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
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 */
150static long __mlock_vma_pages_range(struct vm_area_struct *vma,
151                    unsigned long start, unsigned long end,
152                    int *nonblocking)
153{
154    struct mm_struct *mm = vma->vm_mm;
155    unsigned long addr = start;
156    int nr_pages = (end - start) / PAGE_SIZE;
157    int gup_flags;
158
159    VM_BUG_ON(start & ~PAGE_MASK);
160    VM_BUG_ON(end & ~PAGE_MASK);
161    VM_BUG_ON(start < vma->vm_start);
162    VM_BUG_ON(end > vma->vm_end);
163    VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
164
165    gup_flags = FOLL_TOUCH | FOLL_MLOCK;
166    /*
167     * We want to touch writable mappings with a write fault in order
168     * to break COW, except for shared mappings because these don't COW
169     * and we would not want to dirty them for nothing.
170     */
171    if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
172        gup_flags |= FOLL_WRITE;
173
174    /*
175     * We want mlock to succeed for regions that have any permissions
176     * other than PROT_NONE.
177     */
178    if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC))
179        gup_flags |= FOLL_FORCE;
180
181    return __get_user_pages(current, mm, addr, nr_pages, gup_flags,
182                NULL, NULL, nonblocking);
183}
184
185/*
186 * convert get_user_pages() return value to posix mlock() error
187 */
188static int __mlock_posix_error_return(long retval)
189{
190    if (retval == -EFAULT)
191        retval = -ENOMEM;
192    else if (retval == -ENOMEM)
193        retval = -EAGAIN;
194    return retval;
195}
196
197/**
198 * mlock_vma_pages_range() - mlock pages in specified vma range.
199 * @vma - the vma containing the specfied address range
200 * @start - starting address in @vma to mlock
201 * @end - end address [+1] in @vma to mlock
202 *
203 * For mmap()/mremap()/expansion of mlocked vma.
204 *
205 * return 0 on success for "normal" vmas.
206 *
207 * return number of pages [> 0] to be removed from locked_vm on success
208 * of "special" vmas.
209 */
210long mlock_vma_pages_range(struct vm_area_struct *vma,
211            unsigned long start, unsigned long end)
212{
213    int nr_pages = (end - start) / PAGE_SIZE;
214    BUG_ON(!(vma->vm_flags & VM_LOCKED));
215
216    /*
217     * filter unlockable vmas
218     */
219    if (vma->vm_flags & (VM_IO | VM_PFNMAP))
220        goto no_mlock;
221
222    if (!((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
223            is_vm_hugetlb_page(vma) ||
224            vma == get_gate_vma(current->mm))) {
225
226        __mlock_vma_pages_range(vma, start, end, NULL);
227
228        /* Hide errors from mmap() and other callers */
229        return 0;
230    }
231
232    /*
233     * User mapped kernel pages or huge pages:
234     * make these pages present to populate the ptes, but
235     * fall thru' to reset VM_LOCKED--no need to unlock, and
236     * return nr_pages so these don't get counted against task's
237     * locked limit. huge pages are already counted against
238     * locked vm limit.
239     */
240    make_pages_present(start, end);
241
242no_mlock:
243    vma->vm_flags &= ~VM_LOCKED; /* and don't come back! */
244    return nr_pages; /* error or pages NOT mlocked */
245}
246
247/*
248 * munlock_vma_pages_range() - munlock all pages in the vma range.'
249 * @vma - vma containing range to be munlock()ed.
250 * @start - start address in @vma of the range
251 * @end - end of range in @vma.
252 *
253 * For mremap(), munmap() and exit().
254 *
255 * Called with @vma VM_LOCKED.
256 *
257 * Returns with VM_LOCKED cleared. Callers must be prepared to
258 * deal with this.
259 *
260 * We don't save and restore VM_LOCKED here because pages are
261 * still on lru. In unmap path, pages might be scanned by reclaim
262 * and re-mlocked by try_to_{munlock|unmap} before we unmap and
263 * free them. This will result in freeing mlocked pages.
264 */
265void munlock_vma_pages_range(struct vm_area_struct *vma,
266                 unsigned long start, unsigned long end)
267{
268    unsigned long addr;
269
270    lru_add_drain();
271    vma->vm_flags &= ~VM_LOCKED;
272
273    for (addr = start; addr < end; addr += PAGE_SIZE) {
274        struct page *page;
275        /*
276         * Although FOLL_DUMP is intended for get_dump_page(),
277         * it just so happens that its special treatment of the
278         * ZERO_PAGE (returning an error instead of doing get_page)
279         * suits munlock very well (and if somehow an abnormal page
280         * has sneaked into the range, we won't oops here: great).
281         */
282        page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
283        if (page && !IS_ERR(page)) {
284            lock_page(page);
285            /*
286             * Like in __mlock_vma_pages_range(),
287             * because we lock page here and migration is
288             * blocked by the elevated reference, we need
289             * only check for file-cache page truncation.
