Version:  2.0.40 2.2.26 2.4.37 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

Linux/mm/gup.c

  1 #include <linux/kernel.h>
  2 #include <linux/errno.h>
  3 #include <linux/err.h>
  4 #include <linux/spinlock.h>
  5 
  6 #include <linux/mm.h>
  7 #include <linux/memremap.h>
  8 #include <linux/pagemap.h>
  9 #include <linux/rmap.h>
 10 #include <linux/swap.h>
 11 #include <linux/swapops.h>
 12 
 13 #include <linux/sched.h>
 14 #include <linux/rwsem.h>
 15 #include <linux/hugetlb.h>
 16 
 17 #include <asm/mmu_context.h>
 18 #include <asm/pgtable.h>
 19 #include <asm/tlbflush.h>
 20 
 21 #include "internal.h"
 22 
 23 static struct page *no_page_table(struct vm_area_struct *vma,
 24                 unsigned int flags)
 25 {
 26         /*
 27          * When core dumping an enormous anonymous area that nobody
 28          * has touched so far, we don't want to allocate unnecessary pages or
 29          * page tables.  Return error instead of NULL to skip handle_mm_fault,
 30          * then get_dump_page() will return NULL to leave a hole in the dump.
 31          * But we can only make this optimization where a hole would surely
 32          * be zero-filled if handle_mm_fault() actually did handle it.
 33          */
 34         if ((flags & FOLL_DUMP) && (!vma->vm_ops || !vma->vm_ops->fault))
 35                 return ERR_PTR(-EFAULT);
 36         return NULL;
 37 }
 38 
 39 static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
 40                 pte_t *pte, unsigned int flags)
 41 {
 42         /* No page to get reference */
 43         if (flags & FOLL_GET)
 44                 return -EFAULT;
 45 
 46         if (flags & FOLL_TOUCH) {
 47                 pte_t entry = *pte;
 48 
 49                 if (flags & FOLL_WRITE)
 50                         entry = pte_mkdirty(entry);
 51                 entry = pte_mkyoung(entry);
 52 
 53                 if (!pte_same(*pte, entry)) {
 54                         set_pte_at(vma->vm_mm, address, pte, entry);
 55                         update_mmu_cache(vma, address, pte);
 56                 }
 57         }
 58 
 59         /* Proper page table entry exists, but no corresponding struct page */
 60         return -EEXIST;
 61 }
 62 
 63 /*
 64  * FOLL_FORCE can write to even unwritable pte's, but only
 65  * after we've gone through a COW cycle and they are dirty.
 66  */
 67 static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
 68 {
 69         return pte_write(pte) ||
 70                 ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
 71 }
 72 
 73 static struct page *follow_page_pte(struct vm_area_struct *vma,
 74                 unsigned long address, pmd_t *pmd, unsigned int flags)
 75 {
 76         struct mm_struct *mm = vma->vm_mm;
 77         struct dev_pagemap *pgmap = NULL;
 78         struct page *page;
 79         spinlock_t *ptl;
 80         pte_t *ptep, pte;
 81 
 82 retry:
 83         if (unlikely(pmd_bad(*pmd)))
 84                 return no_page_table(vma, flags);
 85 
 86         ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
 87         pte = *ptep;
 88         if (!pte_present(pte)) {
 89                 swp_entry_t entry;
 90                 /*
 91                  * KSM's break_ksm() relies upon recognizing a ksm page
 92                  * even while it is being migrated, so for that case we
 93                  * need migration_entry_wait().
 94                  */
 95                 if (likely(!(flags & FOLL_MIGRATION)))
 96                         goto no_page;
 97                 if (pte_none(pte))
 98                         goto no_page;
 99                 entry = pte_to_swp_entry(pte);
100                 if (!is_migration_entry(entry))
101                         goto no_page;
102                 pte_unmap_unlock(ptep, ptl);
103                 migration_entry_wait(mm, pmd, address);
104                 goto retry;
105         }
106         if ((flags & FOLL_NUMA) && pte_protnone(pte))
107                 goto no_page;
108         if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags)) {
109                 pte_unmap_unlock(ptep, ptl);
110                 return NULL;
111         }
112 
113         page = vm_normal_page(vma, address, pte);
114         if (!page && pte_devmap(pte) && (flags & FOLL_GET)) {
115                 /*
116                  * Only return device mapping pages in the FOLL_GET case since
117                  * they are only valid while holding the pgmap reference.
118                  */
119                 pgmap = get_dev_pagemap(pte_pfn(pte), NULL);
120                 if (pgmap)
121                         page = pte_page(pte);
122                 else
123                         goto no_page;
124         } else if (unlikely(!page)) {
125                 if (flags & FOLL_DUMP) {
126                         /* Avoid special (like zero) pages in core dumps */
127                         page = ERR_PTR(-EFAULT);
128                         goto out;
129                 }
130 
131                 if (is_zero_pfn(pte_pfn(pte))) {
132                         page = pte_page(pte);
133                 } else {
134                         int ret;
135 
136                         ret = follow_pfn_pte(vma, address, ptep, flags);
137                         page = ERR_PTR(ret);
138                         goto out;
139                 }
140         }
141 
142         if (flags & FOLL_SPLIT && PageTransCompound(page)) {
143                 int ret;
144                 get_page(page);
145                 pte_unmap_unlock(ptep, ptl);
146                 lock_page(page);
147                 ret = split_huge_page(page);
148                 unlock_page(page);
149                 put_page(page);
150                 if (ret)
151                         return ERR_PTR(ret);
152                 goto retry;
153         }
154 
155         if (flags & FOLL_GET) {
156                 get_page(page);
157 
158                 /* drop the pgmap reference now that we hold the page */
159                 if (pgmap) {
160                         put_dev_pagemap(pgmap);
161                         pgmap = NULL;
162                 }
163         }
164         if (flags & FOLL_TOUCH) {
165                 if ((flags & FOLL_WRITE) &&
166                     !pte_dirty(pte) && !PageDirty(page))
167                         set_page_dirty(page);
168                 /*
169                  * pte_mkyoung() would be more correct here, but atomic care
170                  * is needed to avoid losing the dirty bit: it is easier to use
171                  * mark_page_accessed().
172                  */
173                 mark_page_accessed(page);
174         }
175         if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
176                 /* Do not mlock pte-mapped THP */
177                 if (PageTransCompound(page))
178                         goto out;
179 
180                 /*
181                  * The preliminary mapping check is mainly to avoid the
182                  * pointless overhead of lock_page on the ZERO_PAGE
183                  * which might bounce very badly if there is contention.
184                  *
185                  * If the page is already locked, we don't need to
186                  * handle it now - vmscan will handle it later if and
187                  * when it attempts to reclaim the page.
188                  */
189                 if (page->mapping && trylock_page(page)) {
190                         lru_add_drain();  /* push cached pages to LRU */
191                         /*
192                          * Because we lock page here, and migration is
193                          * blocked by the pte's page reference, and we
194                          * know the page is still mapped, we don't even
195                          * need to check for file-cache page truncation.
