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Linux/mm/mlock.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*
  3  *      linux/mm/mlock.c
  4  *
  5  *  (C) Copyright 1995 Linus Torvalds
  6  *  (C) Copyright 2002 Christoph Hellwig
  7  */
  8 
  9 #include <linux/capability.h>
 10 #include <linux/mman.h>
 11 #include <linux/mm.h>
 12 #include <linux/sched/user.h>
 13 #include <linux/swap.h>
 14 #include <linux/swapops.h>
 15 #include <linux/pagemap.h>
 16 #include <linux/pagevec.h>
 17 #include <linux/mempolicy.h>
 18 #include <linux/syscalls.h>
 19 #include <linux/sched.h>
 20 #include <linux/export.h>
 21 #include <linux/rmap.h>
 22 #include <linux/mmzone.h>
 23 #include <linux/hugetlb.h>
 24 #include <linux/memcontrol.h>
 25 #include <linux/mm_inline.h>
 26 
 27 #include "internal.h"
 28 
 29 bool can_do_mlock(void)
 30 {
 31         if (rlimit(RLIMIT_MEMLOCK) != 0)
 32                 return true;
 33         if (capable(CAP_IPC_LOCK))
 34                 return true;
 35         return false;
 36 }
 37 EXPORT_SYMBOL(can_do_mlock);
 38 
 39 /*
 40  * Mlocked pages are marked with PageMlocked() flag for efficient testing
 41  * in vmscan and, possibly, the fault path; and to support semi-accurate
 42  * statistics.
 43  *
 44  * An mlocked page [PageMlocked(page)] is unevictable.  As such, it will
 45  * be placed on the LRU "unevictable" list, rather than the [in]active lists.
 46  * The unevictable list is an LRU sibling list to the [in]active lists.
 47  * PageUnevictable is set to indicate the unevictable state.
 48  *
 49  * When lazy mlocking via vmscan, it is important to ensure that the
 50  * vma's VM_LOCKED status is not concurrently being modified, otherwise we
 51  * may have mlocked a page that is being munlocked. So lazy mlock must take
 52  * the mmap_lock for read, and verify that the vma really is locked
 53  * (see mm/rmap.c).
 54  */
 55 
 56 /*
 57  *  LRU accounting for clear_page_mlock()
 58  */
 59 void clear_page_mlock(struct page *page)
 60 {
 61         int nr_pages;
 62 
 63         if (!TestClearPageMlocked(page))
 64                 return;
 65 
 66         nr_pages = thp_nr_pages(page);
 67         mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages);
 68         count_vm_events(UNEVICTABLE_PGCLEARED, nr_pages);
 69         /*
 70          * The previous TestClearPageMlocked() corresponds to the smp_mb()
 71          * in __pagevec_lru_add_fn().
 72          *
 73          * See __pagevec_lru_add_fn for more explanation.
 74          */
 75         if (!isolate_lru_page(page)) {
 76                 putback_lru_page(page);
 77         } else {
 78                 /*
 79                  * We lost the race. the page already moved to evictable list.
 80                  */
 81                 if (PageUnevictable(page))
 82                         count_vm_events(UNEVICTABLE_PGSTRANDED, nr_pages);
 83         }
 84 }
 85 
 86 /*
 87  * Mark page as mlocked if not already.
 88  * If page on LRU, isolate and putback to move to unevictable list.
 89  */
 90 void mlock_vma_page(struct page *page)
 91 {
 92         /* Serialize with page migration */
 93         BUG_ON(!PageLocked(page));
 94 
 95         VM_BUG_ON_PAGE(PageTail(page), page);
 96         VM_BUG_ON_PAGE(PageCompound(page) && PageDoubleMap(page), page);
 97 
 98         if (!TestSetPageMlocked(page)) {
 99                 int nr_pages = thp_nr_pages(page);
100 
101                 mod_zone_page_state(page_zone(page), NR_MLOCK, nr_pages);
102                 count_vm_events(UNEVICTABLE_PGMLOCKED, nr_pages);
103                 if (!isolate_lru_page(page))
104                         putback_lru_page(page);
105         }
106 }
107 
108 /*
109  * Isolate a page from LRU with optional get_page() pin.
110  * Assumes lru_lock already held and page already pinned.
