mlock.c

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/*
 *  linux/mm/mlock.c
 *
 *  (C) Copyright 1995 Linus Torvalds
 *  (C) Copyright 2002 Christoph Hellwig
 */

#include <linux/capability.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/pagemap.h>
#include <linux/mempolicy.h>
#include <linux/syscalls.h>
#include <linux/sched.h>
#include <linux/export.h>
#include <linux/rmap.h>
#include <linux/mmzone.h>
#include <linux/hugetlb.h>

#include "internal.h"

int can_do_mlock(void)
{
    if (capable(CAP_IPC_LOCK))
        return 1;
    if (rlimit(RLIMIT_MEMLOCK) != 0)
        return 1;
    return 0;
}
EXPORT_SYMBOL(can_do_mlock);

/*
 * Mlocked pages are marked with PageMlocked() flag for efficient testing
 * in vmscan and, possibly, the fault path; and to support semi-accurate
 * statistics.
 *
 * An mlocked page [PageMlocked(page)] is unevictable.  As such, it will
 * be placed on the LRU "unevictable" list, rather than the [in]active lists.
 * The unevictable list is an LRU sibling list to the [in]active lists.
 * PageUnevictable is set to indicate the unevictable state.
 *
 * When lazy mlocking via vmscan, it is important to ensure that the
 * vma's VM_LOCKED status is not concurrently being modified, otherwise we
 * may have mlocked a page that is being munlocked. So lazy mlock must take
 * the mmap_sem for read, and verify that the vma really is locked
 * (see mm/rmap.c).
 */

/*
 *  LRU accounting for clear_page_mlock()
 */
void clear_page_mlock(struct page *page)
{
    if (!TestClearPageMlocked(page))
        return;

    mod_zone_page_state(page_zone(page), NR_MLOCK,
                -hpage_nr_pages(page));
    count_vm_event(UNEVICTABLE_PGCLEARED);
    if (!isolate_lru_page(page)) {
        putback_lru_page(page);
    } else {
        /*
         * We lost the race. the page already moved to evictable list.
         */
        if (PageUnevictable(page))
            count_vm_event(UNEVICTABLE_PGSTRANDED);
    }
}

/*
 * Mark page as mlocked if not already.
 * If page on LRU, isolate and putback to move to unevictable list.
 */
void mlock_vma_page(struct page *page)
{
    BUG_ON(!PageLocked(page));

    if (!TestSetPageMlocked(page)) {
        mod_zone_page_state(page_zone(page), NR_MLOCK,
                    hpage_nr_pages(page));
        count_vm_event(UNEVICTABLE_PGMLOCKED);
        if (!isolate_lru_page(page))
            putback_lru_page(page);
    }
}

void munlock_vma_page(struct page *page)
{
    BUG_ON(!PageLocked(page));

    if (TestClearPageMlocked(page)) {
        mod_zone_page_state(page_zone(page), NR_MLOCK,
                    -hpage_nr_pages(page));
        if (!isolate_lru_page(page)) {
            int ret = SWAP_AGAIN;

            /*
             * Optimization: if the page was mapped just once,
             * that's our mapping and we don't need to check all the
             * other vmas.
             */
            if (page_mapcount(page) > 1)
                ret = try_to_munlock(page);
            /*
             * did try_to_unlock() succeed or punt?
             */
            if (ret != SWAP_MLOCK)
                count_vm_event(UNEVICTABLE_PGMUNLOCKED);

            putback_lru_page(page);
        } else {
            /*
             * Some other task has removed the page from the LRU.
             * putback_lru_page() will take care of removing the
             * page from the unevictable list, if necessary.
             * vmscan [page_referenced()] will move the page back
             * to the unevictable list if some other vma has it
             * mlocked.
             */
            if (PageUnevictable(page))
                count_vm_event(UNEVICTABLE_PGSTRANDED);
            else
                count_vm_event(UNEVICTABLE_PGMUNLOCKED);
        }
    }
}

static long __mlock_vma_pages_range(struct vm_area_struct *vma,
                    unsigned long start, unsigned long end,
                    int *nonblocking)
{
    struct mm_struct *mm = vma->vm_mm;
    unsigned long addr = start;
    int nr_pages = (end - start) / PAGE_SIZE;
    int gup_flags;