196                          */
197                         mlock_vma_page(page);
198                         unlock_page(page);
199                 }
200         }
201 out:
202         pte_unmap_unlock(ptep, ptl);
203         return page;
204 no_page:
205         pte_unmap_unlock(ptep, ptl);
206         if (!pte_none(pte))
207                 return NULL;
208         return no_page_table(vma, flags);
209 }
210 
211 /**
212  * follow_page_mask - look up a page descriptor from a user-virtual address
213  * @vma: vm_area_struct mapping @address
214  * @address: virtual address to look up
215  * @flags: flags modifying lookup behaviour
216  * @page_mask: on output, *page_mask is set according to the size of the page
217  *
218  * @flags can have FOLL_ flags set, defined in <linux/mm.h>
219  *
220  * Returns the mapped (struct page *), %NULL if no mapping exists, or
221  * an error pointer if there is a mapping to something not represented
222  * by a page descriptor (see also vm_normal_page()).
223  */
224 struct page *follow_page_mask(struct vm_area_struct *vma,
225                               unsigned long address, unsigned int flags,
226                               unsigned int *page_mask)
227 {
228         pgd_t *pgd;
229         pud_t *pud;
230         pmd_t *pmd;
231         spinlock_t *ptl;
232         struct page *page;
233         struct mm_struct *mm = vma->vm_mm;
234 
235         *page_mask = 0;
236 
237         page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
238         if (!IS_ERR(page)) {
239                 BUG_ON(flags & FOLL_GET);
240                 return page;
241         }
242 
243         pgd = pgd_offset(mm, address);
244         if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
245                 return no_page_table(vma, flags);
246 
247         pud = pud_offset(pgd, address);
248         if (pud_none(*pud))
249                 return no_page_table(vma, flags);
250         if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB) {
251                 page = follow_huge_pud(mm, address, pud, flags);
252                 if (page)
253                         return page;
254                 return no_page_table(vma, flags);
255         }
256         if (unlikely(pud_bad(*pud)))
257                 return no_page_table(vma, flags);
258 
259         pmd = pmd_offset(pud, address);
260         if (pmd_none(*pmd))
261                 return no_page_table(vma, flags);
262         if (pmd_huge(*pmd) && vma->vm_flags & VM_HUGETLB) {
263                 page = follow_huge_pmd(mm, address, pmd, flags);
264                 if (page)
265                         return page;
266                 return no_page_table(vma, flags);
267         }
268         if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
269                 return no_page_table(vma, flags);
270         if (pmd_devmap(*pmd)) {
271                 ptl = pmd_lock(mm, pmd);
272                 page = follow_devmap_pmd(vma, address, pmd, flags);
273                 spin_unlock(ptl);
274                 if (page)
275                         return page;
276         }
277         if (likely(!pmd_trans_huge(*pmd)))
278                 return follow_page_pte(vma, address, pmd, flags);
279 
280         ptl = pmd_lock(mm, pmd);
281         if (unlikely(!pmd_trans_huge(*pmd))) {
282                 spin_unlock(ptl);
283                 return follow_page_pte(vma, address, pmd, flags);
284         }
285         if (flags & FOLL_SPLIT) {
286                 int ret;
287                 page = pmd_page(*pmd);
288                 if (is_huge_zero_page(page)) {
289                         spin_unlock(ptl);
290                         ret = 0;
291                         split_huge_pmd(vma, pmd, address);
292                         if (pmd_trans_unstable(pmd))
293                                 ret = -EBUSY;
294                 } else {
295                         get_page(page);
296                         spin_unlock(ptl);
297                         lock_page(page);
298                         ret = split_huge_page(page);
299                         unlock_page(page);
300                         put_page(page);
301                         if (pmd_none(*pmd))
302                                 return no_page_table(vma, flags);
303                 }
304 
305                 return ret ? ERR_PTR(ret) :
306                         follow_page_pte(vma, address, pmd, flags);
307         }
308 
309         page = follow_trans_huge_pmd(vma, address, pmd, flags);
310         spin_unlock(ptl);
311         *page_mask = HPAGE_PMD_NR - 1;
312         return page;
313 }
314 
315 static int get_gate_page(struct mm_struct *mm, unsigned long address,
316                 unsigned int gup_flags, struct vm_area_struct **vma,
317                 struct page **page)
318 {
319         pgd_t *pgd;
320         pud_t *pud;
321         pmd_t *pmd;
322         pte_t *pte;
323         int ret = -EFAULT;
324 
325         /* user gate pages are read-only */
326         if (gup_flags & FOLL_WRITE)
327                 return -EFAULT;
328         if (address > TASK_SIZE)
329                 pgd = pgd_offset_k(address);
330         else
331                 pgd = pgd_offset_gate(mm, address);
332         BUG_ON(pgd_none(*pgd));
333         pud = pud_offset(pgd, address);
334         BUG_ON(pud_none(*pud));
335         pmd = pmd_offset(pud, address);
336         if (pmd_none(*pmd))
337                 return -EFAULT;
338         VM_BUG_ON(pmd_trans_huge(*pmd));
339         pte = pte_offset_map(pmd, address);
340         if (pte_none(*pte))
341                 goto unmap;
342         *vma = get_gate_vma(mm);
343         if (!page)
344                 goto out;
345         *page = vm_normal_page(*vma, address, *pte);
346         if (!*page) {
347                 if ((gup_flags & FOLL_DUMP) || !is_zero_pfn(pte_pfn(*pte)))
348                         goto unmap;
349                 *page = pte_page(*pte);
350         }
351         get_page(*page);
352 out:
353         ret = 0;
354 unmap:
355         pte_unmap(pte);
356         return ret;
357 }
358 
359 /*
360  * mmap_sem must be held on entry.  If @nonblocking != NULL and
361  * *@flags does not include FOLL_NOWAIT, the mmap_sem may be released.
362  * If it is, *@nonblocking will be set to 0 and -EBUSY returned.
