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
  52                 if (!is_migration_entry(entry))
  53                         return false;
  54                 if (migration_entry_to_page(entry) - pvmw->page >=
  55                                 hpage_nr_pages(pvmw->page)) {
  56                         return false;
  57                 }
  58                 if (migration_entry_to_page(entry) < pvmw->page)
  59                         return false;
  60 #else
  61                 WARN_ON_ONCE(1);
  62 #endif
  63         } else {
  64                 if (is_swap_pte(*pvmw->pte)) {
  65                         swp_entry_t entry;
  66
  67                         entry = pte_to_swp_entry(*pvmw->pte);
  68                         if (is_device_private_entry(entry) &&
  69                             device_private_entry_to_page(entry) == pvmw->page)
  70                                 return true;
  71                 }
  72
  73                 if (!pte_present(*pvmw->pte))
  74                         return false;
  75
  76                 /* THP can be referenced by any subpage */
  77                 if (pte_page(*pvmw->pte) - pvmw->page >=
  78                                 hpage_nr_pages(pvmw->page)) {
  79                         return false;
  80                 }
  81                 if (pte_page(*pvmw->pte) < pvmw->page)
  82                         return false;
  83         }
  84
  85         return true;
  86 }
  87
  88 /**
  89  * page_vma_mapped_walk - check if @pvmw->page is mapped in @pvmw->vma at
  90  * @pvmw->address
  91  * @pvmw: pointer to struct page_vma_mapped_walk. page, vma, address and flags
  92  * must be set. pmd, pte and ptl must be NULL.
  93  *
  94  * Returns true if the page is mapped in the vma. @pvmw->pmd and @pvmw->pte point
  95  * to relevant page table entries. @pvmw->ptl is locked. @pvmw->address is
  96  * adjusted if needed (for PTE-mapped THPs).
  97  *
  98  * If @pvmw->pmd is set but @pvmw->pte is not, you have found PMD-mapped page
  99  * (usually THP). For PTE-mapped THP, you should run page_vma_mapped_walk() in
 100  * a loop to find all PTEs that map the THP.
 101  *
 102  * For HugeTLB pages, @pvmw->pte is set to the relevant page table entry
 103  * regardless of which page table level the page is mapped at. @pvmw->pmd is
 104  * NULL.
 105  *
 106  * Retruns false if there are no more page table entries for the page in
 107  * the vma. @pvmw->ptl is unlocked and @pvmw->pte is unmapped.
 108  *
 109  * If you need to stop the walk before page_vma_mapped_walk() returned false,
 110  * use page_vma_mapped_walk_done(). It will do the housekeeping.
 111  */
 112 bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 113 {
 114         struct mm_struct *mm = pvmw->vma->vm_mm;
 115         struct page *page = pvmw->page;
 116         pgd_t *pgd;
 117         p4d_t *p4d;
 118         pud_t *pud;
 119
 120         /* The only possible pmd mapping has been handled on last iteration */
 121         if (pvmw->pmd && !pvmw->pte)
 122                 return not_found(pvmw);
 123
 124         if (pvmw->pte)
 125                 goto next_pte;
 126
 127         if (unlikely(PageHuge(pvmw->page))) {
 128                 /* when pud is not present, pte will be NULL */
 129                 pvmw->pte = huge_pte_offset(mm, pvmw->address,
 130                                             PAGE_SIZE << compound_order(page));
 131                 if (!pvmw->pte)
 132                         return false;
 133
 134                 pvmw->ptl = huge_pte_lockptr(page_hstate(page), mm, pvmw->pte);
 135                 spin_lock(pvmw->ptl);
 136                 if (!check_pte(pvmw))
 137                         return not_found(pvmw);
 138                 return true;
 139         }
 140 restart:
 141         pgd = pgd_offset(mm, pvmw->address);
 142         if (!pgd_present(*pgd))
 143                 return false;
 144         p4d = p4d_offset(pgd, pvmw->address);
 145         if (!p4d_present(*p4d))
 146                 return false;
 147         pud = pud_offset(p4d, pvmw->address);
 148         if (!pud_present(*pud))
 149                 return false;
 150         pvmw->pmd = pmd_offset(pud, pvmw->address);
 151         if (pmd_trans_huge(*pvmw->pmd) || is_pmd_migration_entry(*pvmw->pmd)) {
 152                 pvmw->ptl = pmd_lock(mm, pvmw->pmd);
