mm/pagewalk.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/mm.h>
   3 #include <linux/highmem.h>
   4 #include <linux/sched.h>
   5 #include <linux/hugetlb.h>
   6
   7 static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
   8                           struct mm_walk *walk)
   9 {
  10         pte_t *pte;
  11         int err = 0;
  12
  13         pte = pte_offset_map(pmd, addr);
  14         for (;;) {
  15                 err = walk->pte_entry(pte, addr, addr + PAGE_SIZE, walk);
  16                 if (err)
  17                        break;
  18                 addr += PAGE_SIZE;
  19                 if (addr == end)
  20                         break;
  21                 pte++;
  22         }
  23
  24         pte_unmap(pte);
  25         return err;
  26 }
  27
  28 static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
  29                           struct mm_walk *walk)
  30 {
  31         pmd_t *pmd;
  32         unsigned long next;
  33         int err = 0;
  34
  35         pmd = pmd_offset(pud, addr);
  36         do {
  37 again:
  38                 next = pmd_addr_end(addr, end);
  39                 if (pmd_none(*pmd) || !walk->vma) {
  40                         if (walk->pte_hole)
  41                                 err = walk->pte_hole(addr, next, walk);
  42                         if (err)
  43                                 break;
  44                         continue;
  45                 }
  46                 /*
  47                  * This implies that each ->pmd_entry() handler
  48                  * needs to know about pmd_trans_huge() pmds
  49                  */
  50                 if (walk->pmd_entry)
  51                         err = walk->pmd_entry(pmd, addr, next, walk);
  52                 if (err)
  53                         break;
  54
  55                 /*
  56                  * Check this here so we only break down trans_huge
  57                  * pages when we _need_ to
  58                  */
  59                 if (!walk->pte_entry)
  60                         continue;
  61
  62                 split_huge_pmd(walk->vma, pmd, addr);
  63                 if (pmd_trans_unstable(pmd))
  64                         goto again;
  65                 err = walk_pte_range(pmd, addr, next, walk);
  66                 if (err)
  67                         break;
  68         } while (pmd++, addr = next, addr != end);
  69
  70         return err;
  71 }
  72
  73 static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
  74                           struct mm_walk *walk)
  75 {
  76         pud_t *pud;
  77         unsigned long next;
  78         int err = 0;
  79
  80         pud = pud_offset(p4d, addr);
  81         do {
  82  again:
  83                 next = pud_addr_end(addr, end);
  84                 if (pud_none(*pud) || !walk->vma) {
  85                         if (walk->pte_hole)
  86                                 err = walk->pte_hole(addr, next, walk);
  87                         if (err)
  88                                 break;
  89                         continue;
  90                 }
  91
  92                 if (walk->pud_entry) {
  93                         spinlock_t *ptl = pud_trans_huge_lock(pud, walk->vma);
  94
  95                         if (ptl) {
  96                                 err = walk->pud_entry(pud, addr, next, walk);
  97                                 spin_unlock(ptl);
  98                                 if (err)
  99                                         break;
 100                                 continue;
 101                         }
 102                 }
 103
 104                 split_huge_pud(walk->vma, pud, addr);
 105                 if (pud_none(*pud))
 106                         goto again;
 107
 108                 if (walk->pmd_entry || walk->pte_entry)
 109                         err = walk_pmd_range(pud, addr, next, walk);
 110                 if (err)
 111                         break;
 112         } while (pud++, addr = next, addr != end);
 113
 114         return err;
 115 }
 116
 117 static int walk_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,
 118                           struct mm_walk *walk)
 119 {
 120         p4d_t *p4d;
 121         unsigned long next;
 122         int err = 0;
