xref: /openbmc/linux/mm/mlock.c (revision b6dcefde)
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/module.h>
18 #include <linux/rmap.h>
19 #include <linux/mmzone.h>
20 #include <linux/hugetlb.h>
21 
22 #include "internal.h"
23 
24 int can_do_mlock(void)
25 {
26 	if (capable(CAP_IPC_LOCK))
27 		return 1;
28 	if (current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur != 0)
29 		return 1;
30 	return 0;
31 }
32 EXPORT_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  */
54 void __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  */
79 void 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  */
106 void 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 = try_to_munlock(page);
114 			/*
115 			 * did try_to_unlock() succeed or punt?
116 			 */
117 			if (ret != SWAP_MLOCK)
118 				count_vm_event(UNEVICTABLE_PGMUNLOCKED);
119 
120 			putback_lru_page(page);
121 		} else {
122 			/*
123 			 * Some other task has removed the page from the LRU.
124 			 * putback_lru_page() will take care of removing the
125 			 * page from the unevictable list, if necessary.
126 			 * vmscan [page_referenced()] will move the page back
127 			 * to the unevictable list if some other vma has it
128 			 * mlocked.
129 			 */
130 			if (PageUnevictable(page))
131 				count_vm_event(UNEVICTABLE_PGSTRANDED);
132 			else
133 				count_vm_event(UNEVICTABLE_PGMUNLOCKED);
134 		}
135 	}
136 }
137 
138 /**
139  * __mlock_vma_pages_range() -  mlock a range of pages in the vma.
140  * @vma:   target vma
141  * @start: start address
142  * @end:   end address
143  *
144  * This takes care of making the pages present too.
145  *
146  * return 0 on success, negative error code on error.
147  *
148  * vma->vm_mm->mmap_sem must be held for at least read.
149  */
150 static long __mlock_vma_pages_range(struct vm_area_struct *vma,
151 				    unsigned long start, unsigned long end)
152 {
153 	struct mm_struct *mm = vma->vm_mm;
154 	unsigned long addr = start;
155 	struct page *pages[16]; /* 16 gives a reasonable batch */
156 	int nr_pages = (end - start) / PAGE_SIZE;
157 	int ret = 0;
158 	int gup_flags;
159 
160 	VM_BUG_ON(start & ~PAGE_MASK);
161 	VM_BUG_ON(end   & ~PAGE_MASK);
162 	VM_BUG_ON(start < vma->vm_start);
163 	VM_BUG_ON(end   > vma->vm_end);
164 	VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
165 
166 	gup_flags = FOLL_TOUCH | FOLL_GET;
167 	if (vma->vm_flags & VM_WRITE)
168 		gup_flags |= FOLL_WRITE;
169 
170 	while (nr_pages > 0) {
171 		int i;
172 
173 		cond_resched();
174 
175 		/*
176 		 * get_user_pages makes pages present if we are
177 		 * setting mlock. and this extra reference count will
178 		 * disable migration of this page.  However, page may
179 		 * still be truncated out from under us.
180 		 */
181 		ret = __get_user_pages(current, mm, addr,
182 				min_t(int, nr_pages, ARRAY_SIZE(pages)),
183 				gup_flags, pages, NULL);
184 		/*
185 		 * This can happen for, e.g., VM_NONLINEAR regions before
186 		 * a page has been allocated and mapped at a given offset,
187 		 * or for addresses that map beyond end of a file.
188 		 * We'll mlock the pages if/when they get faulted in.
189 		 */
190 		if (ret < 0)
191 			break;
192 
193 		lru_add_drain();	/* push cached pages to LRU */
194 
195 		for (i = 0; i < ret; i++) {
196 			struct page *page = pages[i];
197 
198 			if (page->mapping) {
199 				/*
200 				 * That preliminary check is mainly to avoid
201 				 * the pointless overhead of lock_page on the
202 				 * ZERO_PAGE: which might bounce very badly if
203 				 * there is contention.  However, we're still
204 				 * dirtying its cacheline with get/put_page:
205 				 * we'll add another __get_user_pages flag to
206 				 * avoid it if that case turns out to matter.
207 				 */
208 				lock_page(page);
209 				/*
210 				 * Because we lock page here and migration is
211 				 * blocked by the elevated reference, we need
212 				 * only check for file-cache page truncation.