 153                 if (likely(pmd_trans_huge(*pvmw->pmd))) {
 154                         if (pvmw->flags & PVMW_MIGRATION)
 155                                 return not_found(pvmw);
 156                         if (pmd_page(*pvmw->pmd) != page)
 157                                 return not_found(pvmw);
 158                         return true;
 159                 } else if (!pmd_present(*pvmw->pmd)) {
 160                         if (thp_migration_supported()) {
 161                                 if (!(pvmw->flags & PVMW_MIGRATION))
 162                                         return not_found(pvmw);
 163                                 if (is_migration_entry(pmd_to_swp_entry(*pvmw->pmd))) {
 164                                         swp_entry_t entry = pmd_to_swp_entry(*pvmw->pmd);
 165
 166                                         if (migration_entry_to_page(entry) != page)
 167                                                 return not_found(pvmw);
 168                                         return true;
 169                                 }
 170                         } else
 171                                 WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");
 172                         return not_found(pvmw);
 173                 } else {
 174                         /* THP pmd was split under us: handle on pte level */
 175                         spin_unlock(pvmw->ptl);
 176                         pvmw->ptl = NULL;
 177                 }
 178         } else {
 179                 if (!check_pmd(pvmw))
 180                         return false;
 181         }
 182         if (!map_pte(pvmw))
 183                 goto next_pte;
 184         while (1) {
 185                 if (check_pte(pvmw))
 186                         return true;
 187 next_pte:
 188                 /* Seek to next pte only makes sense for THP */
 189                 if (!PageTransHuge(pvmw->page) || PageHuge(pvmw->page))
 190                         return not_found(pvmw);
 191                 do {
 192                         pvmw->address += PAGE_SIZE;
 193                         if (pvmw->address >= pvmw->vma->vm_end ||
 194                             pvmw->address >=
 195                                         __vma_address(pvmw->page, pvmw->vma) +
 196                                         hpage_nr_pages(pvmw->page) * PAGE_SIZE)
 197                                 return not_found(pvmw);
 198                         /* Did we cross page table boundary? */
 199                         if (pvmw->address % PMD_SIZE == 0) {
 200                                 pte_unmap(pvmw->pte);
 201                                 if (pvmw->ptl) {
 202                                         spin_unlock(pvmw->ptl);
 203                                         pvmw->ptl = NULL;
 204                                 }
 205                                 goto restart;
 206                         } else {
 207                                 pvmw->pte++;
 208                         }
 209                 } while (pte_none(*pvmw->pte));
 210
 211                 if (!pvmw->ptl) {
 212                         pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
 213                         spin_lock(pvmw->ptl);
 214                 }
 215         }
 216 }
 217
 218 /**
 219  * page_mapped_in_vma - check whether a page is really mapped in a VMA
 220  * @page: the page to test
 221  * @vma: the VMA to test
 222  *
 223  * Returns 1 if the page is mapped into the page tables of the VMA, 0
 224  * if the page is not mapped into the page tables of this VMA.  Only
 225  * valid for normal file or anonymous VMAs.
 226  */
 227 int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
 228 {
 229         struct page_vma_mapped_walk pvmw = {
 230                 .page = page,
 231                 .vma = vma,
 232                 .flags = PVMW_SYNC,
 233         };
 234         unsigned long start, end;
 235
 236         start = __vma_address(page, vma);
 237         end = start + PAGE_SIZE * (hpage_nr_pages(page) - 1);
 238
 239         if (unlikely(end < vma->vm_start || start >= vma->vm_end))
 240                 return 0;
 241         pvmw.address = max(start, vma->vm_start);
 242         if (!page_vma_mapped_walk(&pvmw))
 243                 return 0;
 244         page_vma_mapped_walk_done(&pvmw);
 245         return 1;
 246 }