Root/mm/mlock.c

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

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