blob: cc5a9e7adea77ff50e8c538b36686db466bffb54 [file] [log] [blame]
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -07001#include <linux/kernel.h>
2#include <linux/errno.h>
3#include <linux/err.h>
4#include <linux/spinlock.h>
5
6#include <linux/hugetlb.h>
7#include <linux/mm.h>
8#include <linux/pagemap.h>
9#include <linux/rmap.h>
10#include <linux/swap.h>
11#include <linux/swapops.h>
12
13#include "internal.h"
14
Kirill A. Shutemov69e68b42014-06-04 16:08:11 -070015static struct page *no_page_table(struct vm_area_struct *vma,
16 unsigned int flags)
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -070017{
Kirill A. Shutemov69e68b42014-06-04 16:08:11 -070018 /*
19 * When core dumping an enormous anonymous area that nobody
20 * has touched so far, we don't want to allocate unnecessary pages or
21 * page tables. Return error instead of NULL to skip handle_mm_fault,
22 * then get_dump_page() will return NULL to leave a hole in the dump.
23 * But we can only make this optimization where a hole would surely
24 * be zero-filled if handle_mm_fault() actually did handle it.
25 */
26 if ((flags & FOLL_DUMP) && (!vma->vm_ops || !vma->vm_ops->fault))
27 return ERR_PTR(-EFAULT);
28 return NULL;
29}
30
31static struct page *follow_page_pte(struct vm_area_struct *vma,
32 unsigned long address, pmd_t *pmd, unsigned int flags)
33{
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -070034 struct mm_struct *mm = vma->vm_mm;
Kirill A. Shutemov69e68b42014-06-04 16:08:11 -070035 struct page *page;
36 spinlock_t *ptl;
37 pte_t *ptep, pte;
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -070038
Kirill A. Shutemov69e68b42014-06-04 16:08:11 -070039retry:
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -070040 if (unlikely(pmd_bad(*pmd)))
Kirill A. Shutemov69e68b42014-06-04 16:08:11 -070041 return no_page_table(vma, flags);
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -070042
43 ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -070044 pte = *ptep;
45 if (!pte_present(pte)) {
46 swp_entry_t entry;
47 /*
48 * KSM's break_ksm() relies upon recognizing a ksm page
49 * even while it is being migrated, so for that case we
50 * need migration_entry_wait().
51 */
52 if (likely(!(flags & FOLL_MIGRATION)))
53 goto no_page;
54 if (pte_none(pte) || pte_file(pte))
55 goto no_page;
56 entry = pte_to_swp_entry(pte);
57 if (!is_migration_entry(entry))
58 goto no_page;
59 pte_unmap_unlock(ptep, ptl);
60 migration_entry_wait(mm, pmd, address);
Kirill A. Shutemov69e68b42014-06-04 16:08:11 -070061 goto retry;
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -070062 }
63 if ((flags & FOLL_NUMA) && pte_numa(pte))
64 goto no_page;
Kirill A. Shutemov69e68b42014-06-04 16:08:11 -070065 if ((flags & FOLL_WRITE) && !pte_write(pte)) {
66 pte_unmap_unlock(ptep, ptl);
67 return NULL;
68 }
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -070069
70 page = vm_normal_page(vma, address, pte);
71 if (unlikely(!page)) {
72 if ((flags & FOLL_DUMP) ||
73 !is_zero_pfn(pte_pfn(pte)))
74 goto bad_page;
75 page = pte_page(pte);
76 }
77
78 if (flags & FOLL_GET)
79 get_page_foll(page);
80 if (flags & FOLL_TOUCH) {
81 if ((flags & FOLL_WRITE) &&
82 !pte_dirty(pte) && !PageDirty(page))
83 set_page_dirty(page);
84 /*
85 * pte_mkyoung() would be more correct here, but atomic care
86 * is needed to avoid losing the dirty bit: it is easier to use
87 * mark_page_accessed().
88 */
89 mark_page_accessed(page);
90 }
91 if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
92 /*
93 * The preliminary mapping check is mainly to avoid the
94 * pointless overhead of lock_page on the ZERO_PAGE
95 * which might bounce very badly if there is contention.
96 *
97 * If the page is already locked, we don't need to
98 * handle it now - vmscan will handle it later if and
99 * when it attempts to reclaim the page.
