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Linux/mm/pagewalk.c

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

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