363  */
364 static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
365                 unsigned long address, unsigned int *flags, int *nonblocking)
366 {
367         unsigned int fault_flags = 0;
368         int ret;
369 
370         /* mlock all present pages, but do not fault in new pages */
371         if ((*flags & (FOLL_POPULATE | FOLL_MLOCK)) == FOLL_MLOCK)
372                 return -ENOENT;
373         /* For mm_populate(), just skip the stack guard page. */
374         if ((*flags & FOLL_POPULATE) &&
375                         (stack_guard_page_start(vma, address) ||
376                          stack_guard_page_end(vma, address + PAGE_SIZE)))
377                 return -ENOENT;
378         if (*flags & FOLL_WRITE)
379                 fault_flags |= FAULT_FLAG_WRITE;
380         if (*flags & FOLL_REMOTE)
381                 fault_flags |= FAULT_FLAG_REMOTE;
382         if (nonblocking)
383                 fault_flags |= FAULT_FLAG_ALLOW_RETRY;
384         if (*flags & FOLL_NOWAIT)
385                 fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
386         if (*flags & FOLL_TRIED) {
387                 VM_WARN_ON_ONCE(fault_flags & FAULT_FLAG_ALLOW_RETRY);
388                 fault_flags |= FAULT_FLAG_TRIED;
389         }
390 
391         ret = handle_mm_fault(vma, address, fault_flags);
392         if (ret & VM_FAULT_ERROR) {
393                 if (ret & VM_FAULT_OOM)
394                         return -ENOMEM;
395                 if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))
396                         return *flags & FOLL_HWPOISON ? -EHWPOISON : -EFAULT;
397                 if (ret & (VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV))
398                         return -EFAULT;
399                 BUG();
400         }
401 
402         if (tsk) {
403                 if (ret & VM_FAULT_MAJOR)
404                         tsk->maj_flt++;
405                 else
406                         tsk->min_flt++;
407         }
408 
409         if (ret & VM_FAULT_RETRY) {
410                 if (nonblocking)
411                         *nonblocking = 0;
412                 return -EBUSY;
413         }
414 
415         /*
416          * The VM_FAULT_WRITE bit tells us that do_wp_page has broken COW when
417          * necessary, even if maybe_mkwrite decided not to set pte_write. We
418          * can thus safely do subsequent page lookups as if they were reads.
419          * But only do so when looping for pte_write is futile: in some cases
420          * userspace may also be wanting to write to the gotten user page,
421          * which a read fault here might prevent (a readonly page might get
422          * reCOWed by userspace write).
423          */
424         if ((ret & VM_FAULT_WRITE) && !(vma->vm_flags & VM_WRITE))
425                 *flags |= FOLL_COW;
426         return 0;
427 }
428 
429 static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
430 {
431         vm_flags_t vm_flags = vma->vm_flags;
432         int write = (gup_flags & FOLL_WRITE);
433         int foreign = (gup_flags & FOLL_REMOTE);
434 
435         if (vm_flags & (VM_IO | VM_PFNMAP))
436                 return -EFAULT;
437 
438         if (write) {
439                 if (!(vm_flags & VM_WRITE)) {
440                         if (!(gup_flags & FOLL_FORCE))
441                                 return -EFAULT;
442                         /*
443                          * We used to let the write,force case do COW in a
444                          * VM_MAYWRITE VM_SHARED !VM_WRITE vma, so ptrace could
445                          * set a breakpoint in a read-only mapping of an
446                          * executable, without corrupting the file (yet only
447                          * when that file had been opened for writing!).
448                          * Anon pages in shared mappings are surprising: now
449                          * just reject it.
450                          */
451                         if (!is_cow_mapping(vm_flags))
452                                 return -EFAULT;
453                 }
454         } else if (!(vm_flags & VM_READ)) {
455                 if (!(gup_flags & FOLL_FORCE))
456                         return -EFAULT;
457                 /*
458                  * Is there actually any vma we can reach here which does not
459                  * have VM_MAYREAD set?
460                  */
461                 if (!(vm_flags & VM_MAYREAD))
462                         return -EFAULT;
463         }
464         /*
465          * gups are always data accesses, not instruction
466          * fetches, so execute=false here
467          */
468         if (!arch_vma_access_permitted(vma, write, false, foreign))
469                 return -EFAULT;
470         return 0;
471 }
472 
473 /**
474  * __get_user_pages() - pin user pages in memory
475  * @tsk:        task_struct of target task
476  * @mm:         mm_struct of target mm
477  * @start:      starting user address
478  * @nr_pages:   number of pages from start to pin
479  * @gup_flags:  flags modifying pin behaviour
480  * @pages:      array that receives pointers to the pages pinned.
481  *              Should be at least nr_pages long. Or NULL, if caller
482  *              only intends to ensure the pages are faulted in.
483  * @vmas:       array of pointers to vmas corresponding to each page.
484  *              Or NULL if the caller does not require them.
485  * @nonblocking: whether waiting for disk IO or mmap_sem contention
486  *
487  * Returns number of pages pinned. This may be fewer than the number
488  * requested. If nr_pages is 0 or negative, returns 0. If no pages
489  * were pinned, returns -errno. Each page returned must be released
490  * with a put_page() call when it is finished with. vmas will only
491  * remain valid while mmap_sem is held.
492  *
493  * Must be called with mmap_sem held.  It may be released.  See below.
494  *
495  * __get_user_pages walks a process's page tables and takes a reference to
496  * each struct page that each user address corresponds to at a given
497  * instant. That is, it takes the page that would be accessed if a user
498  * thread accesses the given user virtual address at that instant.
499  *
500  * This does not guarantee that the page exists in the user mappings when
501  * __get_user_pages returns, and there may even be a completely different
502  * page there in some cases (eg. if mmapped pagecache has been invalidated
503  * and subsequently re faulted). However it does guarantee that the page
504  * won't be freed completely. And mostly callers simply care that the page
505  * contains data that was valid *at some point in time*. Typically, an IO
506  * or similar operation cannot guarantee anything stronger anyway because
507  * locks can't be held over the syscall boundary.
508  *
509  * If @gup_flags & FOLL_WRITE == 0, the page must not be written to. If
510  * the page is written to, set_page_dirty (or set_page_dirty_lock, as
511  * appropriate) must be called after the page is finished with, and
512  * before put_page is called.
513  *
514  * If @nonblocking != NULL, __get_user_pages will not wait for disk IO
515  * or mmap_sem contention, and if waiting is needed to pin all pages,
516  * *@nonblocking will be set to 0.  Further, if @gup_flags does not
517  * include FOLL_NOWAIT, the mmap_sem will be released via up_read() in
518  * this case.
519  *
520  * A caller using such a combination of @nonblocking and @gup_flags
521  * must therefore hold the mmap_sem for reading only, and recognize
522  * when it's been released.  Otherwise, it must be held for either
523  * reading or writing and will not be released.
524  *
525  * In most cases, get_user_pages or get_user_pages_fast should be used
526  * instead of __get_user_pages. __get_user_pages should be used only if
527  * you need some special @gup_flags.
528  */
529 static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
530                 unsigned long start, unsigned long nr_pages,
531                 unsigned int gup_flags, struct page **pages,
532                 struct vm_area_struct **vmas, int *nonblocking)
533 {
534         long i = 0;
535         unsigned int page_mask;
536         struct vm_area_struct *vma = NULL;
537 
538         if (!nr_pages)
539                 return 0;
540 
541         VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));
542 
543         /*
544          * If FOLL_FORCE is set then do not force a full fault as the hinting
545          * fault information is unrelated to the reference behaviour of a task
546          * using the address space
547          */
548         if (!(gup_flags & FOLL_FORCE))
549                 gup_flags |= FOLL_NUMA;
550 
551         do {
552                 struct page *page;
553                 unsigned int foll_flags = gup_flags;
554                 unsigned int page_increm;
555 
556                 /* first iteration or cross vma bound */
557                 if (!vma || start >= vma->vm_end) {
558                         vma = find_extend_vma(mm, start);
559                         if (!vma && in_gate_area(mm, start)) {
560                                 int ret;
561                                 ret = get_gate_page(mm, start & PAGE_MASK,
562                                                 gup_flags, &vma,
563                                                 pages ? &pages[i] : NULL);
564                                 if (ret)
565                                         return i ? : ret;
566                                 page_mask = 0;
567                                 goto next_page;
568                         }
569 
570                         if (!vma || check_vma_flags(vma, gup_flags))
571                                 return i ? : -EFAULT;
572                         if (is_vm_hugetlb_page(vma)) {
573                                 i = follow_hugetlb_page(mm, vma, pages, vmas,
574                                                 &start, &nr_pages, i,
575                                                 gup_flags);
576                                 continue;
577                         }
578                 }
579 retry:
580                 /*
581                  * If we have a pending SIGKILL, don't keep faulting pages and
582                  * potentially allocating memory.
