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Linux/mm/pagewalk.c

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  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_page_pmd_mm(walk->mm, addr, pmd);
 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 
146                 if (pte)
147                         err = walk->hugetlb_entry(pte, hmask, addr, next, walk);
148                 else if (walk->pte_hole)
149                         err = walk->pte_hole(addr, next, walk);
150 
151                 if (err)
152                         break;
153         } while (addr = next, addr != end);
154 
155         return err;
156 }
157 
158 #else /* CONFIG_HUGETLB_PAGE */
159 static int walk_hugetlb_range(unsigned long addr, unsigned long end,
160                               struct mm_walk *walk)
161 {
162         return 0;
163 }
164 
165 #endif /* CONFIG_HUGETLB_PAGE */
166 
167 /*
168  * Decide whether we really walk over the current vma on [@start, @end)
169  * or skip it via the returned value. Return 0 if we do walk over the
170  * current vma, and return 1 if we skip the vma. Negative values means
171  * error, where we abort the current walk.
172  */
173 static int walk_page_test(unsigned long start, unsigned long end,
174                         struct mm_walk *walk)
175 {
176         struct vm_area_struct *vma = walk->vma;
177 
178         if (walk->test_walk)
179                 return walk->test_walk(start, end, walk);
180 
181         /*
182          * vma(VM_PFNMAP) doesn't have any valid struct pages behind VM_PFNMAP
183          * range, so we don't walk over it as we do for normal vmas. However,
184          * Some callers are interested in handling hole range and they don't
185          * want to just ignore any single address range. Such users certainly
186          * define their ->pte_hole() callbacks, so let's delegate them to handle
187          * vma(VM_PFNMAP).
188          */
189         if (vma->vm_flags & VM_PFNMAP) {
190                 int err = 1;
191                 if (walk->pte_hole)
192                         err = walk->pte_hole(start, end, walk);
193                 return err ? err : 1;
194         }
195         return 0;
196 }
197 
198 static int __walk_page_range(unsigned long start, unsigned long end,
199                         struct mm_walk *walk)
200 {
201         int err = 0;
202         struct vm_area_struct *vma = walk->vma;
203 
204         if (vma && is_vm_hugetlb_page(vma)) {
205                 if (walk->hugetlb_entry)
206                         err = walk_hugetlb_range(start, end, walk);
207         } else
208                 err = walk_pgd_range(start, end, walk);
209 
210         return err;
211 }
212 
213 /**
214  * walk_page_range - walk page table with caller specific callbacks
215  *
216  * Recursively walk the page table tree of the process represented by @walk->mm
217  * within the virtual address range [@start, @end). During walking, we can do
218  * some caller-specific works for each entry, by setting up pmd_entry(),
219  * pte_entry(), and/or hugetlb_entry(). If you don't set up for some of these
220  * callbacks, the associated entries/pages are just ignored.
221  * The return values of these callbacks are commonly defined like below:
222  *  - 0  : succeeded to handle the current entry, and if you don't reach the
223  *         end address yet, continue to walk.
224  *  - >0 : succeeded to handle the current entry, and return to the caller
225  *         with caller specific value.
226  *  - <0 : failed to handle the current entry, and return to the caller
227  *         with error code.
228  *
229  * Before starting to walk page table, some callers want to check whether
230  * they really want to walk over the current vma, typically by checking
231  * its vm_flags. walk_page_test() and @walk->test_walk() are used for this
232  * purpose.
233  *
234  * struct mm_walk keeps current values of some common data like vma and pmd,
235  * which are useful for the access from callbacks. If you want to pass some
236  * caller-specific data to callbacks, @walk->private should be helpful.
237  *
238  * Locking:
239  *   Callers of walk_page_range() and walk_page_vma() should hold
240  *   @walk->mm->mmap_sem, because these function traverse vma list and/or
241  *   access to vma's data.
242  */
243 int walk_page_range(unsigned long start, unsigned long end,
244                     struct mm_walk *walk)
245 {
246         int err = 0;
247         unsigned long next;
248         struct vm_area_struct *vma;
249 
250         if (start >= end)
251                 return -EINVAL;
252 
253         if (!walk->mm)
254                 return -EINVAL;
255 
256         VM_BUG_ON_MM(!rwsem_is_locked(&walk->mm->mmap_sem), walk->mm);
257 
258         vma = find_vma(walk->mm, start);
259         do {
260                 if (!vma) { /* after the last vma */
261                         walk->vma = NULL;
262                         next = end;
263                 } else if (start < vma->vm_start) { /* outside vma */
264                         walk->vma = NULL;
265                         next = min(end, vma->vm_start);
266                 } else { /* inside vma */
267                         walk->vma = vma;
268                         next = min(end, vma->vm_end);
269                         vma = vma->vm_next;
270 
271                         err = walk_page_test(start, next, walk);
272                         if (err > 0) {
273                                 /*
274                                  * positive return values are purely for
275                                  * controlling the pagewalk, so should never
276                                  * be passed to the callers.
277                                  */
278                                 err = 0;
279                                 continue;
280                         }
281                         if (err < 0)
282                                 break;
283                 }
284                 if (walk->vma || walk->pte_hole)
285                         err = __walk_page_range(start, next, walk);
286                 if (err)
287                         break;
288         } while (start = next, start < end);
289         return err;
290 }
291 
292 int walk_page_vma(struct vm_area_struct *vma, struct mm_walk *walk)
293 {
294         int err;
295 
296         if (!walk->mm)
297                 return -EINVAL;
298 
299         VM_BUG_ON(!rwsem_is_locked(&walk->mm->mmap_sem));
300         VM_BUG_ON(!vma);
301         walk->vma = vma;
302         err = walk_page_test(vma->vm_start, vma->vm_end, walk);
303         if (err > 0)
304                 return 0;
305         if (err < 0)
306                 return err;
307         return __walk_page_range(vma->vm_start, vma->vm_end, walk);
308 }
309 

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