290             */
291            if (page->mapping)
292                munlock_vma_page(page);
293            unlock_page(page);
294            put_page(page);
295        }
296        cond_resched();
297    }
298}
299
300/*
301 * mlock_fixup - handle mlock[all]/munlock[all] requests.
302 *
303 * Filters out "special" vmas -- VM_LOCKED never gets set for these, and
304 * munlock is a no-op. However, for some special vmas, we go ahead and
305 * populate the ptes via make_pages_present().
306 *
307 * For vmas that pass the filters, merge/split as appropriate.
308 */
309static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
310    unsigned long start, unsigned long end, vm_flags_t newflags)
311{
312    struct mm_struct *mm = vma->vm_mm;
313    pgoff_t pgoff;
314    int nr_pages;
315    int ret = 0;
316    int lock = !!(newflags & VM_LOCKED);
317
318    if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) ||
319        is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm))
320        goto out; /* don't set VM_LOCKED, don't count */
321
322    pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
323    *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
324              vma->vm_file, pgoff, vma_policy(vma));
325    if (*prev) {
326        vma = *prev;
327        goto success;
328    }
329
330    if (start != vma->vm_start) {
331        ret = split_vma(mm, vma, start, 1);
332        if (ret)
333            goto out;
334    }
335
336    if (end != vma->vm_end) {
337        ret = split_vma(mm, vma, end, 0);
338        if (ret)
339            goto out;
340    }
341
342success:
343    /*
344     * Keep track of amount of locked VM.
345     */
346    nr_pages = (end - start) >> PAGE_SHIFT;
347    if (!lock)
348        nr_pages = -nr_pages;
349    mm->locked_vm += nr_pages;
350
351    /*
352     * vm_flags is protected by the mmap_sem held in write mode.
353     * It's okay if try_to_unmap_one unmaps a page just after we
354     * set VM_LOCKED, __mlock_vma_pages_range will bring it back.
355     */
356
357    if (lock)
358        vma->vm_flags = newflags;
359    else
360        munlock_vma_pages_range(vma, start, end);
361
362out:
363    *prev = vma;
364    return ret;
365}
366
367static int do_mlock(unsigned long start, size_t len, int on)
368{
369    unsigned long nstart, end, tmp;
370    struct vm_area_struct * vma, * prev;
371    int error;
372
373    VM_BUG_ON(start & ~PAGE_MASK);
374    VM_BUG_ON(len != PAGE_ALIGN(len));
375    end = start + len;
376    if (end < start)
377        return -EINVAL;
378    if (end == start)
379        return 0;
380    vma = find_vma_prev(current->mm, start, &prev);
381    if (!vma || vma->vm_start > start)
382        return -ENOMEM;
383
384    if (start > vma->vm_start)
385        prev = vma;
386
387    for (nstart = start ; ; ) {
388        vm_flags_t newflags;
389
390        /* Here we know that vma->vm_start <= nstart < vma->vm_end. */
391
392        newflags = vma->vm_flags | VM_LOCKED;
393        if (!on)
394            newflags &= ~VM_LOCKED;
395
396        tmp = vma->vm_end;
397        if (tmp > end)
398            tmp = end;
399        error = mlock_fixup(vma, &prev, nstart, tmp, newflags);
400        if (error)
401            break;
402        nstart = tmp;
403        if (nstart < prev->vm_end)
404            nstart = prev->vm_end;
405        if (nstart >= end)
406            break;
407
408        vma = prev->vm_next;
409        if (!vma || vma->vm_start != nstart) {
410            error = -ENOMEM;
411            break;
412        }
413    }
414    return error;
415}
416
417static int do_mlock_pages(unsigned long start, size_t len, int ignore_errors)
418{
419    struct mm_struct *mm = current->mm;
420    unsigned long end, nstart, nend;
421    struct vm_area_struct *vma = NULL;
422    int locked = 0;
423    int ret = 0;
424
425    VM_BUG_ON(start & ~PAGE_MASK);
426    VM_BUG_ON(len != PAGE_ALIGN(len));
427    end = start + len;
428
429    for (nstart = start; nstart < end; nstart = nend) {
430        /*
431         * We want to fault in pages for [nstart; end) address range.
432         * Find first corresponding VMA.
433         */
434        if (!locked) {
435            locked = 1;
436            down_read(&mm->mmap_sem);
437            vma = find_vma(mm, nstart);
438        } else if (nstart >= vma->vm_end)
439            vma = vma->vm_next;
440        if (!vma || vma->vm_start >= end)
441            break;
442        /*
443         * Set [nstart; nend) to intersection of desired address
444         * range with the first VMA. Also, skip undesirable VMA types.