111  */
112 static bool __munlock_isolate_lru_page(struct page *page, bool getpage)
113 {
114         if (PageLRU(page)) {
115                 struct lruvec *lruvec;
116 
117                 lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page));
118                 if (getpage)
119                         get_page(page);
120                 ClearPageLRU(page);
121                 del_page_from_lru_list(page, lruvec, page_lru(page));
122                 return true;
123         }
124 
125         return false;
126 }
127 
128 /*
129  * Finish munlock after successful page isolation
130  *
131  * Page must be locked. This is a wrapper for try_to_munlock()
132  * and putback_lru_page() with munlock accounting.
133  */
134 static void __munlock_isolated_page(struct page *page)
135 {
136         /*
137          * Optimization: if the page was mapped just once, that's our mapping
138          * and we don't need to check all the other vmas.
139          */
140         if (page_mapcount(page) > 1)
141                 try_to_munlock(page);
142 
143         /* Did try_to_unlock() succeed or punt? */
144         if (!PageMlocked(page))
145                 count_vm_events(UNEVICTABLE_PGMUNLOCKED, thp_nr_pages(page));
146 
147         putback_lru_page(page);
148 }
149 
150 /*
151  * Accounting for page isolation fail during munlock
152  *
153  * Performs accounting when page isolation fails in munlock. There is nothing
154  * else to do because it means some other task has already removed the page
155  * from the LRU. putback_lru_page() will take care of removing the page from
156  * the unevictable list, if necessary. vmscan [page_referenced()] will move
157  * the page back to the unevictable list if some other vma has it mlocked.
158  */
159 static void __munlock_isolation_failed(struct page *page)
160 {
161         int nr_pages = thp_nr_pages(page);
162 
163         if (PageUnevictable(page))
164                 __count_vm_events(UNEVICTABLE_PGSTRANDED, nr_pages);
165         else
166                 __count_vm_events(UNEVICTABLE_PGMUNLOCKED, nr_pages);
167 }
168 
169 /**
170  * munlock_vma_page - munlock a vma page
171  * @page: page to be unlocked, either a normal page or THP page head
172  *
173  * returns the size of the page as a page mask (0 for normal page,
174  *         HPAGE_PMD_NR - 1 for THP head page)
175  *
176  * called from munlock()/munmap() path with page supposedly on the LRU.
177  * When we munlock a page, because the vma where we found the page is being
178  * munlock()ed or munmap()ed, we want to check whether other vmas hold the
179  * page locked so that we can leave it on the unevictable lru list and not
180  * bother vmscan with it.  However, to walk the page's rmap list in
181  * try_to_munlock() we must isolate the page from the LRU.  If some other
182  * task has removed the page from the LRU, we won't be able to do that.
183  * So we clear the PageMlocked as we might not get another chance.  If we
184  * can't isolate the page, we leave it for putback_lru_page() and vmscan
185  * [page_referenced()/try_to_unmap()] to deal with.
186  */
187 unsigned int munlock_vma_page(struct page *page)
188 {
189         int nr_pages;
190         pg_data_t *pgdat = page_pgdat(page);
191 
192         /* For try_to_munlock() and to serialize with page migration */
193         BUG_ON(!PageLocked(page));
194 
195         VM_BUG_ON_PAGE(PageTail(page), page);
196 
197         /*
198          * Serialize with any parallel __split_huge_page_refcount() which
199          * might otherwise copy PageMlocked to part of the tail pages before
200          * we clear it in the head page. It also stabilizes thp_nr_pages().
201          */
202         spin_lock_irq(&pgdat->lru_lock);
203 
204         if (!TestClearPageMlocked(page)) {
205                 /* Potentially, PTE-mapped THP: do not skip the rest PTEs */
206                 nr_pages = 1;
207                 goto unlock_out;
208         }
209 
210         nr_pages = thp_nr_pages(page);
211         __mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages);
212 
213         if (__munlock_isolate_lru_page(page, true)) {
214                 spin_unlock_irq(&pgdat->lru_lock);
215                 __munlock_isolated_page(page);
216                 goto out;
217         }
218         __munlock_isolation_failed(page);
219 
220 unlock_out:
221         spin_unlock_irq(&pgdat->lru_lock);
222 
223 out:
224         return nr_pages - 1;
225 }
226 
227 /*
228  * convert get_user_pages() return value to posix mlock() error
229  */
230 static int __mlock_posix_error_return(long retval)
231 {
232         if (retval == -EFAULT)
233                 retval = -ENOMEM;
234         else if (retval == -ENOMEM)
235                 retval = -EAGAIN;
236         return retval;
237 }
238 
239 /*
240  * Prepare page for fast batched LRU putback via putback_lru_evictable_pagevec()
241  *
242  * The fast path is available only for evictable pages with single mapping.
