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1/*
2 * linux/mm/mlock.c
3 *
4 * (C) Copyright 1995 Linus Torvalds
5 * (C) Copyright 2002 Christoph Hellwig
6 */
7
8#include <linux/capability.h>
9#include <linux/mman.h>
10#include <linux/mm.h>
11#include <linux/swap.h>
12#include <linux/swapops.h>
13#include <linux/pagemap.h>
14#include <linux/mempolicy.h>
15#include <linux/syscalls.h>
16#include <linux/sched.h>
17#include <linux/export.h>
18#include <linux/rmap.h>
19#include <linux/mmzone.h>
20#include <linux/hugetlb.h>
21
22#include "internal.h"
23
24int can_do_mlock(void)
25{
26 if (capable(CAP_IPC_LOCK))
27 return 1;
28 if (rlimit(RLIMIT_MEMLOCK) != 0)
29 return 1;
30 return 0;
31}
32EXPORT_SYMBOL(can_do_mlock);
33
34/*
35 * Mlocked pages are marked with PageMlocked() flag for efficient testing
36 * in vmscan and, possibly, the fault path; and to support semi-accurate
37 * statistics.
38 *
39 * An mlocked page [PageMlocked(page)] is unevictable. As such, it will
40 * be placed on the LRU "unevictable" list, rather than the [in]active lists.
41 * The unevictable list is an LRU sibling list to the [in]active lists.
42 * PageUnevictable is set to indicate the unevictable state.
43 *
44 * When lazy mlocking via vmscan, it is important to ensure that the
45 * vma's VM_LOCKED status is not concurrently being modified, otherwise we
46 * may have mlocked a page that is being munlocked. So lazy mlock must take
47 * the mmap_sem for read, and verify that the vma really is locked
48 * (see mm/rmap.c).
49 */
50
51/*
52 * LRU accounting for clear_page_mlock()
53 */
54void __clear_page_mlock(struct page *page)
55{
56 VM_BUG_ON(!PageLocked(page));
57
58 if (!page->mapping) { /* truncated ? */
59 return;
60 }
61
62 dec_zone_page_state(page, NR_MLOCK);
63 count_vm_event(UNEVICTABLE_PGCLEARED);
64 if (!isolate_lru_page(page)) {
65 putback_lru_page(page);
66 } else {
67 /*
68 * We lost the race. the page already moved to evictable list.
69 */
70 if (PageUnevictable(page))
71 count_vm_event(UNEVICTABLE_PGSTRANDED);
72 }
73}
74
75/*
76 * Mark page as mlocked if not already.
77 * If page on LRU, isolate and putback to move to unevictable list.
78 */
79void mlock_vma_page(struct page *page)
80{
81 BUG_ON(!PageLocked(page));
82
83 if (!TestSetPageMlocked(page)) {
84 inc_zone_page_state(page, NR_MLOCK);
85 count_vm_event(UNEVICTABLE_PGMLOCKED);
86 if (!isolate_lru_page(page))
87 putback_lru_page(page);
88 }
89}
90
91/**
92 * munlock_vma_page - munlock a vma page
93 * @page - page to be unlocked
94 *
95 * called from munlock()/munmap() path with page supposedly on the LRU.
96 * When we munlock a page, because the vma where we found the page is being
97 * munlock()ed or munmap()ed, we want to check whether other vmas hold the
98 * page locked so that we can leave it on the unevictable lru list and not
99 * bother vmscan with it. However, to walk the page's rmap list in
100 * try_to_munlock() we must isolate the page from the LRU. If some other
101 * task has removed the page from the LRU, we won't be able to do that.
102 * So we clear the PageMlocked as we might not get another chance. If we
103 * can't isolate the page, we leave it for putback_lru_page() and vmscan
104 * [page_referenced()/try_to_unmap()] to deal with.