583                  */
584                 if (unlikely(fatal_signal_pending(current)))
585                         return i ? i : -ERESTARTSYS;
586                 cond_resched();
587                 page = follow_page_mask(vma, start, foll_flags, &page_mask);
588                 if (!page) {
589                         int ret;
590                         ret = faultin_page(tsk, vma, start, &foll_flags,
591                                         nonblocking);
592                         switch (ret) {
593                         case 0:
594                                 goto retry;
595                         case -EFAULT:
596                         case -ENOMEM:
597                         case -EHWPOISON:
598                                 return i ? i : ret;
599                         case -EBUSY:
600                                 return i;
601                         case -ENOENT:
602                                 goto next_page;
603                         }
604                         BUG();
605                 } else if (PTR_ERR(page) == -EEXIST) {
606                         /*
607                          * Proper page table entry exists, but no corresponding
608                          * struct page.
609                          */
610                         goto next_page;
611                 } else if (IS_ERR(page)) {
612                         return i ? i : PTR_ERR(page);
613                 }
614                 if (pages) {
615                         pages[i] = page;
616                         flush_anon_page(vma, page, start);
617                         flush_dcache_page(page);
618                         page_mask = 0;
619                 }
620 next_page:
621                 if (vmas) {
622                         vmas[i] = vma;
623                         page_mask = 0;
624                 }
625                 page_increm = 1 + (~(start >> PAGE_SHIFT) & page_mask);
626                 if (page_increm > nr_pages)
627                         page_increm = nr_pages;
628                 i += page_increm;
629                 start += page_increm * PAGE_SIZE;
630                 nr_pages -= page_increm;
631         } while (nr_pages);
632         return i;
633 }
634 
635 static bool vma_permits_fault(struct vm_area_struct *vma,
636                               unsigned int fault_flags)
637 {
638         bool write   = !!(fault_flags & FAULT_FLAG_WRITE);
639         bool foreign = !!(fault_flags & FAULT_FLAG_REMOTE);
640         vm_flags_t vm_flags = write ? VM_WRITE : VM_READ;
641 
642         if (!(vm_flags & vma->vm_flags))
643                 return false;
644 
645         /*
646          * The architecture might have a hardware protection
647          * mechanism other than read/write that can deny access.
648          *
649          * gup always represents data access, not instruction
650          * fetches, so execute=false here:
651          */
652         if (!arch_vma_access_permitted(vma, write, false, foreign))
653                 return false;
654 
655         return true;
656 }
657 
658 /*
659  * fixup_user_fault() - manually resolve a user page fault
660  * @tsk:        the task_struct to use for page fault accounting, or
661  *              NULL if faults are not to be recorded.
662  * @mm:         mm_struct of target mm
663  * @address:    user address
664  * @fault_flags:flags to pass down to handle_mm_fault()
665  * @unlocked:   did we unlock the mmap_sem while retrying, maybe NULL if caller
666  *              does not allow retry
667  *
668  * This is meant to be called in the specific scenario where for locking reasons
669  * we try to access user memory in atomic context (within a pagefault_disable()
670  * section), this returns -EFAULT, and we want to resolve the user fault before
671  * trying again.
672  *
673  * Typically this is meant to be used by the futex code.
674  *
675  * The main difference with get_user_pages() is that this function will
676  * unconditionally call handle_mm_fault() which will in turn perform all the
677  * necessary SW fixup of the dirty and young bits in the PTE, while
678  * get_user_pages() only guarantees to update these in the struct page.
679  *
680  * This is important for some architectures where those bits also gate the
681  * access permission to the page because they are maintained in software.  On
682  * such architectures, gup() will not be enough to make a subsequent access
683  * succeed.
684  *
685  * This function will not return with an unlocked mmap_sem. So it has not the
686  * same semantics wrt the @mm->mmap_sem as does filemap_fault().
687  */
688 int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
689                      unsigned long address, unsigned int fault_flags,
690                      bool *unlocked)
691 {
692         struct vm_area_struct *vma;
693         int ret, major = 0;
694 
695         if (unlocked)
696                 fault_flags |= FAULT_FLAG_ALLOW_RETRY;
697 
698 retry:
699         vma = find_extend_vma(mm, address);
700         if (!vma || address < vma->vm_start)
701                 return -EFAULT;
702 
703         if (!vma_permits_fault(vma, fault_flags))
704                 return -EFAULT;
705 
706         ret = handle_mm_fault(vma, address, fault_flags);
707         major |= ret & VM_FAULT_MAJOR;
708         if (ret & VM_FAULT_ERROR) {
709                 if (ret & VM_FAULT_OOM)
710                         return -ENOMEM;
711                 if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))
712                         return -EHWPOISON;
713                 if (ret & (VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV))
714                         return -EFAULT;
715                 BUG();
716         }
717 
718         if (ret & VM_FAULT_RETRY) {
719                 down_read(&mm->mmap_sem);
720                 if (!(fault_flags & FAULT_FLAG_TRIED)) {
721                         *unlocked = true;
722                         fault_flags &= ~FAULT_FLAG_ALLOW_RETRY;
723                         fault_flags |= FAULT_FLAG_TRIED;
724                         goto retry;
725                 }
726         }
727 
728         if (tsk) {
729                 if (major)
730                         tsk->maj_flt++;
731                 else
732                         tsk->min_flt++;
733         }
734         return 0;
735 }
736 EXPORT_SYMBOL_GPL(fixup_user_fault);
737 
738 static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
739                                                 struct mm_struct *mm,
740                                                 unsigned long start,
741                                                 unsigned long nr_pages,
742                                                 struct page **pages,
743                                                 struct vm_area_struct **vmas,
744                                                 int *locked, bool notify_drop,
745                                                 unsigned int flags)
746 {
747         long ret, pages_done;
748         bool lock_dropped;
749 
750         if (locked) {
751                 /* if VM_FAULT_RETRY can be returned, vmas become invalid */
752                 BUG_ON(vmas);
753                 /* check caller initialized locked */
754                 BUG_ON(*locked != 1);
755         }
756 
757         if (pages)
758                 flags |= FOLL_GET;
759 
760         pages_done = 0;
761         lock_dropped = false;
762         for (;;) {
763                 ret = __get_user_pages(tsk, mm, start, nr_pages, flags, pages,
764                                        vmas, locked);
765                 if (!locked)
766                         /* VM_FAULT_RETRY couldn't trigger, bypass */
767                         return ret;
768 
769                 /* VM_FAULT_RETRY cannot return errors */
770                 if (!*locked) {
771                         BUG_ON(ret < 0);
772                         BUG_ON(ret >= nr_pages);
773                 }
774 
775                 if (!pages)
776                         /* If it's a prefault don't insist harder */
777                         return ret;
778 
779                 if (ret > 0) {
780                         nr_pages -= ret;
781                         pages_done += ret;
782                         if (!nr_pages)
783                                 break;
784                 }
785                 if (*locked) {
786                         /* VM_FAULT_RETRY didn't trigger */
787                         if (!pages_done)
788                                 pages_done = ret;
789                         break;
790                 }
791                 /* VM_FAULT_RETRY triggered, so seek to the faulting offset */
792                 pages += ret;
793                 start += ret << PAGE_SHIFT;
794 
795                 /*
796                  * Repeat on the address that fired VM_FAULT_RETRY
797                  * without FAULT_FLAG_ALLOW_RETRY but with
798                  * FAULT_FLAG_TRIED.