445         */
446        nend = min(end, vma->vm_end);
447        if (vma->vm_flags & (VM_IO | VM_PFNMAP))
448            continue;
449        if (nstart < vma->vm_start)
450            nstart = vma->vm_start;
451        /*
452         * Now fault in a range of pages. __mlock_vma_pages_range()
453         * double checks the vma flags, so that it won't mlock pages
454         * if the vma was already munlocked.
455         */
456        ret = __mlock_vma_pages_range(vma, nstart, nend, &locked);
457        if (ret < 0) {
458            if (ignore_errors) {
459                ret = 0;
460                continue; /* continue at next VMA */
461            }
462            ret = __mlock_posix_error_return(ret);
463            break;
464        }
465        nend = nstart + ret * PAGE_SIZE;
466        ret = 0;
467    }
468    if (locked)
469        up_read(&mm->mmap_sem);
470    return ret; /* 0 or negative error code */
471}
472
473SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
474{
475    unsigned long locked;
476    unsigned long lock_limit;
477    int error = -ENOMEM;
478
479    if (!can_do_mlock())
480        return -EPERM;
481
482    lru_add_drain_all(); /* flush pagevec */
483
484    down_write(&current->mm->mmap_sem);
485    len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
486    start &= PAGE_MASK;
487
488    locked = len >> PAGE_SHIFT;
489    locked += current->mm->locked_vm;
490
491    lock_limit = rlimit(RLIMIT_MEMLOCK);
492    lock_limit >>= PAGE_SHIFT;
493
494    /* check against resource limits */
495    if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
496        error = do_mlock(start, len, 1);
497    up_write(&current->mm->mmap_sem);
498    if (!error)
499        error = do_mlock_pages(start, len, 0);
500    return error;
501}
502
503SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
504{
505    int ret;
506
507    down_write(&current->mm->mmap_sem);
508    len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
509    start &= PAGE_MASK;
510    ret = do_mlock(start, len, 0);
511    up_write(&current->mm->mmap_sem);
512    return ret;
513}
514
515static int do_mlockall(int flags)
516{
517    struct vm_area_struct * vma, * prev = NULL;
518    unsigned int def_flags = 0;
519
520    if (flags & MCL_FUTURE)
521        def_flags = VM_LOCKED;
522    current->mm->def_flags = def_flags;
523    if (flags == MCL_FUTURE)
524        goto out;
525
526    for (vma = current->mm->mmap; vma ; vma = prev->vm_next) {
527        vm_flags_t newflags;
528
529        newflags = vma->vm_flags | VM_LOCKED;
530        if (!(flags & MCL_CURRENT))
531            newflags &= ~VM_LOCKED;
532
533        /* Ignore errors */
534        mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
535    }
536out:
537    return 0;
538}
539
540SYSCALL_DEFINE1(mlockall, int, flags)
541{
542    unsigned long lock_limit;
543    int ret = -EINVAL;
544
545    if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE)))
546        goto out;
547
548    ret = -EPERM;
549    if (!can_do_mlock())
550        goto out;
551
552    lru_add_drain_all(); /* flush pagevec */
553
554    down_write(&current->mm->mmap_sem);
555
556    lock_limit = rlimit(RLIMIT_MEMLOCK);
557    lock_limit >>= PAGE_SHIFT;
558
559    ret = -ENOMEM;
560    if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
561        capable(CAP_IPC_LOCK))
562        ret = do_mlockall(flags);
563    up_write(&current->mm->mmap_sem);
564    if (!ret && (flags & MCL_CURRENT)) {
565        /* Ignore errors */
566        do_mlock_pages(0, TASK_SIZE, 1);
567    }
568out:
569    return ret;
570}
571
572SYSCALL_DEFINE0(munlockall)
573{
574    int ret;
575
576    down_write(&current->mm->mmap_sem);
577    ret = do_mlockall(0);
578    up_write(&current->mm->mmap_sem);
579    return ret;
580}
581
582/*
583 * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
584 * shm segments) get accounted against the user_struct instead.
585 */
586static DEFINE_SPINLOCK(shmlock_user_lock);
587
588int user_shm_lock(size_t size, struct user_struct *user)
589{
590    unsigned long lock_limit, locked;
591    int allowed = 0;
592
593    locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
594    lock_limit = rlimit(RLIMIT_MEMLOCK);
595    if (lock_limit == RLIM_INFINITY)
596        allowed = 1;
597    lock_limit >>= PAGE_SHIFT;
598    spin_lock(&shmlock_user_lock);
599    if (!allowed &&
600        locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))
601        goto out;
602    get_uid(user);
603    user->locked_shm += locked;
604    allowed = 1;
605out:
606    spin_unlock(&shmlock_user_lock);
607    return allowed;
608}
609
610void user_shm_unlock(size_t size, struct user_struct *user)
611{
612    spin_lock(&shmlock_user_lock);
613    user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
614    spin_unlock(&shmlock_user_lock);
615    free_uid(user);
616}
617

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