213 				 */
214 				if (page->mapping)
215 					mlock_vma_page(page);
216 				unlock_page(page);
217 			}
218 			put_page(page);	/* ref from get_user_pages() */
219 		}
220 
221 		addr += ret * PAGE_SIZE;
222 		nr_pages -= ret;
223 		ret = 0;
224 	}
225 
226 	return ret;	/* 0 or negative error code */
227 }
228 
229 /*
230  * convert get_user_pages() return value to posix mlock() error
231  */
232 static int __mlock_posix_error_return(long retval)
233 {
234 	if (retval == -EFAULT)
235 		retval = -ENOMEM;
236 	else if (retval == -ENOMEM)
237 		retval = -EAGAIN;
238 	return retval;
239 }
240 
241 /**
242  * mlock_vma_pages_range() - mlock pages in specified vma range.
243  * @vma - the vma containing the specfied address range
244  * @start - starting address in @vma to mlock
245  * @end   - end address [+1] in @vma to mlock
246  *
247  * For mmap()/mremap()/expansion of mlocked vma.
248  *
249  * return 0 on success for "normal" vmas.
250  *
251  * return number of pages [> 0] to be removed from locked_vm on success
252  * of "special" vmas.
253  */
254 long mlock_vma_pages_range(struct vm_area_struct *vma,
255 			unsigned long start, unsigned long end)
256 {
257 	int nr_pages = (end - start) / PAGE_SIZE;
258 	BUG_ON(!(vma->vm_flags & VM_LOCKED));
259 
260 	/*
261 	 * filter unlockable vmas
262 	 */
263 	if (vma->vm_flags & (VM_IO | VM_PFNMAP))
264 		goto no_mlock;
265 
266 	if (!((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
267 			is_vm_hugetlb_page(vma) ||
268 			vma == get_gate_vma(current))) {
269 
270 		__mlock_vma_pages_range(vma, start, end);
271 
272 		/* Hide errors from mmap() and other callers */
273 		return 0;
274 	}
275 
276 	/*
277 	 * User mapped kernel pages or huge pages:
278 	 * make these pages present to populate the ptes, but
279 	 * fall thru' to reset VM_LOCKED--no need to unlock, and
280 	 * return nr_pages so these don't get counted against task's
281 	 * locked limit.  huge pages are already counted against
282 	 * locked vm limit.
283 	 */
284 	make_pages_present(start, end);
285 
286 no_mlock:
287 	vma->vm_flags &= ~VM_LOCKED;	/* and don't come back! */
288 	return nr_pages;		/* error or pages NOT mlocked */
289 }
290 
291 /*
292  * munlock_vma_pages_range() - munlock all pages in the vma range.'
293  * @vma - vma containing range to be munlock()ed.
294  * @start - start address in @vma of the range
295  * @end - end of range in @vma.
296  *
297  *  For mremap(), munmap() and exit().
298  *
299  * Called with @vma VM_LOCKED.
300  *
301  * Returns with VM_LOCKED cleared.  Callers must be prepared to
302  * deal with this.
303  *
304  * We don't save and restore VM_LOCKED here because pages are
305  * still on lru.  In unmap path, pages might be scanned by reclaim
306  * and re-mlocked by try_to_{munlock|unmap} before we unmap and
307  * free them.  This will result in freeing mlocked pages.
308  */
309 void munlock_vma_pages_range(struct vm_area_struct *vma,
310 			     unsigned long start, unsigned long end)
311 {
312 	unsigned long addr;
313 
314 	lru_add_drain();
315 	vma->vm_flags &= ~VM_LOCKED;
316 
317 	for (addr = start; addr < end; addr += PAGE_SIZE) {
318 		struct page *page;
319 		/*
320 		 * Although FOLL_DUMP is intended for get_dump_page(),
321 		 * it just so happens that its special treatment of the
322 		 * ZERO_PAGE (returning an error instead of doing get_page)
323 		 * suits munlock very well (and if somehow an abnormal page
324 		 * has sneaked into the range, we won't oops here: great).
325 		 */
326 		page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
327 		if (page && !IS_ERR(page)) {
328 			lock_page(page);
329 			/*
330 			 * Like in __mlock_vma_pages_range(),
331 			 * because we lock page here and migration is
332 			 * blocked by the elevated reference, we need
333 			 * only check for file-cache page truncation.
334 			 */
335 			if (page->mapping)
336 				munlock_vma_page(page);
337 			unlock_page(page);
338 			put_page(page);
339 		}
340 		cond_resched();
341 	}
342 }
343 
344 /*
345  * mlock_fixup  - handle mlock[all]/munlock[all] requests.
346  *
347  * Filters out "special" vmas -- VM_LOCKED never gets set for these, and
348  * munlock is a no-op.  However, for some special vmas, we go ahead and
349  * populate the ptes via make_pages_present().