243  * Then we can bypass the per-cpu pvec and get better performance.
244  * when mapcount > 1 we need try_to_munlock() which can fail.
245  * when !page_evictable(), we need the full redo logic of putback_lru_page to
246  * avoid leaving evictable page in unevictable list.
247  *
248  * In case of success, @page is added to @pvec and @pgrescued is incremented
249  * in case that the page was previously unevictable. @page is also unlocked.
250  */
251 static bool __putback_lru_fast_prepare(struct page *page, struct pagevec *pvec,
252                 int *pgrescued)
253 {
254         VM_BUG_ON_PAGE(PageLRU(page), page);
255         VM_BUG_ON_PAGE(!PageLocked(page), page);
256 
257         if (page_mapcount(page) <= 1 && page_evictable(page)) {
258                 pagevec_add(pvec, page);
259                 if (TestClearPageUnevictable(page))
260                         (*pgrescued)++;
261                 unlock_page(page);
262                 return true;
263         }
264 
265         return false;
266 }
267 
268 /*
269  * Putback multiple evictable pages to the LRU
270  *
271  * Batched putback of evictable pages that bypasses the per-cpu pvec. Some of
272  * the pages might have meanwhile become unevictable but that is OK.
273  */
274 static void __putback_lru_fast(struct pagevec *pvec, int pgrescued)
275 {
276         count_vm_events(UNEVICTABLE_PGMUNLOCKED, pagevec_count(pvec));
277         /*
278          *__pagevec_lru_add() calls release_pages() so we don't call
279          * put_page() explicitly
280          */
281         __pagevec_lru_add(pvec);
282         count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
283 }
284 
285 /*
286  * Munlock a batch of pages from the same zone
287  *
288  * The work is split to two main phases. First phase clears the Mlocked flag
289  * and attempts to isolate the pages, all under a single zone lru lock.
290  * The second phase finishes the munlock only for pages where isolation
291  * succeeded.
292  *
293  * Note that the pagevec may be modified during the process.
294  */
295 static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
296 {
297         int i;
298         int nr = pagevec_count(pvec);
299         int delta_munlocked = -nr;
300         struct pagevec pvec_putback;
301         int pgrescued = 0;
302 
303         pagevec_init(&pvec_putback);
304 
305         /* Phase 1: page isolation */
306         spin_lock_irq(&zone->zone_pgdat->lru_lock);
307         for (i = 0; i < nr; i++) {
308                 struct page *page = pvec->pages[i];
309 
310                 if (TestClearPageMlocked(page)) {
311                         /*
312                          * We already have pin from follow_page_mask()
313                          * so we can spare the get_page() here.
314                          */
315                         if (__munlock_isolate_lru_page(page, false))
316                                 continue;
317                         else
318                                 __munlock_isolation_failed(page);
319                 } else {
320                         delta_munlocked++;
321                 }
322 
323                 /*
324                  * We won't be munlocking this page in the next phase
325                  * but we still need to release the follow_page_mask()
326                  * pin. We cannot do it under lru_lock however. If it's
327                  * the last pin, __page_cache_release() would deadlock.
328                  */
329                 pagevec_add(&pvec_putback, pvec->pages[i]);
330                 pvec->pages[i] = NULL;
331         }
332         __mod_zone_page_state(zone, NR_MLOCK, delta_munlocked);
333         spin_unlock_irq(&zone->zone_pgdat->lru_lock);
334 
335         /* Now we can release pins of pages that we are not munlocking */
336         pagevec_release(&pvec_putback);
337 
338         /* Phase 2: page munlock */
339         for (i = 0; i < nr; i++) {
340                 struct page *page = pvec->pages[i];
341 
342                 if (page) {
343                         lock_page(page);
344                         if (!__putback_lru_fast_prepare(page, &pvec_putback,
345                                         &pgrescued)) {
346                                 /*
347                                  * Slow path. We don't want to lose the last
348                                  * pin before unlock_page()
349                                  */
350                                 get_page(page); /* for putback_lru_page() */
351                                 __munlock_isolated_page(page);
352                                 unlock_page(page);
353                                 put_page(page); /* from follow_page_mask() */
354                         }
355                 }
356         }
357 
358         /*
359          * Phase 3: page putback for pages that qualified for the fast path
360          * This will also call put_page() to return pin from follow_page_mask()
361          */
362         if (pagevec_count(&pvec_putback))
363                 __putback_lru_fast(&pvec_putback, pgrescued);
364 }
365 
366 /*
367  * Fill up pagevec for __munlock_pagevec using pte walk
368  *
369  * The function expects that the struct page corresponding to @start address is
370  * a non-TPH page already pinned and in the @pvec, and that it belongs to @zone.