799                  */
800                 *locked = 1;
801                 lock_dropped = true;
802                 down_read(&mm->mmap_sem);
803                 ret = __get_user_pages(tsk, mm, start, 1, flags | FOLL_TRIED,
804                                        pages, NULL, NULL);
805                 if (ret != 1) {
806                         BUG_ON(ret > 1);
807                         if (!pages_done)
808                                 pages_done = ret;
809                         break;
810                 }
811                 nr_pages--;
812                 pages_done++;
813                 if (!nr_pages)
814                         break;
815                 pages++;
816                 start += PAGE_SIZE;
817         }
818         if (notify_drop && lock_dropped && *locked) {
819                 /*
820                  * We must let the caller know we temporarily dropped the lock
821                  * and so the critical section protected by it was lost.
822                  */
823                 up_read(&mm->mmap_sem);
824                 *locked = 0;
825         }
826         return pages_done;
827 }
828 
829 /*
830  * We can leverage the VM_FAULT_RETRY functionality in the page fault
831  * paths better by using either get_user_pages_locked() or
832  * get_user_pages_unlocked().
833  *
834  * get_user_pages_locked() is suitable to replace the form:
835  *
836  *      down_read(&mm->mmap_sem);
837  *      do_something()
838  *      get_user_pages(tsk, mm, ..., pages, NULL);
839  *      up_read(&mm->mmap_sem);
840  *
841  *  to:
842  *
843  *      int locked = 1;
844  *      down_read(&mm->mmap_sem);
845  *      do_something()
846  *      get_user_pages_locked(tsk, mm, ..., pages, &locked);
847  *      if (locked)
848  *          up_read(&mm->mmap_sem);
849  */
850 long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
851                            unsigned int gup_flags, struct page **pages,
852                            int *locked)
853 {
854         return __get_user_pages_locked(current, current->mm, start, nr_pages,
855                                        pages, NULL, locked, true,
856                                        gup_flags | FOLL_TOUCH);
857 }
858 EXPORT_SYMBOL(get_user_pages_locked);
859 
860 /*
861  * Same as get_user_pages_unlocked(...., FOLL_TOUCH) but it allows for
862  * tsk, mm to be specified.
863  *
864  * NOTE: here FOLL_TOUCH is not set implicitly and must be set by the
865  * caller if required (just like with __get_user_pages). "FOLL_GET"
866  * is set implicitly if "pages" is non-NULL.
867  */
868 static __always_inline long __get_user_pages_unlocked(struct task_struct *tsk,
869                 struct mm_struct *mm, unsigned long start,
870                 unsigned long nr_pages, struct page **pages,
871                 unsigned int gup_flags)
872 {
873         long ret;
874         int locked = 1;
875 
876         down_read(&mm->mmap_sem);
877         ret = __get_user_pages_locked(tsk, mm, start, nr_pages, pages, NULL,
878                                       &locked, false, gup_flags);
879         if (locked)
880                 up_read(&mm->mmap_sem);
881         return ret;
882 }
883 
884 /*
885  * get_user_pages_unlocked() is suitable to replace the form:
886  *
887  *      down_read(&mm->mmap_sem);
888  *      get_user_pages(tsk, mm, ..., pages, NULL);
889  *      up_read(&mm->mmap_sem);
890  *
891  *  with:
892  *
893  *      get_user_pages_unlocked(tsk, mm, ..., pages);
894  *
895  * It is functionally equivalent to get_user_pages_fast so
896  * get_user_pages_fast should be used instead if specific gup_flags
897  * (e.g. FOLL_FORCE) are not required.
898  */
899 long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
900                              struct page **pages, unsigned int gup_flags)
901 {
902         return __get_user_pages_unlocked(current, current->mm, start, nr_pages,
903                                          pages, gup_flags | FOLL_TOUCH);
904 }
905 EXPORT_SYMBOL(get_user_pages_unlocked);
906 
907 /*
908  * get_user_pages_remote() - pin user pages in memory
909  * @tsk:        the task_struct to use for page fault accounting, or
910  *              NULL if faults are not to be recorded.
911  * @mm:         mm_struct of target mm
912  * @start:      starting user address
913  * @nr_pages:   number of pages from start to pin
914  * @gup_flags:  flags modifying lookup behaviour
915  * @pages:      array that receives pointers to the pages pinned.
916  *              Should be at least nr_pages long. Or NULL, if caller
917  *              only intends to ensure the pages are faulted in.
918  * @vmas:       array of pointers to vmas corresponding to each page.
919  *              Or NULL if the caller does not require them.
920  * @locked:     pointer to lock flag indicating whether lock is held and
921  *              subsequently whether VM_FAULT_RETRY functionality can be
922  *              utilised. Lock must initially be held.
923  *
924  * Returns number of pages pinned. This may be fewer than the number
925  * requested. If nr_pages is 0 or negative, returns 0. If no pages
926  * were pinned, returns -errno. Each page returned must be released
927  * with a put_page() call when it is finished with. vmas will only
928  * remain valid while mmap_sem is held.
929  *
930  * Must be called with mmap_sem held for read or write.
931  *
932  * get_user_pages walks a process's page tables and takes a reference to
933  * each struct page that each user address corresponds to at a given
934  * instant. That is, it takes the page that would be accessed if a user
935  * thread accesses the given user virtual address at that instant.
936  *
937  * This does not guarantee that the page exists in the user mappings when
938  * get_user_pages returns, and there may even be a completely different
939  * page there in some cases (eg. if mmapped pagecache has been invalidated
940  * and subsequently re faulted). However it does guarantee that the page
941  * won't be freed completely. And mostly callers simply care that the page
942  * contains data that was valid *at some point in time*. Typically, an IO
943  * or similar operation cannot guarantee anything stronger anyway because
944  * locks can't be held over the syscall boundary.