100 */
101 if (page->mapping && trylock_page(page)) {
102 lru_add_drain(); /* push cached pages to LRU */
103 /*
104 * Because we lock page here, and migration is
105 * blocked by the pte's page reference, and we
106 * know the page is still mapped, we don't even
107 * need to check for file-cache page truncation.
108 */
109 mlock_vma_page(page);
110 unlock_page(page);
111 }
112 }
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700113 pte_unmap_unlock(ptep, ptl);
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700114 return page;
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700115bad_page:
116 pte_unmap_unlock(ptep, ptl);
117 return ERR_PTR(-EFAULT);
118
119no_page:
120 pte_unmap_unlock(ptep, ptl);
121 if (!pte_none(pte))
Kirill A. Shutemov69e68b42014-06-04 16:08:11 -0700122 return NULL;
123 return no_page_table(vma, flags);
124}
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700125
Kirill A. Shutemov69e68b42014-06-04 16:08:11 -0700126/**
127 * follow_page_mask - look up a page descriptor from a user-virtual address
128 * @vma: vm_area_struct mapping @address
129 * @address: virtual address to look up
130 * @flags: flags modifying lookup behaviour
131 * @page_mask: on output, *page_mask is set according to the size of the page
132 *
133 * @flags can have FOLL_ flags set, defined in <linux/mm.h>
134 *
135 * Returns the mapped (struct page *), %NULL if no mapping exists, or
136 * an error pointer if there is a mapping to something not represented
137 * by a page descriptor (see also vm_normal_page()).
138 */
139struct page *follow_page_mask(struct vm_area_struct *vma,
140 unsigned long address, unsigned int flags,
141 unsigned int *page_mask)
142{
143 pgd_t *pgd;
144 pud_t *pud;
145 pmd_t *pmd;
146 spinlock_t *ptl;
147 struct page *page;
148 struct mm_struct *mm = vma->vm_mm;
149
150 *page_mask = 0;
151
152 page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
153 if (!IS_ERR(page)) {
154 BUG_ON(flags & FOLL_GET);
155 return page;
156 }
157
158 pgd = pgd_offset(mm, address);
159 if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
160 return no_page_table(vma, flags);
161
162 pud = pud_offset(pgd, address);
163 if (pud_none(*pud))
164 return no_page_table(vma, flags);
165 if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB) {
166 if (flags & FOLL_GET)
167 return NULL;
168 page = follow_huge_pud(mm, address, pud, flags & FOLL_WRITE);
169 return page;
170 }
171 if (unlikely(pud_bad(*pud)))
172 return no_page_table(vma, flags);
173
174 pmd = pmd_offset(pud, address);
175 if (pmd_none(*pmd))
176 return no_page_table(vma, flags);
177 if (pmd_huge(*pmd) && vma->vm_flags & VM_HUGETLB) {
178 page = follow_huge_pmd(mm, address, pmd, flags & FOLL_WRITE);
179 if (flags & FOLL_GET) {
180 /*
181 * Refcount on tail pages are not well-defined and
182 * shouldn't be taken. The caller should handle a NULL
183 * return when trying to follow tail pages.
184 */
185 if (PageHead(page))
186 get_page(page);
187 else
188 page = NULL;
189 }
190 return page;
191 }
192 if ((flags & FOLL_NUMA) && pmd_numa(*pmd))
193 return no_page_table(vma, flags);
194 if (pmd_trans_huge(*pmd)) {
195 if (flags & FOLL_SPLIT) {
196 split_huge_page_pmd(vma, address, pmd);
197 return follow_page_pte(vma, address, pmd, flags);
198 }
199 ptl = pmd_lock(mm, pmd);
200 if (likely(pmd_trans_huge(*pmd))) {
201 if (unlikely(pmd_trans_splitting(*pmd))) {
202 spin_unlock(ptl);
203 wait_split_huge_page(vma->anon_vma, pmd);
204 } else {
205 page = follow_trans_huge_pmd(vma, address,
206 pmd, flags);
207 spin_unlock(ptl);
208 *page_mask = HPAGE_PMD_NR - 1;
209 return page;
210 }
211 } else
212 spin_unlock(ptl);
213 }