371  *
372  * The rest of @pvec is filled by subsequent pages within the same pmd and same
373  * zone, as long as the pte's are present and vm_normal_page() succeeds. These
374  * pages also get pinned.
375  *
376  * Returns the address of the next page that should be scanned. This equals
377  * @start + PAGE_SIZE when no page could be added by the pte walk.
378  */
379 static unsigned long __munlock_pagevec_fill(struct pagevec *pvec,
380                         struct vm_area_struct *vma, struct zone *zone,
381                         unsigned long start, unsigned long end)
382 {
383         pte_t *pte;
384         spinlock_t *ptl;
385 
386         /*
387          * Initialize pte walk starting at the already pinned page where we
388          * are sure that there is a pte, as it was pinned under the same
389          * mmap_lock write op.
390          */
391         pte = get_locked_pte(vma->vm_mm, start, &ptl);
392         /* Make sure we do not cross the page table boundary */
393         end = pgd_addr_end(start, end);
394         end = p4d_addr_end(start, end);
395         end = pud_addr_end(start, end);
396         end = pmd_addr_end(start, end);
397 
398         /* The page next to the pinned page is the first we will try to get */
399         start += PAGE_SIZE;
400         while (start < end) {
401                 struct page *page = NULL;
402                 pte++;
403                 if (pte_present(*pte))
404                         page = vm_normal_page(vma, start, *pte);
405                 /*
406                  * Break if page could not be obtained or the page's node+zone does not
407                  * match
408                  */
409                 if (!page || page_zone(page) != zone)
410                         break;
411 
412                 /*
413                  * Do not use pagevec for PTE-mapped THP,
414                  * munlock_vma_pages_range() will handle them.
415                  */
416                 if (PageTransCompound(page))
417                         break;
418 
419                 get_page(page);
420                 /*
421                  * Increase the address that will be returned *before* the
422                  * eventual break due to pvec becoming full by adding the page
423                  */
424                 start += PAGE_SIZE;
425                 if (pagevec_add(pvec, page) == 0)
426                         break;
427         }
428         pte_unmap_unlock(pte, ptl);
429         return start;
430 }
431 
432 /*
433  * munlock_vma_pages_range() - munlock all pages in the vma range.'
434  * @vma - vma containing range to be munlock()ed.
435  * @start - start address in @vma of the range
436  * @end - end of range in @vma.
437  *
438  *  For mremap(), munmap() and exit().
439  *
440  * Called with @vma VM_LOCKED.
441  *
442  * Returns with VM_LOCKED cleared.  Callers must be prepared to
443  * deal with this.
444  *
445  * We don't save and restore VM_LOCKED here because pages are
446  * still on lru.  In unmap path, pages might be scanned by reclaim
447  * and re-mlocked by try_to_{munlock|unmap} before we unmap and
448  * free them.  This will result in freeing mlocked pages.
449  */
450 void munlock_vma_pages_range(struct vm_area_struct *vma,
451                              unsigned long start, unsigned long end)
452 {
453         vma->vm_flags &= VM_LOCKED_CLEAR_MASK;
454 
455         while (start < end) {
456                 struct page *page;
457                 unsigned int page_mask = 0;
458                 unsigned long page_increm;
459                 struct pagevec pvec;
460                 struct zone *zone;
461 
462                 pagevec_init(&pvec);
463                 /*
464                  * Although FOLL_DUMP is intended for get_dump_page(),
465                  * it just so happens that its special treatment of the
466                  * ZERO_PAGE (returning an error instead of doing get_page)
467                  * suits munlock very well (and if somehow an abnormal page
468                  * has sneaked into the range, we won't oops here: great).
