madvise.c

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/*
 *  linux/mm/madvise.c
 *
 * Copyright (C) 1999  Linus Torvalds
 * Copyright (C) 2002  Christoph Hellwig
 */

#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/syscalls.h>
#include <linux/mempolicy.h>
#include <linux/page-isolation.h>
#include <linux/hugetlb.h>
#include <linux/falloc.h>
#include <linux/sched.h>
#include <linux/ksm.h>
#include <linux/fs.h>
#include <linux/file.h>

/*
 * Any behaviour which results in changes to the vma->vm_flags needs to
 * take mmap_sem for writing. Others, which simply traverse vmas, need
 * to only take it for reading.
 */
static int madvise_need_mmap_write(int behavior)
{
    switch (behavior) {
    case MADV_REMOVE:
    case MADV_WILLNEED:
    case MADV_DONTNEED:
        return 0;
    default:
        /* be safe, default to 1. list exceptions explicitly */
        return 1;
    }
}

/*
 * We can potentially split a vm area into separate
 * areas, each area with its own behavior.
 */
static long madvise_behavior(struct vm_area_struct * vma,
             struct vm_area_struct **prev,
             unsigned long start, unsigned long end, int behavior)
{
    struct mm_struct * mm = vma->vm_mm;
    int error = 0;
    pgoff_t pgoff;
    unsigned long new_flags = vma->vm_flags;

    switch (behavior) {
    case MADV_NORMAL:
        new_flags = new_flags & ~VM_RAND_READ & ~VM_SEQ_READ;
        break;
    case MADV_SEQUENTIAL:
        new_flags = (new_flags & ~VM_RAND_READ) | VM_SEQ_READ;
        break;
    case MADV_RANDOM:
        new_flags = (new_flags & ~VM_SEQ_READ) | VM_RAND_READ;
        break;
    case MADV_DONTFORK:
        new_flags |= VM_DONTCOPY;
        break;
    case MADV_DOFORK:
        if (vma->vm_flags & VM_IO) {
            error = -EINVAL;
            goto out;
        }
        new_flags &= ~VM_DONTCOPY;
        break;
    case MADV_DONTDUMP:
        new_flags |= VM_DONTDUMP;
        break;
    case MADV_DODUMP:
        if (new_flags & VM_SPECIAL) {
            error = -EINVAL;
            goto out;
        }
        new_flags &= ~VM_DONTDUMP;
        break;
    case MADV_MERGEABLE:
    case MADV_UNMERGEABLE:
        error = ksm_madvise(vma, start, end, behavior, &new_flags);
        if (error)
            goto out;
        break;
    case MADV_HUGEPAGE:
    case MADV_NOHUGEPAGE:
        error = hugepage_madvise(vma, &new_flags, behavior);
        if (error)
            goto out;
        break;
    }

    if (new_flags == vma->vm_flags) {
        *prev = vma;
        goto out;
    }

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

    *prev = vma;

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

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

success:
    /*
     * vm_flags is protected by the mmap_sem held in write mode.
     */
    vma->vm_flags = new_flags;

out:
    if (error == -ENOMEM)
        error = -EAGAIN;
    return error;
}

/*
 * Schedule all required I/O operations.  Do not wait for completion.
 */
static long madvise_willneed(struct vm_area_struct * vma,
                 struct vm_area_struct ** prev,
                 unsigned long start, unsigned long end)
{
    struct file *file = vma->vm_file;

    if (!file)
        return -EBADF;

    if (file->f_mapping->a_ops->get_xip_mem) {
        /* no bad return value, but ignore advice */
        return 0;
    }

    *prev = vma;
    start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
    if (end > vma->vm_end)
        end = vma->vm_end;
    end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;

    force_page_cache_readahead(file->f_mapping, file, start, end - start);
    return 0;
}

