blob: 91d044b1600dd6b216decb62ca9f1bd7ef152c52 [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
Paul Cassella9a95f3c2014-08-06 16:07:24 -0700261/*
262 * mmap_sem must be held on entry. If @nonblocking != NULL and
263 * *@flags does not include FOLL_NOWAIT, the mmap_sem may be released.
264 * If it is, *@nonblocking will be set to 0 and -EBUSY returned.
265 */
Kirill A. Shutemov16744482014-06-04 16:08:12 -0700266static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
267 unsigned long address, unsigned int *flags, int *nonblocking)
268{
269 struct mm_struct *mm = vma->vm_mm;
270 unsigned int fault_flags = 0;
271 int ret;
272
273 /* For mlock, just skip the stack guard page. */
274 if ((*flags & FOLL_MLOCK) &&
275 (stack_guard_page_start(vma, address) ||
276 stack_guard_page_end(vma, address + PAGE_SIZE)))
277 return -ENOENT;
278 if (*flags & FOLL_WRITE)
279 fault_flags |= FAULT_FLAG_WRITE;
280 if (nonblocking)
281 fault_flags |= FAULT_FLAG_ALLOW_RETRY;
282 if (*flags & FOLL_NOWAIT)
283 fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
284
285 ret = handle_mm_fault(mm, vma, address, fault_flags);
286 if (ret & VM_FAULT_ERROR) {
287 if (ret & VM_FAULT_OOM)
288 return -ENOMEM;
289 if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))
290 return *flags & FOLL_HWPOISON ? -EHWPOISON : -EFAULT;
291 if (ret & VM_FAULT_SIGBUS)
292 return -EFAULT;
293 BUG();
294 }
295
296 if (tsk) {
297 if (ret & VM_FAULT_MAJOR)
298 tsk->maj_flt++;
299 else
300 tsk->min_flt++;
301 }
302
303 if (ret & VM_FAULT_RETRY) {
304 if (nonblocking)
305 *nonblocking = 0;
306 return -EBUSY;
307 }
308
309 /*
310 * The VM_FAULT_WRITE bit tells us that do_wp_page has broken COW when
311 * necessary, even if maybe_mkwrite decided not to set pte_write. We
312 * can thus safely do subsequent page lookups as if they were reads.
313 * But only do so when looping for pte_write is futile: in some cases
314 * userspace may also be wanting to write to the gotten user page,
315 * which a read fault here might prevent (a readonly page might get
316 * reCOWed by userspace write).
317 */
318 if ((ret & VM_FAULT_WRITE) && !(vma->vm_flags & VM_WRITE))
319 *flags &= ~FOLL_WRITE;
320 return 0;
321}
322
Kirill A. Shutemovfa5bb202014-06-04 16:08:13 -0700323static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
324{
325 vm_flags_t vm_flags = vma->vm_flags;
326
327 if (vm_flags & (VM_IO | VM_PFNMAP))
328 return -EFAULT;
329
330 if (gup_flags & FOLL_WRITE) {
331 if (!(vm_flags & VM_WRITE)) {
332 if (!(gup_flags & FOLL_FORCE))
333 return -EFAULT;
334 /*
335 * We used to let the write,force case do COW in a
336 * VM_MAYWRITE VM_SHARED !VM_WRITE vma, so ptrace could
337 * set a breakpoint in a read-only mapping of an
338 * executable, without corrupting the file (yet only
339 * when that file had been opened for writing!).
340 * Anon pages in shared mappings are surprising: now
341 * just reject it.
342 */
343 if (!is_cow_mapping(vm_flags)) {
344 WARN_ON_ONCE(vm_flags & VM_MAYWRITE);
345 return -EFAULT;
346 }
347 }
348 } else if (!(vm_flags & VM_READ)) {
349 if (!(gup_flags & FOLL_FORCE))
350 return -EFAULT;
351 /*
352 * Is there actually any vma we can reach here which does not
353 * have VM_MAYREAD set?
354 */
355 if (!(vm_flags & VM_MAYREAD))
356 return -EFAULT;
357 }
358 return 0;
359}
360
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700361/**
362 * __get_user_pages() - pin user pages in memory
363 * @tsk: task_struct of target task
364 * @mm: mm_struct of target mm
365 * @start: starting user address
366 * @nr_pages: number of pages from start to pin
367 * @gup_flags: flags modifying pin behaviour
368 * @pages: array that receives pointers to the pages pinned.