 123
 124         p4d = p4d_offset(pgd, addr);
 125         do {
 126                 next = p4d_addr_end(addr, end);
 127                 if (p4d_none_or_clear_bad(p4d)) {
 128                         if (walk->pte_hole)
 129                                 err = walk->pte_hole(addr, next, walk);
 130                         if (err)
 131                                 break;
 132                         continue;
 133                 }
 134                 if (walk->pmd_entry || walk->pte_entry)
 135                         err = walk_pud_range(p4d, addr, next, walk);
 136                 if (err)
 137                         break;
 138         } while (p4d++, addr = next, addr != end);
 139
 140         return err;
 141 }
 142
 143 static int walk_pgd_range(unsigned long addr, unsigned long end,
 144                           struct mm_walk *walk)
 145 {
 146         pgd_t *pgd;
 147         unsigned long next;
 148         int err = 0;
 149
 150         pgd = pgd_offset(walk->mm, addr);
 151         do {
 152                 next = pgd_addr_end(addr, end);
 153                 if (pgd_none_or_clear_bad(pgd)) {
 154                         if (walk->pte_hole)
 155                                 err = walk->pte_hole(addr, next, walk);
 156                         if (err)
 157                                 break;
 158                         continue;
 159                 }
 160                 if (walk->pmd_entry || walk->pte_entry)
 161                         err = walk_p4d_range(pgd, addr, next, walk);
 162                 if (err)
 163                         break;
 164         } while (pgd++, addr = next, addr != end);
 165
 166         return err;
 167 }
 168
 169 #ifdef CONFIG_HUGETLB_PAGE
 170 static unsigned long hugetlb_entry_end(struct hstate *h, unsigned long addr,
 171                                        unsigned long end)
 172 {
 173         unsigned long boundary = (addr & huge_page_mask(h)) + huge_page_size(h);
 174         return boundary < end ? boundary : end;
 175 }
 176
 177 static int walk_hugetlb_range(unsigned long addr, unsigned long end,
 178                               struct mm_walk *walk)
 179 {
 180         struct vm_area_struct *vma = walk->vma;
 181         struct hstate *h = hstate_vma(vma);
 182         unsigned long next;
 183         unsigned long hmask = huge_page_mask(h);
 184         unsigned long sz = huge_page_size(h);
 185         pte_t *pte;
 186         int err = 0;
 187
 188         do {
 189                 next = hugetlb_entry_end(h, addr, end);
 190                 pte = huge_pte_offset(walk->mm, addr & hmask, sz);
 191
 192                 if (pte)
 193                         err = walk->hugetlb_entry(pte, hmask, addr, next, walk);
 194                 else if (walk->pte_hole)
 195                         err = walk->pte_hole(addr, next, walk);
 196
 197                 if (err)
 198                         break;
 199         } while (addr = next, addr != end);
 200
 201         return err;
 202 }
 203
 204 #else /* CONFIG_HUGETLB_PAGE */
 205 static int walk_hugetlb_range(unsigned long addr, unsigned long end,
 206                               struct mm_walk *walk)
 207 {
 208         return 0;
 209 }
 210
 211 #endif /* CONFIG_HUGETLB_PAGE */
 212
 213 /*
 214  * Decide whether we really walk over the current vma on [@start, @end)
 215  * or skip it via the returned value. Return 0 if we do walk over the
 216  * current vma, and return 1 if we skip the vma. Negative values means
 217  * error, where we abort the current walk.
 218  */
 219 static int walk_page_test(unsigned long start, unsigned long end,
 220                         struct mm_walk *walk)
 221 {
 222         struct vm_area_struct *vma = walk->vma;
 223
 224         if (walk->test_walk)
 225                 return walk->test_walk(start, end, walk);
 226
 227         /*
 228          * vma(VM_PFNMAP) doesn't have any valid struct pages behind VM_PFNMAP
 229          * range, so we don't walk over it as we do for normal vmas. However,
 230          * Some callers are interested in handling hole range and they don't
 231          * want to just ignore any single address range. Such users certainly
 232          * define their ->pte_hole() callbacks, so let's delegate them to handle
 233          * vma(VM_PFNMAP).
