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{
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 */
232static 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 */
254long 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
286no_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 */
309void 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 */
353static 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
394success:
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
418out:
419    *prev = vma;
420    return ret;
421}
422
423static 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
472SYSCALL_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 = rlimit(RLIMIT_MEMLOCK);
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
500SYSCALL_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
512static 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    }
533out:
534    return 0;
535}
536
537SYSCALL_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 = rlimit(RLIMIT_MEMLOCK);
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);
561out:
562    return ret;
563}
564
565SYSCALL_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 */
579static DEFINE_SPINLOCK(shmlock_user_lock);
580
581int 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 = rlimit(RLIMIT_MEMLOCK);
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;
598out:
599    spin_unlock(&shmlock_user_lock);
600    return allowed;
601}
602
603void 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

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