214 return follow_page_pte(vma, address, pmd, flags);
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700215}
216
Kirill A. Shutemovf2b495c2014-06-04 16:08:11 -0700217static int get_gate_page(struct mm_struct *mm, unsigned long address,
218 unsigned int gup_flags, struct vm_area_struct **vma,
219 struct page **page)
220{
221 pgd_t *pgd;
222 pud_t *pud;
223 pmd_t *pmd;
224 pte_t *pte;
225 int ret = -EFAULT;
226
227 /* user gate pages are read-only */
228 if (gup_flags & FOLL_WRITE)
229 return -EFAULT;
230 if (address > TASK_SIZE)
231 pgd = pgd_offset_k(address);
232 else
233 pgd = pgd_offset_gate(mm, address);
234 BUG_ON(pgd_none(*pgd));
235 pud = pud_offset(pgd, address);
236 BUG_ON(pud_none(*pud));
237 pmd = pmd_offset(pud, address);
238 if (pmd_none(*pmd))
239 return -EFAULT;
240 VM_BUG_ON(pmd_trans_huge(*pmd));
241 pte = pte_offset_map(pmd, address);
242 if (pte_none(*pte))
243 goto unmap;
244 *vma = get_gate_vma(mm);
245 if (!page)
246 goto out;
247 *page = vm_normal_page(*vma, address, *pte);
248 if (!*page) {
249 if ((gup_flags & FOLL_DUMP) || !is_zero_pfn(pte_pfn(*pte)))
250 goto unmap;
251 *page = pte_page(*pte);
252 }
253 get_page(*page);
254out:
255 ret = 0;
256unmap:
257 pte_unmap(pte);
258 return ret;
259}
260
Kirill A. Shutemov16744482014-06-04 16:08:12 -0700261static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
262 unsigned long address, unsigned int *flags, int *nonblocking)
263{
264 struct mm_struct *mm = vma->vm_mm;
265 unsigned int fault_flags = 0;
266 int ret;
267
268 /* For mlock, just skip the stack guard page. */
269 if ((*flags & FOLL_MLOCK) &&
270 (stack_guard_page_start(vma, address) ||
271 stack_guard_page_end(vma, address + PAGE_SIZE)))
272 return -ENOENT;
273 if (*flags & FOLL_WRITE)
274 fault_flags |= FAULT_FLAG_WRITE;
275 if (nonblocking)
276 fault_flags |= FAULT_FLAG_ALLOW_RETRY;
277 if (*flags & FOLL_NOWAIT)
278 fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
279
280 ret = handle_mm_fault(mm, vma, address, fault_flags);
281 if (ret & VM_FAULT_ERROR) {
282 if (ret & VM_FAULT_OOM)
283 return -ENOMEM;
284 if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))
285 return *flags & FOLL_HWPOISON ? -EHWPOISON : -EFAULT;
286 if (ret & VM_FAULT_SIGBUS)
287 return -EFAULT;
288 BUG();
289 }
290
291 if (tsk) {
292 if (ret & VM_FAULT_MAJOR)
293 tsk->maj_flt++;
294 else
295 tsk->min_flt++;
296 }
297
298 if (ret & VM_FAULT_RETRY) {
299 if (nonblocking)
300 *nonblocking = 0;
301 return -EBUSY;
302 }
303
304 /*
305 * The VM_FAULT_WRITE bit tells us that do_wp_page has broken COW when
306 * necessary, even if maybe_mkwrite decided not to set pte_write. We
307 * can thus safely do subsequent page lookups as if they were reads.
308 * But only do so when looping for pte_write is futile: in some cases
309 * userspace may also be wanting to write to the gotten user page,
310 * which a read fault here might prevent (a readonly page might get
311 * reCOWed by userspace write).
312 */
313 if ((ret & VM_FAULT_WRITE) && !(vma->vm_flags & VM_WRITE))
314 *flags &= ~FOLL_WRITE;
315 return 0;
316}
317
Kirill A. Shutemovfa5bb202014-06-04 16:08:13 -0700318static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
319{
320 vm_flags_t vm_flags = vma->vm_flags;
321
322 if (vm_flags & (VM_IO | VM_PFNMAP))
323 return -EFAULT;
324
325 if (gup_flags & FOLL_WRITE) {
326 if (!(vm_flags & VM_WRITE)) {
327 if (!(gup_flags & FOLL_FORCE))
328 return -EFAULT;
329 /*
330 * We used to let the write,force case do COW in a
331 * VM_MAYWRITE VM_SHARED !VM_WRITE vma, so ptrace could
332 * set a breakpoint in a read-only mapping of an
333 * executable, without corrupting the file (yet only
334 * when that file had been opened for writing!).