945  *
946  * If gup_flags & FOLL_WRITE == 0, the page must not be written to. If the page
947  * is written to, set_page_dirty (or set_page_dirty_lock, as appropriate) must
948  * be called after the page is finished with, and before put_page is called.
949  *
950  * get_user_pages is typically used for fewer-copy IO operations, to get a
951  * handle on the memory by some means other than accesses via the user virtual
952  * addresses. The pages may be submitted for DMA to devices or accessed via
953  * their kernel linear mapping (via the kmap APIs). Care should be taken to
954  * use the correct cache flushing APIs.
955  *
956  * See also get_user_pages_fast, for performance critical applications.
957  *
958  * get_user_pages should be phased out in favor of
959  * get_user_pages_locked|unlocked or get_user_pages_fast. Nothing
960  * should use get_user_pages because it cannot pass
961  * FAULT_FLAG_ALLOW_RETRY to handle_mm_fault.
962  */
963 long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
964                 unsigned long start, unsigned long nr_pages,
965                 unsigned int gup_flags, struct page **pages,
966                 struct vm_area_struct **vmas, int *locked)
967 {
968         return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
969                                        locked, true,
970                                        gup_flags | FOLL_TOUCH | FOLL_REMOTE);
971 }
972 EXPORT_SYMBOL(get_user_pages_remote);
973 
974 /*
975  * This is the same as get_user_pages_remote(), just with a
976  * less-flexible calling convention where we assume that the task
977  * and mm being operated on are the current task's and don't allow
978  * passing of a locked parameter.  We also obviously don't pass
979  * FOLL_REMOTE in here.
980  */
981 long get_user_pages(unsigned long start, unsigned long nr_pages,
982                 unsigned int gup_flags, struct page **pages,
983                 struct vm_area_struct **vmas)
984 {
985         return __get_user_pages_locked(current, current->mm, start, nr_pages,
986                                        pages, vmas, NULL, false,
987                                        gup_flags | FOLL_TOUCH);
988 }
989 EXPORT_SYMBOL(get_user_pages);
990 
991 /**
992  * populate_vma_page_range() -  populate a range of pages in the vma.
993  * @vma:   target vma
994  * @start: start address
995  * @end:   end address
996  * @nonblocking:
997  *
998  * This takes care of mlocking the pages too if VM_LOCKED is set.
999  *
1000  * return 0 on success, negative error code on error.
1001  *
1002  * vma->vm_mm->mmap_sem must be held.
1003  *
1004  * If @nonblocking is NULL, it may be held for read or write and will
1005  * be unperturbed.
1006  *
1007  * If @nonblocking is non-NULL, it must held for read only and may be
1008  * released.  If it's released, *@nonblocking will be set to 0.
1009  */
1010 long populate_vma_page_range(struct vm_area_struct *vma,
1011                 unsigned long start, unsigned long end, int *nonblocking)
1012 {
1013         struct mm_struct *mm = vma->vm_mm;
1014         unsigned long nr_pages = (end - start) / PAGE_SIZE;
1015         int gup_flags;
1016 
1017         VM_BUG_ON(start & ~PAGE_MASK);
1018         VM_BUG_ON(end   & ~PAGE_MASK);
1019         VM_BUG_ON_VMA(start < vma->vm_start, vma);
1020         VM_BUG_ON_VMA(end   > vma->vm_end, vma);
1021         VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm);
1022 
1023         gup_flags = FOLL_TOUCH | FOLL_POPULATE | FOLL_MLOCK;
1024         if (vma->vm_flags & VM_LOCKONFAULT)
1025                 gup_flags &= ~FOLL_POPULATE;
1026         /*
1027          * We want to touch writable mappings with a write fault in order
1028          * to break COW, except for shared mappings because these don't COW
1029          * and we would not want to dirty them for nothing.
1030          */
1031         if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
1032                 gup_flags |= FOLL_WRITE;
1033 
1034         /*
1035          * We want mlock to succeed for regions that have any permissions
1036          * other than PROT_NONE.
1037          */
1038         if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC))
1039                 gup_flags |= FOLL_FORCE;
1040 
1041         /*
1042          * We made sure addr is within a VMA, so the following will
1043          * not result in a stack expansion that recurses back here.
1044          */
1045         return __get_user_pages(current, mm, start, nr_pages, gup_flags,
1046                                 NULL, NULL, nonblocking);
1047 }
1048 
1049 /*
1050  * __mm_populate - populate and/or mlock pages within a range of address space.
1051  *
1052  * This is used to implement mlock() and the MAP_POPULATE / MAP_LOCKED mmap
1053  * flags. VMAs must be already marked with the desired vm_flags, and
1054  * mmap_sem must not be held.
1055  */
1056 int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
1057 {
1058         struct mm_struct *mm = current->mm;
1059         unsigned long end, nstart, nend;
1060         struct vm_area_struct *vma = NULL;
1061         int locked = 0;
1062         long ret = 0;
1063 
1064         VM_BUG_ON(start & ~PAGE_MASK);
1065         VM_BUG_ON(len != PAGE_ALIGN(len));
1066         end = start + len;
1067 
1068         for (nstart = start; nstart < end; nstart = nend) {
1069                 /*
1070                  * We want to fault in pages for [nstart; end) address range.
1071                  * Find first corresponding VMA.
1072                  */
1073                 if (!locked) {
1074                         locked = 1;
1075                         down_read(&mm->mmap_sem);
1076                         vma = find_vma(mm, nstart);
1077                 } else if (nstart >= vma->vm_end)
1078                         vma = vma->vm_next;
1079                 if (!vma || vma->vm_start >= end)
1080                         break;
1081                 /*
1082                  * Set [nstart; nend) to intersection of desired address
1083                  * range with the first VMA. Also, skip undesirable VMA types.
1084                  */
1085                 nend = min(end, vma->vm_end);
1086                 if (vma->vm_flags & (VM_IO | VM_PFNMAP))
1087                         continue;
1088                 if (nstart < vma->vm_start)
1089                         nstart = vma->vm_start;
1090                 /*
1091                  * Now fault in a range of pages. populate_vma_page_range()
1092                  * double checks the vma flags, so that it won't mlock pages
1093                  * if the vma was already munlocked.
1094                  */
1095                 ret = populate_vma_page_range(vma, nstart, nend, &locked);
1096                 if (ret < 0) {
1097                         if (ignore_errors) {
1098                                 ret = 0;
1099                                 continue;       /* continue at next VMA */
1100                         }
1101                         break;
1102                 }
1103                 nend = nstart + ret * PAGE_SIZE;
1104                 ret = 0;
1105         }
1106         if (locked)
1107                 up_read(&mm->mmap_sem);
1108         return ret;     /* 0 or negative error code */
1109 }
1110 
1111 /**
1112  * get_dump_page() - pin user page in memory while writing it to core dump
1113  * @addr: user address
1114  *
1115  * Returns struct page pointer of user page pinned for dump,
1116  * to be freed afterwards by put_page().
1117  *
1118  * Returns NULL on any kind of failure - a hole must then be inserted into
1119  * the corefile, to preserve alignment with its headers; and also returns
1120  * NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
1121  * allowing a hole to be left in the corefile to save diskspace.