105 */
106void munlock_vma_page(struct page *page)
107{
108 BUG_ON(!PageLocked(page));
109
110 if (TestClearPageMlocked(page)) {
111 dec_zone_page_state(page, NR_MLOCK);
112 if (!isolate_lru_page(page)) {
113 int ret = SWAP_AGAIN;
114
115 /*
116 * Optimization: if the page was mapped just once,
117 * that's our mapping and we don't need to check all the
118 * other vmas.
119 */
120 if (page_mapcount(page) > 1)
121 ret = try_to_munlock(page);
122 /*
123 * did try_to_unlock() succeed or punt?
124 */
125 if (ret != SWAP_MLOCK)
126 count_vm_event(UNEVICTABLE_PGMUNLOCKED);
127
128 putback_lru_page(page);
129 } else {
130 /*
131 * Some other task has removed the page from the LRU.
132 * putback_lru_page() will take care of removing the
133 * page from the unevictable list, if necessary.
134 * vmscan [page_referenced()] will move the page back
135 * to the unevictable list if some other vma has it
136 * mlocked.
137 */
138 if (PageUnevictable(page))
139 count_vm_event(UNEVICTABLE_PGSTRANDED);
140 else
141 count_vm_event(UNEVICTABLE_PGMUNLOCKED);
142 }
143 }
144}
145
146/**
147 * __mlock_vma_pages_range() - mlock a range of pages in the vma.
148 * @vma: target vma
149 * @start: start address
150 * @end: end address
151 *
152 * This takes care of making the pages present too.
153 *
154 * return 0 on success, negative error code on error.
155 *
156 * vma->vm_mm->mmap_sem must be held for at least read.
157 */
158static long __mlock_vma_pages_range(struct vm_area_struct *vma,
159 unsigned long start, unsigned long end,
160 int *nonblocking)
161{
162 struct mm_struct *mm = vma->vm_mm;
163 unsigned long addr = start;
164 int nr_pages = (end - start) / PAGE_SIZE;
165 int gup_flags;
166
167 VM_BUG_ON(start & ~PAGE_MASK);
168 VM_BUG_ON(end & ~PAGE_MASK);
169 VM_BUG_ON(start < vma->vm_start);
170 VM_BUG_ON(end > vma->vm_end);
171 VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
172
173 gup_flags = FOLL_TOUCH | FOLL_MLOCK;
174 /*
175 * We want to touch writable mappings with a write fault in order
176 * to break COW, except for shared mappings because these don't COW
177 * and we would not want to dirty them for nothing.
178 */
179 if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
180 gup_flags |= FOLL_WRITE;
181
182 /*
183 * We want mlock to succeed for regions that have any permissions
184 * other than PROT_NONE.
185 */
186 if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC))
187 gup_flags |= FOLL_FORCE;
188
189 return __get_user_pages(current, mm, addr, nr_pages, gup_flags,
190 NULL, NULL, nonblocking);
191}
192
193/*
194 * convert get_user_pages() return value to posix mlock() error
195 */
196static int __mlock_posix_error_return(long retval)
197{
198 if (retval == -EFAULT)
199 retval = -ENOMEM;
200 else if (retval == -ENOMEM)
201 retval = -EAGAIN;
202 return retval;
203}
204
205/**
206 * mlock_vma_pages_range() - mlock pages in specified vma range.
207 * @vma - the vma containing the specfied address range
208 * @start - starting address in @vma to mlock
209 * @end - end address [+1] in @vma to mlock
210 *
211 * For mmap()/mremap()/expansion of mlocked vma.
212 *
213 * return 0 on success for "normal" vmas.
214 *
215 * return number of pages [> 0] to be removed from locked_vm on success
216 * of "special" vmas.
217 */
218long mlock_vma_pages_range(struct vm_area_struct *vma,
219 unsigned long start, unsigned long end)
220{
221 int nr_pages = (end - start) / PAGE_SIZE;
222 BUG_ON(!(vma->vm_flags & VM_LOCKED));
223
224 /*
225 * filter unlockable vmas
226 */
227 if (vma->vm_flags & (VM_IO | VM_PFNMAP))
228 goto no_mlock;
229
230 if (!((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
231 is_vm_hugetlb_page(vma) ||
232 vma == get_gate_vma(current->mm))) {
233
234 __mlock_vma_pages_range(vma, start, end, NULL);
235
236 /* Hide errors from mmap() and other callers */
237 return 0;
238 }
239
240 /*
241 * User mapped kernel pages or huge pages:
242 * make these pages present to populate the ptes, but
243 * fall thru' to reset VM_LOCKED--no need to unlock, and
244 * return nr_pages so these don't get counted against task's
245 * locked limit. huge pages are already counted against
246 * locked vm limit.