/*
 * Application no longer needs these pages.  If the pages are dirty,
 * it's OK to just throw them away.  The app will be more careful about
 * data it wants to keep.  Be sure to free swap resources too.  The
 * zap_page_range call sets things up for shrink_active_list to actually free
 * these pages later if no one else has touched them in the meantime,
 * although we could add these pages to a global reuse list for
 * shrink_active_list to pick up before reclaiming other pages.
 *
 * NB: This interface discards data rather than pushes it out to swap,
 * as some implementations do.  This has performance implications for
 * applications like large transactional databases which want to discard
 * pages in anonymous maps after committing to backing store the data
 * that was kept in them.  There is no reason to write this data out to
 * the swap area if the application is discarding it.
 *
 * An interface that causes the system to free clean pages and flush
 * dirty pages is already available as msync(MS_INVALIDATE).
 */
static long madvise_dontneed(struct vm_area_struct * vma,
                 struct vm_area_struct ** prev,
                 unsigned long start, unsigned long end)
{
    *prev = vma;
    if (vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP))
        return -EINVAL;

    if (unlikely(vma->vm_flags & VM_NONLINEAR)) {
        struct zap_details details = {
            .nonlinear_vma = vma,
            .last_index = ULONG_MAX,
        };
        zap_page_range(vma, start, end - start, &details);
    } else
        zap_page_range(vma, start, end - start, NULL);
    return 0;
}

/*
 * Application wants to free up the pages and associated backing store.
 * This is effectively punching a hole into the middle of a file.
 *
 * NOTE: Currently, only shmfs/tmpfs is supported for this operation.
 * Other filesystems return -ENOSYS.
 */
static long madvise_remove(struct vm_area_struct *vma,
                struct vm_area_struct **prev,
                unsigned long start, unsigned long end)
{
    loff_t offset;
    int error;
    struct file *f;

    *prev = NULL;   /* tell sys_madvise we drop mmap_sem */

    if (vma->vm_flags & (VM_LOCKED|VM_NONLINEAR|VM_HUGETLB))
        return -EINVAL;

    f = vma->vm_file;

    if (!f || !f->f_mapping || !f->f_mapping->host) {
            return -EINVAL;
    }

    if ((vma->vm_flags & (VM_SHARED|VM_WRITE)) != (VM_SHARED|VM_WRITE))
        return -EACCES;

    offset = (loff_t)(start - vma->vm_start)
            + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);

    /*
     * Filesystem's fallocate may need to take i_mutex.  We need to
     * explicitly grab a reference because the vma (and hence the
     * vma's reference to the file) can go away as soon as we drop
     * mmap_sem.
     */
    get_file(f);
    up_read(&current->mm->mmap_sem);
    error = do_fallocate(f,
                FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
                offset, end - start);
    fput(f);
    down_read(&current->mm->mmap_sem);
    return error;
}

#ifdef CONFIG_MEMORY_FAILURE
/*
 * Error injection support for memory error handling.
 */
static int madvise_hwpoison(int bhv, unsigned long start, unsigned long end)
{
    int ret = 0;

    if (!capable(CAP_SYS_ADMIN))
        return -EPERM;
    for (; start < end; start += PAGE_SIZE) {
        struct page *p;
        int ret = get_user_pages_fast(start, 1, 0, &p);
        if (ret != 1)
            return ret;
        if (bhv == MADV_SOFT_OFFLINE) {
            printk(KERN_INFO "Soft offlining page %lx at %lx\n",
                page_to_pfn(p), start);
            ret = soft_offline_page(p, MF_COUNT_INCREASED);
            if (ret)
                break;
            continue;
        }
        printk(KERN_INFO "Injecting memory failure for page %lx at %lx\n",
               page_to_pfn(p), start);
        /* Ignore return value for now */
        memory_failure(page_to_pfn(p), 0, MF_COUNT_INCREASED);
    }
    return ret;
}
#endif

static long
madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
        unsigned long start, unsigned long end, int behavior)
{
    switch (behavior) {
    case MADV_REMOVE:
        return madvise_remove(vma, prev, start, end);
    case MADV_WILLNEED:
        return madvise_willneed(vma, prev, start, end);
    case MADV_DONTNEED:
        return madvise_dontneed(vma, prev, start, end);
    default:
        return madvise_behavior(vma, prev, start, end, behavior);
    }
}

static int
madvise_behavior_valid(int behavior)
{
    switch (behavior) {
    case MADV_DOFORK:
    case MADV_DONTFORK:
    case MADV_NORMAL:
    case MADV_SEQUENTIAL:
    case MADV_RANDOM:
    case MADV_REMOVE:
    case MADV_WILLNEED:
    case MADV_DONTNEED:
#ifdef CONFIG_KSM
    case MADV_MERGEABLE:
    case MADV_UNMERGEABLE:
#endif
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
    case MADV_HUGEPAGE:
    case MADV_NOHUGEPAGE:
#endif
    case MADV_DONTDUMP:
    case MADV_DODUMP:
        return 1;