469                  */
470                 page = follow_page(vma, start, FOLL_GET | FOLL_DUMP);
471 
472                 if (page && !IS_ERR(page)) {
473                         if (PageTransTail(page)) {
474                                 VM_BUG_ON_PAGE(PageMlocked(page), page);
475                                 put_page(page); /* follow_page_mask() */
476                         } else if (PageTransHuge(page)) {
477                                 lock_page(page);
478                                 /*
479                                  * Any THP page found by follow_page_mask() may
480                                  * have gotten split before reaching
481                                  * munlock_vma_page(), so we need to compute
482                                  * the page_mask here instead.
483                                  */
484                                 page_mask = munlock_vma_page(page);
485                                 unlock_page(page);
486                                 put_page(page); /* follow_page_mask() */
487                         } else {
488                                 /*
489                                  * Non-huge pages are handled in batches via
490                                  * pagevec. The pin from follow_page_mask()
491                                  * prevents them from collapsing by THP.
492                                  */
493                                 pagevec_add(&pvec, page);
494                                 zone = page_zone(page);
495 
496                                 /*
497                                  * Try to fill the rest of pagevec using fast
498                                  * pte walk. This will also update start to
499                                  * the next page to process. Then munlock the
500                                  * pagevec.
501                                  */
502                                 start = __munlock_pagevec_fill(&pvec, vma,
503                                                 zone, start, end);
504                                 __munlock_pagevec(&pvec, zone);
505                                 goto next;
506                         }
507                 }
508                 page_increm = 1 + page_mask;
509                 start += page_increm * PAGE_SIZE;
510 next:
511                 cond_resched();
512         }
513 }
514 
515 /*
516  * mlock_fixup  - handle mlock[all]/munlock[all] requests.
517  *
518  * Filters out "special" vmas -- VM_LOCKED never gets set for these, and
519  * munlock is a no-op.  However, for some special vmas, we go ahead and
520  * populate the ptes.
521  *
522  * For vmas that pass the filters, merge/split as appropriate.
523  */
524 static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
525         unsigned long start, unsigned long end, vm_flags_t newflags)
526 {
527         struct mm_struct *mm = vma->vm_mm;
528         pgoff_t pgoff;
529         int nr_pages;
530         int ret = 0;
531         int lock = !!(newflags & VM_LOCKED);
532         vm_flags_t old_flags = vma->vm_flags;
533 
534         if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) ||
535             is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm) ||
536             vma_is_dax(vma))
537                 /* don't set VM_LOCKED or VM_LOCKONFAULT and don't count */
538                 goto out;
539 
540         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
541         *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
542                           vma->vm_file, pgoff, vma_policy(vma),
543                           vma->vm_userfaultfd_ctx);
544         if (*prev) {
545                 vma = *prev;
546                 goto success;
547         }
548 
549         if (start != vma->vm_start) {
550                 ret = split_vma(mm, vma, start, 1);
551                 if (ret)
552                         goto out;
553         }
554 
555         if (end != vma->vm_end) {
556                 ret = split_vma(mm, vma, end, 0);
557                 if (ret)
558                         goto out;
559         }
560 
561 success:
562         /*
563          * Keep track of amount of locked VM.
564          */
565         nr_pages = (end - start) >> PAGE_SHIFT;
566         if (!lock)
567                 nr_pages = -nr_pages;
568         else if (old_flags & VM_LOCKED)
569                 nr_pages = 0;
570         mm->locked_vm += nr_pages;
571 
572         /*
573          * vm_flags is protected by the mmap_lock held in write mode.
574          * It's okay if try_to_unmap_one unmaps a page just after we
575          * set VM_LOCKED, populate_vma_page_range will bring it back.