247 */
248 make_pages_present(start, end);
249
250no_mlock:
251 vma->vm_flags &= ~VM_LOCKED; /* and don't come back! */
252 return nr_pages; /* error or pages NOT mlocked */
253}
254
255/*
256 * munlock_vma_pages_range() - munlock all pages in the vma range.'
257 * @vma - vma containing range to be munlock()ed.
258 * @start - start address in @vma of the range
259 * @end - end of range in @vma.
260 *
261 * For mremap(), munmap() and exit().
262 *
263 * Called with @vma VM_LOCKED.
264 *
265 * Returns with VM_LOCKED cleared. Callers must be prepared to
266 * deal with this.
267 *
268 * We don't save and restore VM_LOCKED here because pages are
269 * still on lru. In unmap path, pages might be scanned by reclaim
270 * and re-mlocked by try_to_{munlock|unmap} before we unmap and
271 * free them. This will result in freeing mlocked pages.
272 */
273void munlock_vma_pages_range(struct vm_area_struct *vma,
274 unsigned long start, unsigned long end)
275{
276 unsigned long addr;
277
278 lru_add_drain();
279 vma->vm_flags &= ~VM_LOCKED;
280
281 for (addr = start; addr < end; addr += PAGE_SIZE) {
282 struct page *page;
283 /*
284 * Although FOLL_DUMP is intended for get_dump_page(),
285 * it just so happens that its special treatment of the
286 * ZERO_PAGE (returning an error instead of doing get_page)
287 * suits munlock very well (and if somehow an abnormal page
288 * has sneaked into the range, we won't oops here: great).
289 */
290 page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
291 if (page && !IS_ERR(page)) {
292 lock_page(page);
293 /*
294 * Like in __mlock_vma_pages_range(),
295 * because we lock page here and migration is
296 * blocked by the elevated reference, we need
297 * only check for file-cache page truncation.
298 */
299 if (page->mapping)
300 munlock_vma_page(page);
301 unlock_page(page);
302 put_page(page);
303 }
304 cond_resched();
305 }
306}
307
308/*
309 * mlock_fixup - handle mlock[all]/munlock[all] requests.
310 *
311 * Filters out "special" vmas -- VM_LOCKED never gets set for these, and
312 * munlock is a no-op. However, for some special vmas, we go ahead and
313 * populate the ptes via make_pages_present().
314 *
315 * For vmas that pass the filters, merge/split as appropriate.
316 */
317static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
318 unsigned long start, unsigned long end, vm_flags_t newflags)
319{
320 struct mm_struct *mm = vma->vm_mm;
321 pgoff_t pgoff;
322 int nr_pages;
323 int ret = 0;
324 int lock = !!(newflags & VM_LOCKED);
325
326 if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) ||
327 is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm))
328 goto out; /* don't set VM_LOCKED, don't count */
329
330 pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
331 *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
332 vma->vm_file, pgoff, vma_policy(vma));
333 if (*prev) {
334 vma = *prev;
335 goto success;
336 }
337
338 if (start != vma->vm_start) {
339 ret = split_vma(mm, vma, start, 1);
340 if (ret)
341 goto out;
342 }
343
344 if (end != vma->vm_end) {
345 ret = split_vma(mm, vma, end, 0);
346 if (ret)
347 goto out;
348 }
349
350success:
351 /*
352 * Keep track of amount of locked VM.
353 */
354 nr_pages = (end - start) >> PAGE_SHIFT;
355 if (!lock)
356 nr_pages = -nr_pages;
357 mm->locked_vm += nr_pages;
358
359 /*
360 * vm_flags is protected by the mmap_sem held in write mode.