335 * Anon pages in shared mappings are surprising: now
336 * just reject it.
337 */
338 if (!is_cow_mapping(vm_flags)) {
339 WARN_ON_ONCE(vm_flags & VM_MAYWRITE);
340 return -EFAULT;
341 }
342 }
343 } else if (!(vm_flags & VM_READ)) {
344 if (!(gup_flags & FOLL_FORCE))
345 return -EFAULT;
346 /*
347 * Is there actually any vma we can reach here which does not
348 * have VM_MAYREAD set?
349 */
350 if (!(vm_flags & VM_MAYREAD))
351 return -EFAULT;
352 }
353 return 0;
354}
355
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700356/**
357 * __get_user_pages() - pin user pages in memory
358 * @tsk: task_struct of target task
359 * @mm: mm_struct of target mm
360 * @start: starting user address
361 * @nr_pages: number of pages from start to pin
362 * @gup_flags: flags modifying pin behaviour
363 * @pages: array that receives pointers to the pages pinned.
364 * Should be at least nr_pages long. Or NULL, if caller
365 * only intends to ensure the pages are faulted in.
366 * @vmas: array of pointers to vmas corresponding to each page.
367 * Or NULL if the caller does not require them.
368 * @nonblocking: whether waiting for disk IO or mmap_sem contention
369 *
370 * Returns number of pages pinned. This may be fewer than the number
371 * requested. If nr_pages is 0 or negative, returns 0. If no pages
372 * were pinned, returns -errno. Each page returned must be released
373 * with a put_page() call when it is finished with. vmas will only
374 * remain valid while mmap_sem is held.
375 *
376 * Must be called with mmap_sem held for read or write.
377 *
378 * __get_user_pages walks a process's page tables and takes a reference to
379 * each struct page that each user address corresponds to at a given
380 * instant. That is, it takes the page that would be accessed if a user
381 * thread accesses the given user virtual address at that instant.
382 *
383 * This does not guarantee that the page exists in the user mappings when
384 * __get_user_pages returns, and there may even be a completely different
385 * page there in some cases (eg. if mmapped pagecache has been invalidated
386 * and subsequently re faulted). However it does guarantee that the page
387 * won't be freed completely. And mostly callers simply care that the page
388 * contains data that was valid *at some point in time*. Typically, an IO
389 * or similar operation cannot guarantee anything stronger anyway because
390 * locks can't be held over the syscall boundary.
391 *
392 * If @gup_flags & FOLL_WRITE == 0, the page must not be written to. If
393 * the page is written to, set_page_dirty (or set_page_dirty_lock, as
394 * appropriate) must be called after the page is finished with, and
395 * before put_page is called.
396 *
397 * If @nonblocking != NULL, __get_user_pages will not wait for disk IO
398 * or mmap_sem contention, and if waiting is needed to pin all pages,
399 * *@nonblocking will be set to 0.
400 *
401 * In most cases, get_user_pages or get_user_pages_fast should be used
402 * instead of __get_user_pages. __get_user_pages should be used only if
403 * you need some special @gup_flags.
404 */
405long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
406 unsigned long start, unsigned long nr_pages,
407 unsigned int gup_flags, struct page **pages,
408 struct vm_area_struct **vmas, int *nonblocking)
409{
Kirill A. Shutemovfa5bb202014-06-04 16:08:13 -0700410 long i = 0;
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700411 unsigned int page_mask;
Kirill A. Shutemovfa5bb202014-06-04 16:08:13 -0700412 struct vm_area_struct *vma = NULL;
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700413
414 if (!nr_pages)
415 return 0;
416
417 VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));
418
419 /*
420 * If FOLL_FORCE is set then do not force a full fault as the hinting
421 * fault information is unrelated to the reference behaviour of a task
422 * using the address space
423 */
424 if (!(gup_flags & FOLL_FORCE))
425 gup_flags |= FOLL_NUMA;
426
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700427 do {
Kirill A. Shutemovfa5bb202014-06-04 16:08:13 -0700428 struct page *page;
429 unsigned int foll_flags = gup_flags;
430 unsigned int page_increm;
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700431
Kirill A. Shutemovfa5bb202014-06-04 16:08:13 -0700432 /* first iteration or cross vma bound */
433 if (!vma || start >= vma->vm_end) {
434 vma = find_extend_vma(mm, start);
435 if (!vma && in_gate_area(mm, start)) {
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700436 int ret;
Kirill A. Shutemovfa5bb202014-06-04 16:08:13 -0700437 ret = get_gate_page(mm, start & PAGE_MASK,
438 gup_flags, &vma,
439 pages ? &pages[i] : NULL);
440 if (ret)
441 return i ? : ret;
442 page_mask = 0;
443 goto next_page;
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700444 }
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700445
Kirill A. Shutemovfa5bb202014-06-04 16:08:13 -0700446 if (!vma || check_vma_flags(vma, gup_flags))
447 return i ? : -EFAULT;
448 if (is_vm_hugetlb_page(vma)) {
449 i = follow_hugetlb_page(mm, vma, pages, vmas,
450 &start, &nr_pages, i,
451 gup_flags);
452 continue;
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700453 }
Kirill A. Shutemovfa5bb202014-06-04 16:08:13 -0700454 }
455retry:
456 /*
457 * If we have a pending SIGKILL, don't keep faulting pages and
458 * potentially allocating memory.