576          */
577 
578         if (lock)
579                 vma->vm_flags = newflags;
580         else
581                 munlock_vma_pages_range(vma, start, end);
582 
583 out:
584         *prev = vma;
585         return ret;
586 }
587 
588 static int apply_vma_lock_flags(unsigned long start, size_t len,
589                                 vm_flags_t flags)
590 {
591         unsigned long nstart, end, tmp;
592         struct vm_area_struct * vma, * prev;
593         int error;
594 
595         VM_BUG_ON(offset_in_page(start));
596         VM_BUG_ON(len != PAGE_ALIGN(len));
597         end = start + len;
598         if (end < start)
599                 return -EINVAL;
600         if (end == start)
601                 return 0;
602         vma = find_vma(current->mm, start);
603         if (!vma || vma->vm_start > start)
604                 return -ENOMEM;
605 
606         prev = vma->vm_prev;
607         if (start > vma->vm_start)
608                 prev = vma;
609 
610         for (nstart = start ; ; ) {
611                 vm_flags_t newflags = vma->vm_flags & VM_LOCKED_CLEAR_MASK;
612 
613                 newflags |= flags;
614 
615                 /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
616                 tmp = vma->vm_end;
617                 if (tmp > end)
618                         tmp = end;
619                 error = mlock_fixup(vma, &prev, nstart, tmp, newflags);
620                 if (error)
621                         break;
622                 nstart = tmp;
623                 if (nstart < prev->vm_end)
624                         nstart = prev->vm_end;
625                 if (nstart >= end)
626                         break;
627 
628                 vma = prev->vm_next;
629                 if (!vma || vma->vm_start != nstart) {
630                         error = -ENOMEM;
631                         break;
632                 }
633         }
634         return error;
635 }
636 
637 /*
638  * Go through vma areas and sum size of mlocked
639  * vma pages, as return value.
640  * Note deferred memory locking case(mlock2(,,MLOCK_ONFAULT)
641  * is also counted.
642  * Return value: previously mlocked page counts
643  */
644 static unsigned long count_mm_mlocked_page_nr(struct mm_struct *mm,
645                 unsigned long start, size_t len)
646 {
647         struct vm_area_struct *vma;
648         unsigned long count = 0;
649 
650         if (mm == NULL)
651                 mm = current->mm;
652 
653         vma = find_vma(mm, start);
654         if (vma == NULL)
655                 vma = mm->mmap;
656 
657         for (; vma ; vma = vma->vm_next) {
658                 if (start >= vma->vm_end)
659                         continue;
660                 if (start + len <=  vma->vm_start)
661                         break;
662                 if (vma->vm_flags & VM_LOCKED) {
663                         if (start > vma->vm_start)
664                                 count -= (start - vma->vm_start);
665                         if (start + len < vma->vm_end) {
666                                 count += start + len - vma->vm_start;
667                                 break;
668                         }
669                         count += vma->vm_end - vma->vm_start;
670                 }
671         }
672 
673         return count >> PAGE_SHIFT;
674 }
675 
676 static __must_check int do_mlock(unsigned long start, size_t len, vm_flags_t flags)
677 {
678         unsigned long locked;
679         unsigned long lock_limit;
680         int error = -ENOMEM;
681 
682         start = untagged_addr(start);
683 
684         if (!can_do_mlock())
685                 return -EPERM;
686 
687         len = PAGE_ALIGN(len + (offset_in_page(start)));
688         start &= PAGE_MASK;
689 
690         lock_limit = rlimit(RLIMIT_MEMLOCK);
691         lock_limit >>= PAGE_SHIFT;
692         locked = len >> PAGE_SHIFT;
693 
694         if (mmap_write_lock_killable(current->mm))
695                 return -EINTR;
696 
697         locked += current->mm->locked_vm;
698         if ((locked > lock_limit) && (!capable(CAP_IPC_LOCK))) {
699                 /*
700                  * It is possible that the regions requested intersect with
701                  * previously mlocked areas, that part area in "mm->locked_vm"
702                  * should not be counted to new mlock increment count. So check
703                  * and adjust locked count if necessary.
704                  */
705                 locked -= count_mm_mlocked_page_nr(current->mm,
706                                 start, len);
707         }
708 
709         /* check against resource limits */
710         if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
711                 error = apply_vma_lock_flags(start, len, flags);
712 
713         mmap_write_unlock(current->mm);
714         if (error)
715                 return error;
716 
717         error = __mm_populate(start, len, 0);
718         if (error)
719                 return __mlock_posix_error_return(error);
720         return 0;
721 }
722 
723 SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
724 {
725         return do_mlock(start, len, VM_LOCKED);
726 }
727 
728 SYSCALL_DEFINE3(mlock2, unsigned long, start, size_t, len, int, flags)
729 {
730         vm_flags_t vm_flags = VM_LOCKED;
731 
732         if (flags & ~MLOCK_ONFAULT)
733                 return -EINVAL;
734 
735         if (flags & MLOCK_ONFAULT)
736                 vm_flags |= VM_LOCKONFAULT;
737 
738         return do_mlock(start, len, vm_flags);
739 }
740 
741 SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
742 {
743         int ret;
744 
745         start = untagged_addr(start);
746 
747         len = PAGE_ALIGN(len + (offset_in_page(start)));
748         start &= PAGE_MASK;
749 
750         if (mmap_write_lock_killable(current->mm))
751                 return -EINTR;
752         ret = apply_vma_lock_flags(start, len, 0);
753         mmap_write_unlock(current->mm);
754 
755         return ret;
756 }
757 
758 /*
759  * Take the MCL_* flags passed into mlockall (or 0 if called from munlockall)
760  * and translate into the appropriate modifications to mm->def_flags and/or the
761  * flags for all current VMAs.