361 * It's okay if try_to_unmap_one unmaps a page just after we
362 * set VM_LOCKED, __mlock_vma_pages_range will bring it back.
363 */
364
365 if (lock)
366 vma->vm_flags = newflags;
367 else
368 munlock_vma_pages_range(vma, start, end);
369
370out:
371 *prev = vma;
372 return ret;
373}
374
375static int do_mlock(unsigned long start, size_t len, int on)
376{
377 unsigned long nstart, end, tmp;
378 struct vm_area_struct * vma, * prev;
379 int error;
380
381 VM_BUG_ON(start & ~PAGE_MASK);
382 VM_BUG_ON(len != PAGE_ALIGN(len));
383 end = start + len;
384 if (end < start)
385 return -EINVAL;
386 if (end == start)
387 return 0;
388 vma = find_vma(current->mm, start);
389 if (!vma || vma->vm_start > start)
390 return -ENOMEM;
391
392 prev = vma->vm_prev;
393 if (start > vma->vm_start)
394 prev = vma;
395
396 for (nstart = start ; ; ) {
397 vm_flags_t newflags;
398
399 /* Here we know that vma->vm_start <= nstart < vma->vm_end. */
400
401 newflags = vma->vm_flags | VM_LOCKED;
402 if (!on)
403 newflags &= ~VM_LOCKED;
404
405 tmp = vma->vm_end;
406 if (tmp > end)
407 tmp = end;
408 error = mlock_fixup(vma, &prev, nstart, tmp, newflags);
409 if (error)
410 break;
411 nstart = tmp;
412 if (nstart < prev->vm_end)
413 nstart = prev->vm_end;
414 if (nstart >= end)
415 break;
416
417 vma = prev->vm_next;
418 if (!vma || vma->vm_start != nstart) {
419 error = -ENOMEM;
420 break;
421 }
422 }
423 return error;
424}
425
426static int do_mlock_pages(unsigned long start, size_t len, int ignore_errors)
427{
428 struct mm_struct *mm = current->mm;
429 unsigned long end, nstart, nend;
430 struct vm_area_struct *vma = NULL;
431 int locked = 0;
432 int ret = 0;
433
434 VM_BUG_ON(start & ~PAGE_MASK);
435 VM_BUG_ON(len != PAGE_ALIGN(len));
436 end = start + len;
437
438 for (nstart = start; nstart < end; nstart = nend) {
439 /*
440 * We want to fault in pages for [nstart; end) address range.
441 * Find first corresponding VMA.
442 */
443 if (!locked) {
444 locked = 1;
445 down_read(&mm->mmap_sem);
446 vma = find_vma(mm, nstart);
447 } else if (nstart >= vma->vm_end)
448 vma = vma->vm_next;
449 if (!vma || vma->vm_start >= end)
450 break;
451 /*
452 * Set [nstart; nend) to intersection of desired address
453 * range with the first VMA. Also, skip undesirable VMA types.
454 */
455 nend = min(end, vma->vm_end);
456 if (vma->vm_flags & (VM_IO | VM_PFNMAP))
457 continue;
458 if (nstart < vma->vm_start)
459 nstart = vma->vm_start;
460 /*
461 * Now fault in a range of pages. __mlock_vma_pages_range()
462 * double checks the vma flags, so that it won't mlock pages
463 * if the vma was already munlocked.
