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