459 */
460 if (unlikely(fatal_signal_pending(current)))
461 return i ? i : -ERESTARTSYS;
462 cond_resched();
463 page = follow_page_mask(vma, start, foll_flags, &page_mask);
464 if (!page) {
465 int ret;
466 ret = faultin_page(tsk, vma, start, &foll_flags,
467 nonblocking);
468 switch (ret) {
469 case 0:
470 goto retry;
471 case -EFAULT:
472 case -ENOMEM:
473 case -EHWPOISON:
474 return i ? i : ret;
475 case -EBUSY:
476 return i;
477 case -ENOENT:
478 goto next_page;
479 }
480 BUG();
481 }
482 if (IS_ERR(page))
483 return i ? i : PTR_ERR(page);
484 if (pages) {
485 pages[i] = page;
486 flush_anon_page(vma, page, start);
487 flush_dcache_page(page);
488 page_mask = 0;
489 }
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700490next_page:
Kirill A. Shutemovfa5bb202014-06-04 16:08:13 -0700491 if (vmas) {
492 vmas[i] = vma;
493 page_mask = 0;
494 }
495 page_increm = 1 + (~(start >> PAGE_SHIFT) & page_mask);
496 if (page_increm > nr_pages)
497 page_increm = nr_pages;
498 i += page_increm;
499 start += page_increm * PAGE_SIZE;
500 nr_pages -= page_increm;
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700501 } while (nr_pages);
502 return i;
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700503}
504EXPORT_SYMBOL(__get_user_pages);
505
506/*
507 * fixup_user_fault() - manually resolve a user page fault
508 * @tsk: the task_struct to use for page fault accounting, or
509 * NULL if faults are not to be recorded.
510 * @mm: mm_struct of target mm
511 * @address: user address
512 * @fault_flags:flags to pass down to handle_mm_fault()
513 *
514 * This is meant to be called in the specific scenario where for locking reasons
515 * we try to access user memory in atomic context (within a pagefault_disable()
516 * section), this returns -EFAULT, and we want to resolve the user fault before
517 * trying again.
518 *
519 * Typically this is meant to be used by the futex code.
520 *
521 * The main difference with get_user_pages() is that this function will
522 * unconditionally call handle_mm_fault() which will in turn perform all the
523 * necessary SW fixup of the dirty and young bits in the PTE, while
524 * handle_mm_fault() only guarantees to update these in the struct page.
525 *
526 * This is important for some architectures where those bits also gate the
527 * access permission to the page because they are maintained in software. On
528 * such architectures, gup() will not be enough to make a subsequent access
529 * succeed.
530 *
531 * This should be called with the mm_sem held for read.
532 */
533int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
534 unsigned long address, unsigned int fault_flags)
535{
536 struct vm_area_struct *vma;
537 vm_flags_t vm_flags;
538 int ret;
539
540 vma = find_extend_vma(mm, address);
541 if (!vma || address < vma->vm_start)
542 return -EFAULT;
543
544 vm_flags = (fault_flags & FAULT_FLAG_WRITE) ? VM_WRITE : VM_READ;
545 if (!(vm_flags & vma->vm_flags))
546 return -EFAULT;
547
548 ret = handle_mm_fault(mm, vma, address, fault_flags);
549 if (ret & VM_FAULT_ERROR) {
550 if (ret & VM_FAULT_OOM)
551 return -ENOMEM;
552 if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))
553 return -EHWPOISON;
554 if (ret & VM_FAULT_SIGBUS)
555 return -EFAULT;
556 BUG();
557 }
558 if (tsk) {
559 if (ret & VM_FAULT_MAJOR)
560 tsk->maj_flt++;
561 else
562 tsk->min_flt++;
563 }
564 return 0;
565}
566
567/*
568 * get_user_pages() - pin user pages in memory
569 * @tsk: the task_struct to use for page fault accounting, or
570 * NULL if faults are not to be recorded.