369 * Should be at least nr_pages long. Or NULL, if caller
370 * only intends to ensure the pages are faulted in.
371 * @vmas: array of pointers to vmas corresponding to each page.
372 * Or NULL if the caller does not require them.
373 * @nonblocking: whether waiting for disk IO or mmap_sem contention
374 *
375 * Returns number of pages pinned. This may be fewer than the number
376 * requested. If nr_pages is 0 or negative, returns 0. If no pages
377 * were pinned, returns -errno. Each page returned must be released
378 * with a put_page() call when it is finished with. vmas will only
379 * remain valid while mmap_sem is held.
380 *
Paul Cassella9a95f3c2014-08-06 16:07:24 -0700381 * Must be called with mmap_sem held. It may be released. See below.
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700382 *
383 * __get_user_pages walks a process's page tables and takes a reference to
384 * each struct page that each user address corresponds to at a given
385 * instant. That is, it takes the page that would be accessed if a user
386 * thread accesses the given user virtual address at that instant.
387 *
388 * This does not guarantee that the page exists in the user mappings when
389 * __get_user_pages returns, and there may even be a completely different
390 * page there in some cases (eg. if mmapped pagecache has been invalidated
391 * and subsequently re faulted). However it does guarantee that the page
392 * won't be freed completely. And mostly callers simply care that the page
393 * contains data that was valid *at some point in time*. Typically, an IO
394 * or similar operation cannot guarantee anything stronger anyway because
395 * locks can't be held over the syscall boundary.
396 *
397 * If @gup_flags & FOLL_WRITE == 0, the page must not be written to. If
398 * the page is written to, set_page_dirty (or set_page_dirty_lock, as
399 * appropriate) must be called after the page is finished with, and
400 * before put_page is called.
401 *
402 * If @nonblocking != NULL, __get_user_pages will not wait for disk IO
403 * or mmap_sem contention, and if waiting is needed to pin all pages,
Paul Cassella9a95f3c2014-08-06 16:07:24 -0700404 * *@nonblocking will be set to 0. Further, if @gup_flags does not
405 * include FOLL_NOWAIT, the mmap_sem will be released via up_read() in
406 * this case.
407 *
408 * A caller using such a combination of @nonblocking and @gup_flags
409 * must therefore hold the mmap_sem for reading only, and recognize
410 * when it's been released. Otherwise, it must be held for either
411 * reading or writing and will not be released.
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700412 *
413 * In most cases, get_user_pages or get_user_pages_fast should be used
414 * instead of __get_user_pages. __get_user_pages should be used only if
415 * you need some special @gup_flags.
416 */
417long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
418 unsigned long start, unsigned long nr_pages,
419 unsigned int gup_flags, struct page **pages,
420 struct vm_area_struct **vmas, int *nonblocking)
421{
Kirill A. Shutemovfa5bb202014-06-04 16:08:13 -0700422 long i = 0;
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700423 unsigned int page_mask;
Kirill A. Shutemovfa5bb202014-06-04 16:08:13 -0700424 struct vm_area_struct *vma = NULL;
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700425
426 if (!nr_pages)
427 return 0;
428
429 VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));
430
431 /*
432 * If FOLL_FORCE is set then do not force a full fault as the hinting
433 * fault information is unrelated to the reference behaviour of a task
434 * using the address space
435 */
436 if (!(gup_flags & FOLL_FORCE))
437 gup_flags |= FOLL_NUMA;
438
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700439 do {
Kirill A. Shutemovfa5bb202014-06-04 16:08:13 -0700440 struct page *page;
441 unsigned int foll_flags = gup_flags;
442 unsigned int page_increm;
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700443
Kirill A. Shutemovfa5bb202014-06-04 16:08:13 -0700444 /* first iteration or cross vma bound */
445 if (!vma || start >= vma->vm_end) {
446 vma = find_extend_vma(mm, start);
447 if (!vma && in_gate_area(mm, start)) {
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700448 int ret;
Kirill A. Shutemovfa5bb202014-06-04 16:08:13 -0700449 ret = get_gate_page(mm, start & PAGE_MASK,
450 gup_flags, &vma,
451 pages ? &pages[i] : NULL);
452 if (ret)
453 return i ? : ret;
454 page_mask = 0;
455 goto next_page;
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700456 }
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700457
Kirill A. Shutemovfa5bb202014-06-04 16:08:13 -0700458 if (!vma || check_vma_flags(vma, gup_flags))
459 return i ? : -EFAULT;
460 if (is_vm_hugetlb_page(vma)) {
461 i = follow_hugetlb_page(mm, vma, pages, vmas,
462 &start, &nr_pages, i,
463 gup_flags);
464 continue;
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700465 }
Kirill A. Shutemovfa5bb202014-06-04 16:08:13 -0700466 }
467retry:
468 /*
469 * If we have a pending SIGKILL, don't keep faulting pages and
470 * potentially allocating memory.
