte:
 166                 /* Seek to next pte only makes sense for THP */
 167                 if (!PageTransHuge(pvmw->page) || PageHuge(pvmw->page))
 168                         return not_found(pvmw);
 169                 do {
 170                         pvmw->address += PAGE_SIZE;
 171                         if (pvmw->address >= pvmw->vma->vm_end ||
 172                             pvmw->address >=
 173                                         __vma_address(pvmw->page, pvmw->vma) +
 174                                         hpage_nr_pages(pvmw->page) * PAGE_SIZE)
 175                                 return not_found(pvmw);
 176                         /* Did we cross page table boundary? */
 177                         if (pvmw->address % PMD_SIZE == 0) {
 178                                 pte_unmap(pvmw->pte);
 179                                 if (pvmw->ptl) {
 180                                         spin_unlock(pvmw->ptl);
 181                                         pvmw->ptl = NULL;
 182                                 }
 183                                 goto restart;
 184                         } else {
 185                                 pvmw->pte++;
 186                         }
 187                 } while (pte_none(*pvmw->pte));
 188
 189                 if (!pvmw->ptl) {
 190                         pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
 191                         spin_lock(pvmw->ptl);
 192                 }
 193         }
 194 }
 195
 196 /**
 197  * page_mapped_in_vma - check whether a page is really mapped in a VMA
 198  * @page: the page to test
 199  * @vma: the VMA to test
 200  *
 201  * Returns 1 if the page is mapped into the page tables of the VMA, 0
 202  * if the page is not mapped into the page tables of this VMA.  Only
 203  * valid for normal file or anonymous VMAs.
 204  */
 205 int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
 206 {
 207         struct page_vma_mapped_walk pvmw = {
 208                 .page = page,
 209                 .vma = vma,
 210                 .flags = PVMW_SYNC,
 211         };
 212         unsigned long start, end;
 213
 214         start = __vma_address(page, vma);
 215         end = start + PAGE_SIZE * (hpage_nr_pages(page) - 1);
 216
 217         if (unlikely(end < vma->vm_start || start >= vma->vm_end))
 218                 return 0;
 219         pvmw.address = max(start, vma->vm_start);
 220         if (!page_vma_mapped_walk(&pvmw))
 221                 return 0;
 222         page_vma_mapped_walk_done(&pvmw);
 223         return 1;
 224 }