350  *
351  * For vmas that pass the filters, merge/split as appropriate.
352  */
353 static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
354 	unsigned long start, unsigned long end, unsigned int newflags)
355 {
356 	struct mm_struct *mm = vma->vm_mm;
357 	pgoff_t pgoff;
358 	int nr_pages;
359 	int ret = 0;
360 	int lock = newflags & VM_LOCKED;
361 
362 	if (newflags == vma->vm_flags ||
363 			(vma->vm_flags & (VM_IO | VM_PFNMAP)))
364 		goto out;	/* don't set VM_LOCKED,  don't count */
365 
366 	if ((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
367 			is_vm_hugetlb_page(vma) ||
368 			vma == get_gate_vma(current)) {
369 		if (lock)
370 			make_pages_present(start, end);
371 		goto out;	/* don't set VM_LOCKED,  don't count */
372 	}
373 
374 	pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
375 	*prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
376 			  vma->vm_file, pgoff, vma_policy(vma));
377 	if (*prev) {
378 		vma = *prev;
379 		goto success;
380 	}
381 
382 	if (start != vma->vm_start) {
383 		ret = split_vma(mm, vma, start, 1);
384 		if (ret)
385 			goto out;
386 	}
387 
388 	if (end != vma->vm_end) {
389 		ret = split_vma(mm, vma, end, 0);
390 		if (ret)
391 			goto out;
392 	}
393 
394 success:
395 	/*
396 	 * Keep track of amount of locked VM.
397 	 */
398 	nr_pages = (end - start) >> PAGE_SHIFT;
399 	if (!lock)
400 		nr_pages = -nr_pages;
401 	mm->locked_vm += nr_pages;
402 
403 	/*
404 	 * vm_flags is protected by the mmap_sem held in write mode.
405 	 * It's okay if try_to_unmap_one unmaps a page just after we
406 	 * set VM_LOCKED, __mlock_vma_pages_range will bring it back.
407 	 */
408 
409 	if (lock) {
410 		vma->vm_flags = newflags;
411 		ret = __mlock_vma_pages_range(vma, start, end);
412 		if (ret < 0)
413 			ret = __mlock_posix_error_return(ret);
414 	} else {
415 		munlock_vma_pages_range(vma, start, end);
416 	}
417 
418 out:
419 	*prev = vma;
420 	return ret;
421 }
422 
423 static int do_mlock(unsigned long start, size_t len, int on)
424 {
425 	unsigned long nstart, end, tmp;
426 	struct vm_area_struct * vma, * prev;
427 	int error;
428 
429 	len = PAGE_ALIGN(len);
430 	end = start + len;
431 	if (end < start)
432 		return -EINVAL;
433 	if (end == start)
434 		return 0;
435 	vma = find_vma_prev(current->mm, start, &prev);
436 	if (!vma || vma->vm_start > start)
437 		return -ENOMEM;
438 
439 	if (start > vma->vm_start)
440 		prev = vma;
441 
442 	for (nstart = start ; ; ) {
443 		unsigned int newflags;
444 
445 		/* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
446 
447 		newflags = vma->vm_flags | VM_LOCKED;
448 		if (!on)
449 			newflags &= ~VM_LOCKED;
450 
451 		tmp = vma->vm_end;
452 		if (tmp > end)
453 			tmp = end;
454 		error = mlock_fixup(vma, &prev, nstart, tmp, newflags);
455 		if (error)
456 			break;
457 		nstart = tmp;
458 		if (nstart < prev->vm_end)
459 			nstart = prev->vm_end;
460 		if (nstart >= end)
461 			break;
462 
463 		vma = prev->vm_next;
464 		if (!vma || vma->vm_start != nstart) {
465 			error = -ENOMEM;
466 			break;
467 		}
468 	}
469 	return error;
470 }
471 
472 SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
473 {
474 	unsigned long locked;
475 	unsigned long lock_limit;
476 	int error = -ENOMEM;
477 
478 	if (!can_do_mlock())
479 		return -EPERM;
480 
481 	lru_add_drain_all();	/* flush pagevec */
482 
483 	down_write(&current->mm->mmap_sem);
484 	len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
485 	start &= PAGE_MASK;
486 
487 	locked = len >> PAGE_SHIFT;
488 	locked += current->mm->locked_vm;
489 
490 	lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
491 	lock_limit >>= PAGE_SHIFT;
492 
493 	/* check against resource limits */
494 	if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
495 		error = do_mlock(start, len, 1);
496 	up_write(&current->mm->mmap_sem);