471 */
472 if (unlikely(fatal_signal_pending(current)))
473 return i ? i : -ERESTARTSYS;
474 cond_resched();
475 page = follow_page_mask(vma, start, foll_flags, &page_mask);
476 if (!page) {
477 int ret;
478 ret = faultin_page(tsk, vma, start, &foll_flags,
479 nonblocking);
480 switch (ret) {
481 case 0:
482 goto retry;
483 case -EFAULT:
484 case -ENOMEM:
485 case -EHWPOISON:
486 return i ? i : ret;
487 case -EBUSY:
488 return i;
489 case -ENOENT:
490 goto next_page;
491 }
492 BUG();
493 }
494 if (IS_ERR(page))
495 return i ? i : PTR_ERR(page);
496 if (pages) {
497 pages[i] = page;
498 flush_anon_page(vma, page, start);
499 flush_dcache_page(page);
500 page_mask = 0;
501 }
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700502next_page:
Kirill A. Shutemovfa5bb202014-06-04 16:08:13 -0700503 if (vmas) {
504 vmas[i] = vma;
505 page_mask = 0;
506 }
507 page_increm = 1 + (~(start >> PAGE_SHIFT) & page_mask);
508 if (page_increm > nr_pages)
509 page_increm = nr_pages;
510 i += page_increm;
511 start += page_increm * PAGE_SIZE;
512 nr_pages -= page_increm;
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700513 } while (nr_pages);
514 return i;
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700515}
516EXPORT_SYMBOL(__get_user_pages);
517
518/*
519 * fixup_user_fault() - manually resolve a user page fault
520 * @tsk: the task_struct to use for page fault accounting, or
521 * NULL if faults are not to be recorded.
522 * @mm: mm_struct of target mm
523 * @address: user address
524 * @fault_flags:flags to pass down to handle_mm_fault()
525 *
526 * This is meant to be called in the specific scenario where for locking reasons
527 * we try to access user memory in atomic context (within a pagefault_disable()
528 * section), this returns -EFAULT, and we want to resolve the user fault before
529 * trying again.
530 *
531 * Typically this is meant to be used by the futex code.
532 *
533 * The main difference with get_user_pages() is that this function will
534 * unconditionally call handle_mm_fault() which will in turn perform all the
535 * necessary SW fixup of the dirty and young bits in the PTE, while
536 * handle_mm_fault() only guarantees to update these in the struct page.
537 *
538 * This is important for some architectures where those bits also gate the
539 * access permission to the page because they are maintained in software. On
540 * such architectures, gup() will not be enough to make a subsequent access
541 * succeed.
542 *
Paul Cassella9a95f3c2014-08-06 16:07:24 -0700543 * This has the same semantics wrt the @mm->mmap_sem as does filemap_fault().
Kirill A. Shutemov4bbd4c72014-06-04 16:08:10 -0700544 */
545int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
546 unsigned long address, unsigned int fault_flags)
547{
548 struct vm_area_struct *vma;
549 vm_flags_t vm_flags;
550 int ret;
551
552 vma = find_extend_vma(mm, address);
553 if (!vma || address < vma->vm_start)
554 return -EFAULT;
555
556 vm_flags = (fault_flags & FAULT_FLAG_WRITE) ? VM_WRITE : VM_READ;
557 if (!(vm_flags & vma->vm_flags))
558 return -EFAULT;
559
560 ret = handle_mm_fault(mm, vma, address, fault_flags);
561 if (ret & VM_FAULT_ERROR) {
562 if (ret & VM_FAULT_OOM)
563 return -ENOMEM;
564 if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))
565 return -EHWPOISON;
566 if (ret & VM_FAULT_SIGBUS)
567 return -EFAULT;
568 BUG();
569 }
570 if (tsk) {
571 if (ret & VM_FAULT_MAJOR)
572 tsk->maj_flt++;
573 else
574 tsk->min_flt++;
575 }
576 return 0;
577}
578
579/*
580 * get_user_pages() - pin user pages in memory
581 * @tsk: the task_struct to use for page fault accounting, or
582 * NULL if faults are not to be recorded.