1122  *
1123  * Called without mmap_sem, but after all other threads have been killed.
1124  */
1125 #ifdef CONFIG_ELF_CORE
1126 struct page *get_dump_page(unsigned long addr)
1127 {
1128         struct vm_area_struct *vma;
1129         struct page *page;
1130 
1131         if (__get_user_pages(current, current->mm, addr, 1,
1132                              FOLL_FORCE | FOLL_DUMP | FOLL_GET, &page, &vma,
1133                              NULL) < 1)
1134                 return NULL;
1135         flush_cache_page(vma, addr, page_to_pfn(page));
1136         return page;
1137 }
1138 #endif /* CONFIG_ELF_CORE */
1139 
1140 /*
1141  * Generic RCU Fast GUP
1142  *
1143  * get_user_pages_fast attempts to pin user pages by walking the page
1144  * tables directly and avoids taking locks. Thus the walker needs to be
1145  * protected from page table pages being freed from under it, and should
1146  * block any THP splits.
1147  *
1148  * One way to achieve this is to have the walker disable interrupts, and
1149  * rely on IPIs from the TLB flushing code blocking before the page table
1150  * pages are freed. This is unsuitable for architectures that do not need
1151  * to broadcast an IPI when invalidating TLBs.
1152  *
1153  * Another way to achieve this is to batch up page table containing pages
1154  * belonging to more than one mm_user, then rcu_sched a callback to free those
1155  * pages. Disabling interrupts will allow the fast_gup walker to both block
1156  * the rcu_sched callback, and an IPI that we broadcast for splitting THPs
1157  * (which is a relatively rare event). The code below adopts this strategy.
1158  *
1159  * Before activating this code, please be aware that the following assumptions
1160  * are currently made:
1161  *
1162  *  *) HAVE_RCU_TABLE_FREE is enabled, and tlb_remove_table is used to free
1163  *      pages containing page tables.
1164  *
1165  *  *) ptes can be read atomically by the architecture.
1166  *
1167  *  *) access_ok is sufficient to validate userspace address ranges.
1168  *
1169  * The last two assumptions can be relaxed by the addition of helper functions.
1170  *
1171  * This code is based heavily on the PowerPC implementation by Nick Piggin.
1172  */
1173 #ifdef CONFIG_HAVE_GENERIC_RCU_GUP
1174 
1175 #ifdef __HAVE_ARCH_PTE_SPECIAL
1176 static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
1177                          int write, struct page **pages, int *nr)
1178 {
1179         pte_t *ptep, *ptem;
1180         int ret = 0;
1181 
1182         ptem = ptep = pte_offset_map(&pmd, addr);
1183         do {
1184                 /*
1185                  * In the line below we are assuming that the pte can be read
1186                  * atomically. If this is not the case for your architecture,
1187                  * please wrap this in a helper function!
1188                  *
1189                  * for an example see gup_get_pte in arch/x86/mm/gup.c
1190                  */
1191                 pte_t pte = READ_ONCE(*ptep);
1192                 struct page *head, *page;
1193 
1194                 /*
1195                  * Similar to the PMD case below, NUMA hinting must take slow
1196                  * path using the pte_protnone check.
1197                  */
1198                 if (!pte_present(pte) || pte_special(pte) ||
1199                         pte_protnone(pte) || (write && !pte_write(pte)))
1200                         goto pte_unmap;
1201 
1202                 if (!arch_pte_access_permitted(pte, write))
1203                         goto pte_unmap;
1204 
1205                 VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
1206                 page = pte_page(pte);
1207                 head = compound_head(page);
1208 
1209                 if (!page_cache_get_speculative(head))
1210                         goto pte_unmap;
1211 
1212                 if (unlikely(pte_val(pte) != pte_val(*ptep))) {
1213                         put_page(head);
1214                         goto pte_unmap;
1215                 }
1216 
1217                 VM_BUG_ON_PAGE(compound_head(page) != head, page);
1218                 pages[*nr] = page;
1219                 (*nr)++;
1220 
1221         } while (ptep++, addr += PAGE_SIZE, addr != end);
1222 
1223         ret = 1;
1224 
1225 pte_unmap:
1226         pte_unmap(ptem);
1227         return ret;
1228 }
1229 #else
1230 
1231 /*
1232  * If we can't determine whether or not a pte is special, then fail immediately
1233  * for ptes. Note, we can still pin HugeTLB and THP as these are guaranteed not
1234  * to be special.
1235  *
1236  * For a futex to be placed on a THP tail page, get_futex_key requires a
1237  * __get_user_pages_fast implementation that can pin pages. Thus it's still
1238  * useful to have gup_huge_pmd even if we can't operate on ptes.
1239  */
1240 static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
1241                          int write, struct page **pages, int *nr)
1242 {
1243         return 0;
1244 }
1245 #endif /* __HAVE_ARCH_PTE_SPECIAL */
1246 
1247 static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
1248                 unsigned long end, int write, struct page **pages, int *nr)
1249 {
1250         struct page *head, *page;
1251         int refs;
1252 
1253         if (write && !pmd_write(orig))
1254                 return 0;
1255 
1256         refs = 0;
1257         head = pmd_page(orig);
1258         page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
1259         do {
1260                 VM_BUG_ON_PAGE(compound_head(page) != head, page);
1261                 pages[*nr] = page;
1262                 (*nr)++;
1263                 page++;
1264                 refs++;
1265         } while (addr += PAGE_SIZE, addr != end);
1266 
1267         if (!page_cache_add_speculative(head, refs)) {
1268                 *nr -= refs;
1269                 return 0;
1270         }
1271 
1272         if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
1273                 *nr -= refs;
1274                 while (refs--)
1275                         put_page(head);
1276                 return 0;
1277         }
1278 
1279         return 1;
1280 }
1281 
1282 static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
1283                 unsigned long end, int write, struct page **pages, int *nr)
1284 {
1285         struct page *head, *page;
1286         int refs;
1287 
1288         if (write && !pud_write(orig))
1289                 return 0;
1290 
1291         refs = 0;
1292         head = pud_page(orig);
1293         page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
1294         do {
1295                 VM_BUG_ON_PAGE(compound_head(page) != head, page);
1296                 pages[*nr] = page;
1297                 (*nr)++;
1298                 page++;
1299                 refs++;
1300         } while (addr += PAGE_SIZE, addr != end);
1301 
1302         if (!page_cache_add_speculative(head, refs)) {
1303                 *nr -= refs;
1304                 return 0;
1305         }
1306 
1307         if (unlikely(pud_val(orig) != pud_val(*pudp))) {
1308                 *nr -= refs;
1309                 while (refs--)
1310                         put_page(head);
1311                 return 0;
1312         }
1313 
1314         return 1;
1315 }
1316 
1317 static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
1318                         unsigned long end, int write,
1319                         struct page **pages, int *nr)
1320 {
1321         int refs;
1322         struct page *head, *page;
1323 
1324         if (write && !pgd_write(orig))
1325                 return 0;
1326 
1327         refs = 0;
1328         head = pgd_page(orig);
1329         page = head + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
1330         do {
1331                 VM_BUG_ON_PAGE(compound_head(page) != head, page);
1332                 pages[*nr] = page;
1333                 (*nr)++;
1334                 page++;
1335                 refs++;
1336         } while (addr += PAGE_SIZE, addr != end);
1337 
1338         if (!page_cache_add_speculative(head, refs)) {
1339                 *nr -= refs;
1340                 return 0;
1341         }
1342 
1343         if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) {
1344                 *nr -= refs;
1345                 while (refs--)
1346                         put_page(head);
1347                 return 0;
1348         }
1349 
1350         return 1;
1351 }
1352 
1353 static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
1354                 int write, struct page **pages, int *nr)
1355 {
1356         unsigned long next;
1357         pmd_t *pmdp;
1358 
1359         pmdp = pmd_offset(&pud, addr);
1360         do {
1361                 pmd_t pmd = READ_ONCE(*pmdp);
1362 
1363                 next = pmd_addr_end(addr, end);
1364                 if (pmd_none(pmd))
1365                         return 0;
1366 
1367                 if (unlikely(pmd_trans_huge(pmd) || pmd_huge(pmd))) {
1368                         /*
1369                          * NUMA hinting faults need to be handled in the GUP
1370                          * slowpath for accounting purposes and so that they
1371                          * can be serialised against THP migration.