464 */
465 ret = __mlock_vma_pages_range(vma, nstart, nend, &locked);
466 if (ret < 0) {
467 if (ignore_errors) {
468 ret = 0;
469 continue; /* continue at next VMA */
470 }
471 ret = __mlock_posix_error_return(ret);
472 break;
473 }
474 nend = nstart + ret * PAGE_SIZE;
475 ret = 0;
476 }
477 if (locked)
478 up_read(&mm->mmap_sem);
479 return ret; /* 0 or negative error code */
480}
481
482SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
483{
484 unsigned long locked;
485 unsigned long lock_limit;
486 int error = -ENOMEM;
487
488 if (!can_do_mlock())
489 return -EPERM;
490
491 lru_add_drain_all(); /* flush pagevec */
492
493 down_write(¤t->mm->mmap_sem);
494 len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
495 start &= PAGE_MASK;
496
497 locked = len >> PAGE_SHIFT;
498 locked += current->mm->locked_vm;
499
500 lock_limit = rlimit(RLIMIT_MEMLOCK);
501 lock_limit >>= PAGE_SHIFT;
502
503 /* check against resource limits */
504 if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
505 error = do_mlock(start, len, 1);
506 up_write(¤t->mm->mmap_sem);
507 if (!error)
508 error = do_mlock_pages(start, len, 0);
509 return error;
510}
511
512SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
513{
514 int ret;
515
516 down_write(¤t->mm->mmap_sem);
517 len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
518 start &= PAGE_MASK;
519 ret = do_mlock(start, len, 0);
520 up_write(¤t->mm->mmap_sem);
521 return ret;
522}
523
524static int do_mlockall(int flags)
525{
526 struct vm_area_struct * vma, * prev = NULL;
527 unsigned int def_flags = 0;
528
529 if (flags & MCL_FUTURE)
530 def_flags = VM_LOCKED;
531 current->mm->def_flags = def_flags;
532 if (flags == MCL_FUTURE)
533 goto out;
534
535 for (vma = current->mm->mmap; vma ; vma = prev->vm_next) {
536 vm_flags_t newflags;
537
538 newflags = vma->vm_flags | VM_LOCKED;
539 if (!(flags & MCL_CURRENT))
540 newflags &= ~VM_LOCKED;
541
542 /* Ignore errors */
543 mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
544 }
545out:
546 return 0;
547}
548
549SYSCALL_DEFINE1(mlockall, int, flags)
550{
551 unsigned long lock_limit;
552 int ret = -EINVAL;
553
554 if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE)))
555 goto out;
556
557 ret = -EPERM;
558 if (!can_do_mlock())
559 goto out;
560
561 if (flags & MCL_CURRENT)
562 lru_add_drain_all(); /* flush pagevec */
563
564 down_write(¤t->mm->mmap_sem);
565
566 lock_limit = rlimit(RLIMIT_MEMLOCK);
567 lock_limit >>= PAGE_SHIFT;
568
569 ret = -ENOMEM;
570 if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
571 capable(CAP_IPC_LOCK))
572 ret = do_mlockall(flags);
573 up_write(¤t->mm->mmap_sem);
574 if (!ret && (flags & MCL_CURRENT)) {
575 /* Ignore errors */
576 do_mlock_pages(0, TASK_SIZE, 1);
577 }
578out:
579 return ret;
580}
581
582SYSCALL_DEFINE0(munlockall)
583{
584 int ret;
585
586 down_write(¤t->mm->mmap_sem);
587 ret = do_mlockall(0);
588 up_write(¤t->mm->mmap_sem);
589 return ret;
590}
591
592/*
593 * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
594 * shm segments) get accounted against the user_struct instead.
595 */
596static DEFINE_SPINLOCK(shmlock_user_lock);
597
598int user_shm_lock(size_t size, struct user_struct *user)
599{
600 unsigned long lock_limit, locked;
601 int allowed = 0;
602
603 locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
604 lock_limit = rlimit(RLIMIT_MEMLOCK);
605 if (lock_limit == RLIM_INFINITY)
606 allowed = 1;
607 lock_limit >>= PAGE_SHIFT;
608 spin_lock(&shmlock_user_lock);
609 if (!allowed &&
610 locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))
611 goto out;
612 get_uid(user);
613 user->locked_shm += locked;
614 allowed = 1;
615out:
616 spin_unlock(&shmlock_user_lock);
617 return allowed;
618}
619
620void user_shm_unlock(size_t size, struct user_struct *user)
621{
622 spin_lock(&shmlock_user_lock);
623 user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
624 spin_unlock(&shmlock_user_lock);
625 free_uid(user);
626}