583 * @mm: mm_struct of target mm
584 * @start: starting user address
585 * @nr_pages: number of pages from start to pin
586 * @write: whether pages will be written to by the caller
587 * @force: whether to force access even when user mapping is currently
588 * protected (but never forces write access to shared mapping).
589 * @pages: array that receives pointers to the pages pinned.
590 * Should be at least nr_pages long. Or NULL, if caller
591 * only intends to ensure the pages are faulted in.
592 * @vmas: array of pointers to vmas corresponding to each page.
593 * Or NULL if the caller does not require them.
594 *
595 * Returns number of pages pinned. This may be fewer than the number
596 * requested. If nr_pages is 0 or negative, returns 0. If no pages
597 * were pinned, returns -errno. Each page returned must be released
598 * with a put_page() call when it is finished with. vmas will only
599 * remain valid while mmap_sem is held.
600 *
601 * Must be called with mmap_sem held for read or write.
602 *
603 * get_user_pages walks a process's page tables and takes a reference to
604 * each struct page that each user address corresponds to at a given
605 * instant. That is, it takes the page that would be accessed if a user
606 * thread accesses the given user virtual address at that instant.
607 *
608 * This does not guarantee that the page exists in the user mappings when
609 * get_user_pages returns, and there may even be a completely different
610 * page there in some cases (eg. if mmapped pagecache has been invalidated
611 * and subsequently re faulted). However it does guarantee that the page
612 * won't be freed completely. And mostly callers simply care that the page
613 * contains data that was valid *at some point in time*. Typically, an IO
614 * or similar operation cannot guarantee anything stronger anyway because
615 * locks can't be held over the syscall boundary.
616 *
617 * If write=0, the page must not be written to. If the page is written to,
618 * set_page_dirty (or set_page_dirty_lock, as appropriate) must be called
619 * after the page is finished with, and before put_page is called.
620 *
621 * get_user_pages is typically used for fewer-copy IO operations, to get a
622 * handle on the memory by some means other than accesses via the user virtual
623 * addresses. The pages may be submitted for DMA to devices or accessed via
624 * their kernel linear mapping (via the kmap APIs). Care should be taken to
625 * use the correct cache flushing APIs.
626 *
627 * See also get_user_pages_fast, for performance critical applications.
628 */
629long get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
630 unsigned long start, unsigned long nr_pages, int write,
631 int force, struct page **pages, struct vm_area_struct **vmas)
632{
633 int flags = FOLL_TOUCH;
634
635 if (pages)
636 flags |= FOLL_GET;
637 if (write)
638 flags |= FOLL_WRITE;
639 if (force)
640 flags |= FOLL_FORCE;
641
642 return __get_user_pages(tsk, mm, start, nr_pages, flags, pages, vmas,
643 NULL);
644}
645EXPORT_SYMBOL(get_user_pages);
646
647/**
648 * get_dump_page() - pin user page in memory while writing it to core dump
649 * @addr: user address
650 *
651 * Returns struct page pointer of user page pinned for dump,
652 * to be freed afterwards by page_cache_release() or put_page().
653 *
654 * Returns NULL on any kind of failure - a hole must then be inserted into
655 * the corefile, to preserve alignment with its headers; and also returns
656 * NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
657 * allowing a hole to be left in the corefile to save diskspace.
658 *
659 * Called without mmap_sem, but after all other threads have been killed.
660 */
661#ifdef CONFIG_ELF_CORE
662struct page *get_dump_page(unsigned long addr)
663{
664 struct vm_area_struct *vma;
665 struct page *page;
666
667 if (__get_user_pages(current, current->mm, addr, 1,
668 FOLL_FORCE | FOLL_DUMP | FOLL_GET, &page, &vma,
669 NULL) < 1)
670 return NULL;
671 flush_cache_page(vma, addr, page_to_pfn(page));
672 return page;
673}
674#endif /* CONFIG_ELF_CORE */