571 * @mm: mm_struct of target mm
572 * @start: starting user address
573 * @nr_pages: number of pages from start to pin
574 * @write: whether pages will be written to by the caller
575 * @force: whether to force access even when user mapping is currently
576 * protected (but never forces write access to shared mapping).
577 * @pages: array that receives pointers to the pages pinned.
578 * Should be at least nr_pages long. Or NULL, if caller
579 * only intends to ensure the pages are faulted in.
580 * @vmas: array of pointers to vmas corresponding to each page.
581 * Or NULL if the caller does not require them.
582 *
583 * Returns number of pages pinned. This may be fewer than the number
584 * requested. If nr_pages is 0 or negative, returns 0. If no pages
585 * were pinned, returns -errno. Each page returned must be released
586 * with a put_page() call when it is finished with. vmas will only
587 * remain valid while mmap_sem is held.
588 *
589 * Must be called with mmap_sem held for read or write.
590 *
591 * get_user_pages walks a process's page tables and takes a reference to
592 * each struct page that each user address corresponds to at a given
593 * instant. That is, it takes the page that would be accessed if a user
594 * thread accesses the given user virtual address at that instant.
595 *
596 * This does not guarantee that the page exists in the user mappings when
597 * get_user_pages returns, and there may even be a completely different
598 * page there in some cases (eg. if mmapped pagecache has been invalidated
599 * and subsequently re faulted). However it does guarantee that the page
600 * won't be freed completely. And mostly callers simply care that the page
601 * contains data that was valid *at some point in time*. Typically, an IO
602 * or similar operation cannot guarantee anything stronger anyway because
603 * locks can't be held over the syscall boundary.
604 *
605 * If write=0, the page must not be written to. If the page is written to,
606 * set_page_dirty (or set_page_dirty_lock, as appropriate) must be called
607 * after the page is finished with, and before put_page is called.
608 *
609 * get_user_pages is typically used for fewer-copy IO operations, to get a
610 * handle on the memory by some means other than accesses via the user virtual
611 * addresses. The pages may be submitted for DMA to devices or accessed via
612 * their kernel linear mapping (via the kmap APIs). Care should be taken to
613 * use the correct cache flushing APIs.
614 *
615 * See also get_user_pages_fast, for performance critical applications.
616 */
617long get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
618 unsigned long start, unsigned long nr_pages, int write,
619 int force, struct page **pages, struct vm_area_struct **vmas)
620{
621 int flags = FOLL_TOUCH;
622
623 if (pages)
624 flags |= FOLL_GET;
625 if (write)
626 flags |= FOLL_WRITE;
627 if (force)
628 flags |= FOLL_FORCE;
629
630 return __get_user_pages(tsk, mm, start, nr_pages, flags, pages, vmas,
631 NULL);
632}
633EXPORT_SYMBOL(get_user_pages);
634
635/**
636 * get_dump_page() - pin user page in memory while writing it to core dump
637 * @addr: user address
638 *
639 * Returns struct page pointer of user page pinned for dump,
640 * to be freed afterwards by page_cache_release() or put_page().
641 *
642 * Returns NULL on any kind of failure - a hole must then be inserted into
643 * the corefile, to preserve alignment with its headers; and also returns
644 * NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
645 * allowing a hole to be left in the corefile to save diskspace.
646 *
647 * Called without mmap_sem, but after all other threads have been killed.
648 */
649#ifdef CONFIG_ELF_CORE
650struct page *get_dump_page(unsigned long addr)
651{
652 struct vm_area_struct *vma;
653 struct page *page;
654
655 if (__get_user_pages(current, current->mm, addr, 1,
656 FOLL_FORCE | FOLL_DUMP | FOLL_GET, &page, &vma,
657 NULL) < 1)
658 return NULL;
659 flush_cache_page(vma, addr, page_to_pfn(page));
660 return page;
661}
662#endif /* CONFIG_ELF_CORE */