    VM_BUG_ON(start & ~PAGE_MASK);
    VM_BUG_ON(end   & ~PAGE_MASK);
    VM_BUG_ON(start < vma->vm_start);
    VM_BUG_ON(end   > vma->vm_end);
    VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));

    gup_flags = FOLL_TOUCH | FOLL_MLOCK;
    /*
     * We want to touch writable mappings with a write fault in order
     * to break COW, except for shared mappings because these don't COW
     * and we would not want to dirty them for nothing.
     */
    if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
        gup_flags |= FOLL_WRITE;

    /*
     * We want mlock to succeed for regions that have any permissions
     * other than PROT_NONE.
     */
    if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC))
        gup_flags |= FOLL_FORCE;

    return __get_user_pages(current, mm, addr, nr_pages, gup_flags,
                NULL, NULL, nonblocking);
}

/*
 * convert get_user_pages() return value to posix mlock() error
 */
static int __mlock_posix_error_return(long retval)
{
    if (retval == -EFAULT)
        retval = -ENOMEM;
    else if (retval == -ENOMEM)
        retval = -EAGAIN;
    return retval;
}

long mlock_vma_pages_range(struct vm_area_struct *vma,
            unsigned long start, unsigned long end)
{
    int nr_pages = (end - start) / PAGE_SIZE;
    BUG_ON(!(vma->vm_flags & VM_LOCKED));

    /*
     * filter unlockable vmas
     */
    if (vma->vm_flags & (VM_IO | VM_PFNMAP))
        goto no_mlock;

    if (!((vma->vm_flags & VM_DONTEXPAND) ||
            is_vm_hugetlb_page(vma) ||
            vma == get_gate_vma(current->mm))) {

        __mlock_vma_pages_range(vma, start, end, NULL);

        /* Hide errors from mmap() and other callers */
        return 0;
    }

    /*
     * User mapped kernel pages or huge pages:
     * make these pages present to populate the ptes, but
     * fall thru' to reset VM_LOCKED--no need to unlock, and
     * return nr_pages so these don't get counted against task's
     * locked limit.  huge pages are already counted against
     * locked vm limit.
     */
    make_pages_present(start, end);

no_mlock:
    vma->vm_flags &= ~VM_LOCKED;    /* and don't come back! */
    return nr_pages;        /* error or pages NOT mlocked */
}

/*
 * munlock_vma_pages_range() - munlock all pages in the vma range.'
 * @vma - vma containing range to be munlock()ed.
 * @start - start address in @vma of the range
 * @end - end of range in @vma.
 *
 *  For mremap(), munmap() and exit().
 *
 * Called with @vma VM_LOCKED.
 *
 * Returns with VM_LOCKED cleared.  Callers must be prepared to
 * deal with this.
 *
 * We don't save and restore VM_LOCKED here because pages are
 * still on lru.  In unmap path, pages might be scanned by reclaim
 * and re-mlocked by try_to_{munlock|unmap} before we unmap and
 * free them.  This will result in freeing mlocked pages.
 */
void munlock_vma_pages_range(struct vm_area_struct *vma,
                 unsigned long start, unsigned long end)
{
    unsigned long addr;

    lru_add_drain();
    vma->vm_flags &= ~VM_LOCKED;

    for (addr = start; addr < end; addr += PAGE_SIZE) {
        struct page *page;
        /*
         * Although FOLL_DUMP is intended for get_dump_page(),
         * it just so happens that its special treatment of the
         * ZERO_PAGE (returning an error instead of doing get_page)
         * suits munlock very well (and if somehow an abnormal page
         * has sneaked into the range, we won't oops here: great).
         */
        page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
        if (page && !IS_ERR(page)) {
            lock_page(page);
            munlock_vma_page(page);
            unlock_page(page);
            put_page(page);
        }
        cond_resched();
    }
}