497 	return error;
498 }
499 
500 SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
501 {
502 	int ret;
503 
504 	down_write(&current->mm->mmap_sem);
505 	len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
506 	start &= PAGE_MASK;
507 	ret = do_mlock(start, len, 0);
508 	up_write(&current->mm->mmap_sem);
509 	return ret;
510 }
511 
512 static int do_mlockall(int flags)
513 {
514 	struct vm_area_struct * vma, * prev = NULL;
515 	unsigned int def_flags = 0;
516 
517 	if (flags & MCL_FUTURE)
518 		def_flags = VM_LOCKED;
519 	current->mm->def_flags = def_flags;
520 	if (flags == MCL_FUTURE)
521 		goto out;
522 
523 	for (vma = current->mm->mmap; vma ; vma = prev->vm_next) {
524 		unsigned int newflags;
525 
526 		newflags = vma->vm_flags | VM_LOCKED;
527 		if (!(flags & MCL_CURRENT))
528 			newflags &= ~VM_LOCKED;
529 
530 		/* Ignore errors */
531 		mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
532 	}
533 out:
534 	return 0;
535 }
536 
537 SYSCALL_DEFINE1(mlockall, int, flags)
538 {
539 	unsigned long lock_limit;
540 	int ret = -EINVAL;
541 
542 	if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE)))
543 		goto out;
544 
545 	ret = -EPERM;
546 	if (!can_do_mlock())
547 		goto out;
548 
549 	lru_add_drain_all();	/* flush pagevec */
550 
551 	down_write(&current->mm->mmap_sem);
552 
553 	lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
554 	lock_limit >>= PAGE_SHIFT;
555 
556 	ret = -ENOMEM;
557 	if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
558 	    capable(CAP_IPC_LOCK))
559 		ret = do_mlockall(flags);
560 	up_write(&current->mm->mmap_sem);
561 out:
562 	return ret;
563 }
564 
565 SYSCALL_DEFINE0(munlockall)
566 {
567 	int ret;
568 
569 	down_write(&current->mm->mmap_sem);
570 	ret = do_mlockall(0);
571 	up_write(&current->mm->mmap_sem);
572 	return ret;
573 }
574 
575 /*
576  * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
577  * shm segments) get accounted against the user_struct instead.
578  */
579 static DEFINE_SPINLOCK(shmlock_user_lock);
580 
581 int user_shm_lock(size_t size, struct user_struct *user)
582 {
583 	unsigned long lock_limit, locked;
584 	int allowed = 0;
585 
586 	locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
587 	lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
588 	if (lock_limit == RLIM_INFINITY)
589 		allowed = 1;
590 	lock_limit >>= PAGE_SHIFT;
591 	spin_lock(&shmlock_user_lock);
592 	if (!allowed &&
593 	    locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))
594 		goto out;
595 	get_uid(user);
596 	user->locked_shm += locked;
597 	allowed = 1;
598 out:
599 	spin_unlock(&shmlock_user_lock);
600 	return allowed;
601 }
602 
603 void user_shm_unlock(size_t size, struct user_struct *user)
604 {
605 	spin_lock(&shmlock_user_lock);
606 	user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
607 	spin_unlock(&shmlock_user_lock);
608 	free_uid(user);
609 }
610 
611 int account_locked_memory(struct mm_struct *mm, struct rlimit *rlim,
612 			  size_t size)
613 {
614 	unsigned long lim, vm, pgsz;
615 	int error = -ENOMEM;
616 
617 	pgsz = PAGE_ALIGN(size) >> PAGE_SHIFT;
618 
619 	down_write(&mm->mmap_sem);
620 
621 	lim = rlim[RLIMIT_AS].rlim_cur >> PAGE_SHIFT;
622 	vm   = mm->total_vm + pgsz;
623 	if (lim < vm)
624 		goto out;
625 
626 	lim = rlim[RLIMIT_MEMLOCK].rlim_cur >> PAGE_SHIFT;
627 	vm   = mm->locked_vm + pgsz;
628 	if (lim < vm)
629 		goto out;
630 
631 	mm->total_vm  += pgsz;
632 	mm->locked_vm += pgsz;
633 
634 	error = 0;
635  out:
636 	up_write(&mm->mmap_sem);
637 	return error;
638 }
639 
640 void refund_locked_memory(struct mm_struct *mm, size_t size)
641 {
642 	unsigned long pgsz = PAGE_ALIGN(size) >> PAGE_SHIFT;
643 
644 	down_write(&mm->mmap_sem);
645 
646 	mm->total_vm  -= pgsz;
647 	mm->locked_vm -= pgsz;
648 
649 	up_write(&mm->mmap_sem);
650 }
651