762  *
763  * There are a couple of subtleties with this.  If mlockall() is called multiple
764  * times with different flags, the values do not necessarily stack.  If mlockall
765  * is called once including the MCL_FUTURE flag and then a second time without
766  * it, VM_LOCKED and VM_LOCKONFAULT will be cleared from mm->def_flags.
767  */
768 static int apply_mlockall_flags(int flags)
769 {
770         struct vm_area_struct * vma, * prev = NULL;
771         vm_flags_t to_add = 0;
772 
773         current->mm->def_flags &= VM_LOCKED_CLEAR_MASK;
774         if (flags & MCL_FUTURE) {
775                 current->mm->def_flags |= VM_LOCKED;
776 
777                 if (flags & MCL_ONFAULT)
778                         current->mm->def_flags |= VM_LOCKONFAULT;
779 
780                 if (!(flags & MCL_CURRENT))
781                         goto out;
782         }
783 
784         if (flags & MCL_CURRENT) {
785                 to_add |= VM_LOCKED;
786                 if (flags & MCL_ONFAULT)
787                         to_add |= VM_LOCKONFAULT;
788         }
789 
790         for (vma = current->mm->mmap; vma ; vma = prev->vm_next) {
791                 vm_flags_t newflags;
792 
793                 newflags = vma->vm_flags & VM_LOCKED_CLEAR_MASK;
794                 newflags |= to_add;
795 
796                 /* Ignore errors */
797                 mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
798                 cond_resched();
799         }
800 out:
801         return 0;
802 }
803 
804 SYSCALL_DEFINE1(mlockall, int, flags)
805 {
806         unsigned long lock_limit;
807         int ret;
808 
809         if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE | MCL_ONFAULT)) ||
810             flags == MCL_ONFAULT)
811                 return -EINVAL;
812 
813         if (!can_do_mlock())
814                 return -EPERM;
815 
816         lock_limit = rlimit(RLIMIT_MEMLOCK);
817         lock_limit >>= PAGE_SHIFT;
818 
819         if (mmap_write_lock_killable(current->mm))
820                 return -EINTR;
821 
822         ret = -ENOMEM;
823         if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
824             capable(CAP_IPC_LOCK))
825                 ret = apply_mlockall_flags(flags);
826         mmap_write_unlock(current->mm);
827         if (!ret && (flags & MCL_CURRENT))
828                 mm_populate(0, TASK_SIZE);
829 
830         return ret;
831 }
832 
833 SYSCALL_DEFINE0(munlockall)
834 {
835         int ret;
836 
837         if (mmap_write_lock_killable(current->mm))
838                 return -EINTR;
839         ret = apply_mlockall_flags(0);
840         mmap_write_unlock(current->mm);
841         return ret;
842 }
843 
844 /*
845  * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
846  * shm segments) get accounted against the user_struct instead.
847  */
848 static DEFINE_SPINLOCK(shmlock_user_lock);
849 
850 int user_shm_lock(size_t size, struct user_struct *user)
851 {
852         unsigned long lock_limit, locked;
853         int allowed = 0;
854 
855         locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
856         lock_limit = rlimit(RLIMIT_MEMLOCK);
857         if (lock_limit == RLIM_INFINITY)
858                 allowed = 1;
859         lock_limit >>= PAGE_SHIFT;
860         spin_lock(&shmlock_user_lock);
861         if (!allowed &&
862             locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))
863                 goto out;
864         get_uid(user);
865         user->locked_shm += locked;
866         allowed = 1;
867 out:
868         spin_unlock(&shmlock_user_lock);
869         return allowed;
870 }
871 
872 void user_shm_unlock(size_t size, struct user_struct *user)
873 {
874         spin_lock(&shmlock_user_lock);
875         user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
876         spin_unlock(&shmlock_user_lock);
877         free_uid(user);
878 }
879 

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