    default:
        return 0;
    }
}

/*
 * The madvise(2) system call.
 *
 * Applications can use madvise() to advise the kernel how it should
 * handle paging I/O in this VM area.  The idea is to help the kernel
 * use appropriate read-ahead and caching techniques.  The information
 * provided is advisory only, and can be safely disregarded by the
 * kernel without affecting the correct operation of the application.
 *
 * behavior values:
 *  MADV_NORMAL - the default behavior is to read clusters.  This
 *      results in some read-ahead and read-behind.
 *  MADV_RANDOM - the system should read the minimum amount of data
 *      on any access, since it is unlikely that the appli-
 *      cation will need more than what it asks for.
 *  MADV_SEQUENTIAL - pages in the given range will probably be accessed
 *      once, so they can be aggressively read ahead, and
 *      can be freed soon after they are accessed.
 *  MADV_WILLNEED - the application is notifying the system to read
 *      some pages ahead.
 *  MADV_DONTNEED - the application is finished with the given range,
 *      so the kernel can free resources associated with it.
 *  MADV_REMOVE - the application wants to free up the given range of
 *      pages and associated backing store.
 *  MADV_DONTFORK - omit this area from child's address space when forking:
 *      typically, to avoid COWing pages pinned by get_user_pages().
 *  MADV_DOFORK - cancel MADV_DONTFORK: no longer omit this area when forking.
 *  MADV_MERGEABLE - the application recommends that KSM try to merge pages in
 *      this area with pages of identical content from other such areas.
 *  MADV_UNMERGEABLE- cancel MADV_MERGEABLE: no longer merge pages with others.
 *
 * return values:
 *  zero    - success
 *  -EINVAL - start + len < 0, start is not page-aligned,
 *      "behavior" is not a valid value, or application
 *      is attempting to release locked or shared pages.
 *  -ENOMEM - addresses in the specified range are not currently
 *      mapped, or are outside the AS of the process.
 *  -EIO    - an I/O error occurred while paging in data.
 *  -EBADF  - map exists, but area maps something that isn't a file.
 *  -EAGAIN - a kernel resource was temporarily unavailable.
 */
SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
{
    unsigned long end, tmp;
    struct vm_area_struct * vma, *prev;
    int unmapped_error = 0;
    int error = -EINVAL;
    int write;
    size_t len;

#ifdef CONFIG_MEMORY_FAILURE
    if (behavior == MADV_HWPOISON || behavior == MADV_SOFT_OFFLINE)
        return madvise_hwpoison(behavior, start, start+len_in);
#endif
    if (!madvise_behavior_valid(behavior))
        return error;

    write = madvise_need_mmap_write(behavior);
    if (write)
        down_write(&current->mm->mmap_sem);
    else
        down_read(&current->mm->mmap_sem);

    if (start & ~PAGE_MASK)
        goto out;
    len = (len_in + ~PAGE_MASK) & PAGE_MASK;

    /* Check to see whether len was rounded up from small -ve to zero */
    if (len_in && !len)
        goto out;

    end = start + len;
    if (end < start)
        goto out;

    error = 0;
    if (end == start)
        goto out;

    /*
     * If the interval [start,end) covers some unmapped address
     * ranges, just ignore them, but return -ENOMEM at the end.
     * - different from the way of handling in mlock etc.
     */
    vma = find_vma_prev(current->mm, start, &prev);
    if (vma && start > vma->vm_start)
        prev = vma;

    for (;;) {
        /* Still start < end. */
        error = -ENOMEM;
        if (!vma)
            goto out;

        /* Here start < (end|vma->vm_end). */
        if (start < vma->vm_start) {
            unmapped_error = -ENOMEM;
            start = vma->vm_start;
            if (start >= end)
                goto out;
        }

        /* Here vma->vm_start <= start < (end|vma->vm_end) */
        tmp = vma->vm_end;
        if (end < tmp)
            tmp = end;

        /* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
        error = madvise_vma(vma, &prev, start, tmp, behavior);
        if (error)
            goto out;
        start = tmp;
        if (prev && start < prev->vm_end)
            start = prev->vm_end;
        error = unmapped_error;
        if (start >= end)
            goto out;
        if (prev)
            vma = prev->vm_next;
        else    /* madvise_remove dropped mmap_sem */
            vma = find_vma(current->mm, start);
    }
out:
    if (write)
        up_write(&current->mm->mmap_sem);
    else
        up_read(&current->mm->mmap_sem);

    return error;
}