1372                          */
1373                         if (pmd_protnone(pmd))
1374                                 return 0;
1375 
1376                         if (!gup_huge_pmd(pmd, pmdp, addr, next, write,
1377                                 pages, nr))
1378                                 return 0;
1379 
1380                 } else if (unlikely(is_hugepd(__hugepd(pmd_val(pmd))))) {
1381                         /*
1382                          * architecture have different format for hugetlbfs
1383                          * pmd format and THP pmd format
1384                          */
1385                         if (!gup_huge_pd(__hugepd(pmd_val(pmd)), addr,
1386                                          PMD_SHIFT, next, write, pages, nr))
1387                                 return 0;
1388                 } else if (!gup_pte_range(pmd, addr, next, write, pages, nr))
1389                                 return 0;
1390         } while (pmdp++, addr = next, addr != end);
1391 
1392         return 1;
1393 }
1394 
1395 static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
1396                          int write, struct page **pages, int *nr)
1397 {
1398         unsigned long next;
1399         pud_t *pudp;
1400 
1401         pudp = pud_offset(&pgd, addr);
1402         do {
1403                 pud_t pud = READ_ONCE(*pudp);
1404 
1405                 next = pud_addr_end(addr, end);
1406                 if (pud_none(pud))
1407                         return 0;
1408                 if (unlikely(pud_huge(pud))) {
1409                         if (!gup_huge_pud(pud, pudp, addr, next, write,
1410                                           pages, nr))
1411                                 return 0;
1412                 } else if (unlikely(is_hugepd(__hugepd(pud_val(pud))))) {
1413                         if (!gup_huge_pd(__hugepd(pud_val(pud)), addr,
1414                                          PUD_SHIFT, next, write, pages, nr))
1415                                 return 0;
1416                 } else if (!gup_pmd_range(pud, addr, next, write, pages, nr))
1417                         return 0;
1418         } while (pudp++, addr = next, addr != end);
1419 
1420         return 1;
1421 }
1422 
1423 /*
1424  * Like get_user_pages_fast() except it's IRQ-safe in that it won't fall back to
1425  * the regular GUP. It will only return non-negative values.
1426  */
1427 int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
1428                           struct page **pages)
1429 {
1430         struct mm_struct *mm = current->mm;
1431         unsigned long addr, len, end;
1432         unsigned long next, flags;
1433         pgd_t *pgdp;
1434         int nr = 0;
1435 
1436         start &= PAGE_MASK;
1437         addr = start;
1438         len = (unsigned long) nr_pages << PAGE_SHIFT;
1439         end = start + len;
1440 
1441         if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
1442                                         start, len)))
1443                 return 0;
1444 
1445         /*
1446          * Disable interrupts.  We use the nested form as we can already have
1447          * interrupts disabled by get_futex_key.
1448          *
1449          * With interrupts disabled, we block page table pages from being
1450          * freed from under us. See mmu_gather_tlb in asm-generic/tlb.h
1451          * for more details.
1452          *
1453          * We do not adopt an rcu_read_lock(.) here as we also want to
1454          * block IPIs that come from THPs splitting.
1455          */
1456 
1457         local_irq_save(flags);
1458         pgdp = pgd_offset(mm, addr);
1459         do {
1460                 pgd_t pgd = READ_ONCE(*pgdp);
1461 
1462                 next = pgd_addr_end(addr, end);
1463                 if (pgd_none(pgd))
1464                         break;
1465                 if (unlikely(pgd_huge(pgd))) {
1466                         if (!gup_huge_pgd(pgd, pgdp, addr, next, write,
1467                                           pages, &nr))
1468                                 break;
1469                 } else if (unlikely(is_hugepd(__hugepd(pgd_val(pgd))))) {
1470                         if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr,
1471                                          PGDIR_SHIFT, next, write, pages, &nr))
1472                                 break;
1473                 } else if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
1474                         break;
1475         } while (pgdp++, addr = next, addr != end);
1476         local_irq_restore(flags);
1477 
1478         return nr;
1479 }
1480 
1481 /**
1482  * get_user_pages_fast() - pin user pages in memory
1483  * @start:      starting user address
1484  * @nr_pages:   number of pages from start to pin
1485  * @write:      whether pages will be written to
1486  * @pages:      array that receives pointers to the pages pinned.
1487  *              Should be at least nr_pages long.
1488  *
1489  * Attempt to pin user pages in memory without taking mm->mmap_sem.
1490  * If not successful, it will fall back to taking the lock and
1491  * calling get_user_pages().
1492  *
1493  * Returns number of pages pinned. This may be fewer than the number
1494  * requested. If nr_pages is 0 or negative, returns 0. If no pages
1495  * were pinned, returns -errno.
1496  */
1497 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
1498                         struct page **pages)
1499 {
1500         int nr, ret;
1501 
1502         start &= PAGE_MASK;
1503         nr = __get_user_pages_fast(start, nr_pages, write, pages);
1504         ret = nr;
1505 
1506         if (nr < nr_pages) {
1507                 /* Try to get the remaining pages with get_user_pages */
1508                 start += nr << PAGE_SHIFT;
1509                 pages += nr;
1510 
1511                 ret = get_user_pages_unlocked(start, nr_pages - nr, pages,
1512                                 write ? FOLL_WRITE : 0);
1513 
1514                 /* Have to be a bit careful with return values */
1515                 if (nr > 0) {
1516                         if (ret < 0)
1517                                 ret = nr;
1518                         else
1519                                 ret += nr;
1520                 }
1521         }
1522 
1523         return ret;
1524 }
1525 
1526 #endif /* CONFIG_HAVE_GENERIC_RCU_GUP */
1527 

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