/*
 * mlock_fixup  - handle mlock[all]/munlock[all] requests.
 *
 * Filters out "special" vmas -- VM_LOCKED never gets set for these, and
 * munlock is a no-op.  However, for some special vmas, we go ahead and
 * populate the ptes via make_pages_present().
 *
 * For vmas that pass the filters, merge/split as appropriate.
 */
static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
    unsigned long start, unsigned long end, vm_flags_t newflags)
{
    struct mm_struct *mm = vma->vm_mm;
    pgoff_t pgoff;
    int nr_pages;
    int ret = 0;
    int lock = !!(newflags & VM_LOCKED);

    if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) ||
        is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm))
        goto out;   /* don't set VM_LOCKED,  don't count */

    pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
    *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
              vma->vm_file, pgoff, vma_policy(vma));
    if (*prev) {
        vma = *prev;
        goto success;
    }

    if (start != vma->vm_start) {
        ret = split_vma(mm, vma, start, 1);
        if (ret)
            goto out;
    }

    if (end != vma->vm_end) {
        ret = split_vma(mm, vma, end, 0);
        if (ret)
            goto out;
    }

success:
    /*
     * Keep track of amount of locked VM.
     */
    nr_pages = (end - start) >> PAGE_SHIFT;
    if (!lock)
        nr_pages = -nr_pages;
    mm->locked_vm += nr_pages;

    /*
     * vm_flags is protected by the mmap_sem held in write mode.
     * It's okay if try_to_unmap_one unmaps a page just after we
     * set VM_LOCKED, __mlock_vma_pages_range will bring it back.
     */

    if (lock)
        vma->vm_flags = newflags;
    else
        munlock_vma_pages_range(vma, start, end);

out:
    *prev = vma;
    return ret;
}

static int do_mlock(unsigned long start, size_t len, int on)
{
    unsigned long nstart, end, tmp;
    struct vm_area_struct * vma, * prev;
    int error;

    VM_BUG_ON(start & ~PAGE_MASK);
    VM_BUG_ON(len != PAGE_ALIGN(len));
    end = start + len;
    if (end < start)
        return -EINVAL;
    if (end == start)
        return 0;
    vma = find_vma(current->mm, start);
    if (!vma || vma->vm_start > start)
        return -ENOMEM;

    prev = vma->vm_prev;
    if (start > vma->vm_start)
        prev = vma;

    for (nstart = start ; ; ) {
        vm_flags_t newflags;

        /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */

        newflags = vma->vm_flags | VM_LOCKED;
        if (!on)
            newflags &= ~VM_LOCKED;

        tmp = vma->vm_end;
        if (tmp > end)
            tmp = end;
        error = mlock_fixup(vma, &prev, nstart, tmp, newflags);
        if (error)
            break;
        nstart = tmp;
        if (nstart < prev->vm_end)
            nstart = prev->vm_end;
        if (nstart >= end)
            break;

        vma = prev->vm_next;
        if (!vma || vma->vm_start != nstart) {
            error = -ENOMEM;
            break;
        }
    }
    return error;
}

static int do_mlock_pages(unsigned long start, size_t len, int ignore_errors)
{
    struct mm_struct *mm = current->mm;
    unsigned long end, nstart, nend;
    struct vm_area_struct *vma = NULL;
    int locked = 0;
    int ret = 0;

    VM_BUG_ON(start & ~PAGE_MASK);
    VM_BUG_ON(len != PAGE_ALIGN(len));
    end = start + len;

    for (nstart = start; nstart < end; nstart = nend) {
        /*
         * We want to fault in pages for [nstart; end) address range.
         * Find first corresponding VMA.
         */
        if (!locked) {
            locked = 1;
            down_read(&mm->mmap_sem);
            vma = find_vma(mm, nstart);
        } else if (nstart >= vma->vm_end)
            vma = vma->vm_next;
        if (!vma || vma->vm_start >= end)
            break;
        /*
         * Set [nstart; nend) to intersection of desired address
         * range with the first VMA. Also, skip undesirable VMA types.
         */
        nend = min(end, vma->vm_end);
        if (vma->vm_flags & (VM_IO | VM_PFNMAP))
            continue;
        if (nstart < vma->vm_start)
            nstart = vma->vm_start;
        /*
         * Now fault in a range of pages. __mlock_vma_pages_range()
         * double checks the vma flags, so that it won't mlock pages
         * if the vma was already munlocked.
         */
        ret = __mlock_vma_pages_range(vma, nstart, nend, &locked);
        if (ret < 0) {
            if (ignore_errors) {
                ret = 0;
                continue;   /* continue at next VMA */
            }
            ret = __mlock_posix_error_return(ret);
            break;
        }
        nend = nstart + ret * PAGE_SIZE;
        ret = 0;
    }
    if (locked)
        up_read(&mm->mmap_sem);
    return ret; /* 0 or negative error code */
}

SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
{
    unsigned long locked;
    unsigned long lock_limit;
    int error = -ENOMEM;

    if (!can_do_mlock())
        return -EPERM;

    lru_add_drain_all();    /* flush pagevec */

    down_write(&current->mm->mmap_sem);
    len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
    start &= PAGE_MASK;

    locked = len >> PAGE_SHIFT;
    locked += current->mm->locked_vm;

    lock_limit = rlimit(RLIMIT_MEMLOCK);
    lock_limit >>= PAGE_SHIFT;

    /* check against resource limits */
    if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
        error = do_mlock(start, len, 1);
    up_write(&current->mm->mmap_sem);
    if (!error)
        error = do_mlock_pages(start, len, 0);
    return error;
}

SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
{
    int ret;

    down_write(&current->mm->mmap_sem);
    len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
    start &= PAGE_MASK;
    ret = do_mlock(start, len, 0);
    up_write(&current->mm->mmap_sem);
    return ret;
}

static int do_mlockall(int flags)
{
    struct vm_area_struct * vma, * prev = NULL;
    unsigned int def_flags = 0;

    if (flags & MCL_FUTURE)
        def_flags = VM_LOCKED;
    current->mm->def_flags = def_flags;
    if (flags == MCL_FUTURE)
        goto out;

    for (vma = current->mm->mmap; vma ; vma = prev->vm_next) {
        vm_flags_t newflags;

        newflags = vma->vm_flags | VM_LOCKED;
        if (!(flags & MCL_CURRENT))
            newflags &= ~VM_LOCKED;

        /* Ignore errors */
        mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
    }
out:
    return 0;
}

SYSCALL_DEFINE1(mlockall, int, flags)
{
    unsigned long lock_limit;
    int ret = -EINVAL;

    if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE)))
        goto out;

    ret = -EPERM;
    if (!can_do_mlock())
        goto out;

    if (flags & MCL_CURRENT)
        lru_add_drain_all();    /* flush pagevec */

    down_write(&current->mm->mmap_sem);

    lock_limit = rlimit(RLIMIT_MEMLOCK);
    lock_limit >>= PAGE_SHIFT;

    ret = -ENOMEM;
    if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
        capable(CAP_IPC_LOCK))
        ret = do_mlockall(flags);
    up_write(&current->mm->mmap_sem);
    if (!ret && (flags & MCL_CURRENT)) {
        /* Ignore errors */
        do_mlock_pages(0, TASK_SIZE, 1);
    }
out:
    return ret;
}

SYSCALL_DEFINE0(munlockall)
{
    int ret;

    down_write(&current->mm->mmap_sem);
    ret = do_mlockall(0);
    up_write(&current->mm->mmap_sem);
    return ret;
}

/*
 * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
 * shm segments) get accounted against the user_struct instead.
 */
static DEFINE_SPINLOCK(shmlock_user_lock);

int user_shm_lock(size_t size, struct user_struct *user)
{
    unsigned long lock_limit, locked;
    int allowed = 0;

    locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
    lock_limit = rlimit(RLIMIT_MEMLOCK);
    if (lock_limit == RLIM_INFINITY)
        allowed = 1;
    lock_limit >>= PAGE_SHIFT;
    spin_lock(&shmlock_user_lock);
    if (!allowed &&
        locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))
        goto out;
    get_uid(user);
    user->locked_shm += locked;
    allowed = 1;
out:
    spin_unlock(&shmlock_user_lock);
    return allowed;
}

void user_shm_unlock(size_t size, struct user_struct *user)
{
    spin_lock(&shmlock_user_lock);
    user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
    spin_unlock(&shmlock_user_lock);
    free_uid(user);
}