 234          */
 235         if (vma->vm_flags & VM_PFNMAP) {
 236                 int err = 1;
 237                 if (walk->pte_hole)
 238                         err = walk->pte_hole(start, end, walk);
 239                 return err ? err : 1;
 240         }
 241         return 0;
 242 }
 243
 244 static int __walk_page_range(unsigned long start, unsigned long end,
 245                         struct mm_walk *walk)
 246 {
 247         int err = 0;
 248         struct vm_area_struct *vma = walk->vma;
 249
 250         if (vma && is_vm_hugetlb_page(vma)) {
 251                 if (walk->hugetlb_entry)
 252                         err = walk_hugetlb_range(start, end, walk);
 253         } else
 254                 err = walk_pgd_range(start, end, walk);
 255
 256         return err;
 257 }
 258
 259 /**
 260  * walk_page_range - walk page table with caller specific callbacks
 261  *
 262  * Recursively walk the page table tree of the process represented by @walk->mm
 263  * within the virtual address range [@start, @end). During walking, we can do
 264  * some caller-specific works for each entry, by setting up pmd_entry(),
 265  * pte_entry(), and/or hugetlb_entry(). If you don't set up for some of these
 266  * callbacks, the associated entries/pages are just ignored.
 267  * The return values of these callbacks are commonly defined like below:
 268  *
 269  *  - 0  : succeeded to handle the current entry, and if you don't reach the
 270  *         end address yet, continue to walk.
 271  *  - >0 : succeeded to handle the current entry, and return to the caller
 272  *         with caller specific value.
 273  *  - <0 : failed to handle the current entry, and return to the caller
 274  *         with error code.
 275  *
 276  * Before starting to walk page table, some callers want to check whether
 277  * they really want to walk over the current vma, typically by checking
 278  * its vm_flags. walk_page_test() and @walk->test_walk() are used for this
 279  * purpose.
 280  *
 281  * struct mm_walk keeps current values of some common data like vma and pmd,
 282  * which are useful for the access from callbacks. If you want to pass some
 283  * caller-specific data to callbacks, @walk->private should be helpful.
 284  *
 285  * Locking:
 286  *   Callers of walk_page_range() and walk_page_vma() should hold
 287  *   @walk->mm->mmap_sem, because these function traverse vma list and/or
 288  *   access to vma's data.
 289  */
 290 int walk_page_range(unsigned long start, unsigned long end,
 291                     struct mm_walk *walk)
 292 {
 293         int err = 0;
 294         unsigned long next;
 295         struct vm_area_struct *vma;
 296
 297         if (start >= end)
 298                 return -EINVAL;
 299
 300         if (!walk->mm)
 301                 return -EINVAL;
 302
 303         VM_BUG_ON_MM(!rwsem_is_locked(&walk->mm->mmap_sem), walk->mm);
 304
 305         vma = find_vma(walk->mm, start);
 306         do {
 307                 if (!vma) { /* after the last vma */
 308                         walk->vma = NULL;
 309                         next = end;
 310                 } else if (start < vma->vm_start) { /* outside vma */
 311                         walk->vma = NULL;
 312                         next = min(end, vma->vm_start);
 313                 } else { /* inside vma */
 314                         walk->vma = vma;
 315                         next = min(end, vma->vm_end);
 316                         vma = vma->vm_next;
 317
 318                         err = walk_page_test(start, next, walk);
 319                         if (err > 0) {
 320                                 /*
 321                                  * positive return values are purely for
 322                                  * controlling the pagewalk, so should never
 323                                  * be passed to the callers.
 324                                  */
 325                                 err = 0;
 326                                 continue;
 327                         }
 328                         if (err < 0)
 329                                 break;
 330                 }
 331                 if (walk->vma || walk->pte_hole)
 332                         err = __walk_page_range(start, next, walk);
 333                 if (err)
 334                         break;
 335         } while (start = next, start < end);
 336         return err;
 337 }
 338
 339 int walk_page_vma(struct vm_area_struct *vma, struct mm_walk *walk)
 340 {
 341         int err;
 342
 343         if (!walk->mm)
 344                 return -EINVAL;
 345
 346         VM_BUG_ON(!rwsem_is_locked(&walk->mm->mmap_sem));
 347         VM_BUG_ON(!vma);
 348         walk->vma = vma;
 349         err = walk_page_test(vma->vm_start, vma->vm_end, walk);
 350         if (err > 0)
 351                 return 0;
 352         if (err < 0)
 353                 return err;
 354         return __walk_page_range(vma->vm_start, vma->vm_end, walk);
 355 }