Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost

[cris-mirror.git] / mm / madvise.c

// SPDX-License-Identifier: GPL-2.0
/*
 *      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/userfaultfd_k.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>
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/shmem_fs.h>
#include <linux/mmu_notifier.h>

#include <asm/tlb.h>

#include "internal.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:
        case MADV_FREE:
                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_WIPEONFORK:
                /* MADV_WIPEONFORK is only supported on anonymous memory. */
                if (vma->vm_file || vma->vm_flags & VM_SHARED) {
                        error = -EINVAL;
                        goto out;
                }
                new_flags |= VM_WIPEONFORK;
                break;
        case MADV_KEEPONFORK:
                new_flags &= ~VM_WIPEONFORK;
                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) {
                        /*
                         * madvise() returns EAGAIN if kernel resources, such as
                         * slab, are temporarily unavailable.
                         */
                        if (error == -ENOMEM)
                                error = -EAGAIN;
                        goto out;
                }
                break;
        case MADV_HUGEPAGE:
        case MADV_NOHUGEPAGE:
                error = hugepage_madvise(vma, &new_flags, behavior);
                if (error) {
                        /*
                         * madvise() returns EAGAIN if kernel resources, such as
                         * slab, are temporarily unavailable.
                         */
                        if (error == -ENOMEM)
                                error = -EAGAIN;
                        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),
                          vma->vm_userfaultfd_ctx);
        if (*prev) {
                vma = *prev;
                goto success;
        }

        *prev = vma;

        if (start != vma->vm_start) {
                if (unlikely(mm->map_count >= sysctl_max_map_count)) {
                        error = -ENOMEM;
                        goto out;
                }
                error = __split_vma(mm, vma, start, 1);
                if (error) {
                        /*
                         * madvise() returns EAGAIN if kernel resources, such as
                         * slab, are temporarily unavailable.
                         */
                        if (error == -ENOMEM)
                                error = -EAGAIN;
                        goto out;
                }
        }

        if (end != vma->vm_end) {
                if (unlikely(mm->map_count >= sysctl_max_map_count)) {
                        error = -ENOMEM;
                        goto out;
                }
                error = __split_vma(mm, vma, end, 0);
                if (error) {
                        /*
                         * madvise() returns EAGAIN if kernel resources, such as
                         * slab, are temporarily unavailable.
                         */
                        if (error == -ENOMEM)
                                error = -EAGAIN;
                        goto out;
                }
        }

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

#ifdef CONFIG_SWAP
static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start,
        unsigned long end, struct mm_walk *walk)
{
        pte_t *orig_pte;
        struct vm_area_struct *vma = walk->private;
        unsigned long index;

        if (pmd_none_or_trans_huge_or_clear_bad(pmd))
                return 0;

        for (index = start; index != end; index += PAGE_SIZE) {
                pte_t pte;
                swp_entry_t entry;
                struct page *page;
                spinlock_t *ptl;

                orig_pte = pte_offset_map_lock(vma->vm_mm, pmd, start, &ptl);
                pte = *(orig_pte + ((index - start) / PAGE_SIZE));
                pte_unmap_unlock(orig_pte, ptl);

                if (pte_present(pte) || pte_none(pte))
                        continue;
                entry = pte_to_swp_entry(pte);
                if (unlikely(non_swap_entry(entry)))
                        continue;

                page = read_swap_cache_async(entry, GFP_HIGHUSER_MOVABLE,
                                                        vma, index, false);
                if (page)
                        put_page(page);
        }

        return 0;
}

static void force_swapin_readahead(struct vm_area_struct *vma,
                unsigned long start, unsigned long end)
{
        struct mm_walk walk = {
                .mm = vma->vm_mm,
                .pmd_entry = swapin_walk_pmd_entry,
                .private = vma,
        };

        walk_page_range(start, end, &walk);

        lru_add_drain();        /* Push any new pages onto the LRU now */
}

static void force_shm_swapin_readahead(struct vm_area_struct *vma,
                unsigned long start, unsigned long end,
                struct address_space *mapping)
{
        pgoff_t index;
        struct page *page;
        swp_entry_t swap;

        for (; start < end; start += PAGE_SIZE) {
                index = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;

                page = find_get_entry(mapping, index);
                if (!radix_tree_exceptional_entry(page)) {
                        if (page)
                                put_page(page);
                        continue;
                }
                swap = radix_to_swp_entry(page);
                page = read_swap_cache_async(swap, GFP_HIGHUSER_MOVABLE,
                                                        NULL, 0, false);
                if (page)
                        put_page(page);
        }

        lru_add_drain();        /* Push any new pages onto the LRU now */
}
#endif          /* CONFIG_SWAP */

/*
 * 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;

        *prev = vma;
#ifdef CONFIG_SWAP
        if (!file) {
                force_swapin_readahead(vma, start, end);
                return 0;
        }

        if (shmem_mapping(file->f_mapping)) {
                force_shm_swapin_readahead(vma, start, end,
                                        file->f_mapping);
                return 0;
        }
#else
        if (!file)
                return -EBADF;
#endif

        if (IS_DAX(file_inode(file))) {
                /* no bad return value, but ignore advice */
                return 0;
        }

        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;
}

static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
                                unsigned long end, struct mm_walk *walk)

{
        struct mmu_gather *tlb = walk->private;
        struct mm_struct *mm = tlb->mm;
        struct vm_area_struct *vma = walk->vma;
        spinlock_t *ptl;
        pte_t *orig_pte, *pte, ptent;
        struct page *page;
        int nr_swap = 0;
        unsigned long next;

        next = pmd_addr_end(addr, end);
        if (pmd_trans_huge(*pmd))
                if (madvise_free_huge_pmd(tlb, vma, pmd, addr, next))
                        goto next;

        if (pmd_trans_unstable(pmd))
                return 0;

        tlb_remove_check_page_size_change(tlb, PAGE_SIZE);
        orig_pte = pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
        flush_tlb_batched_pending(mm);
        arch_enter_lazy_mmu_mode();
        for (; addr != end; pte++, addr += PAGE_SIZE) {
                ptent = *pte;

                if (pte_none(ptent))
                        continue;
                /*
                 * If the pte has swp_entry, just clear page table to
                 * prevent swap-in which is more expensive rather than
                 * (page allocation + zeroing).
                 */
                if (!pte_present(ptent)) {
                        swp_entry_t entry;

                        entry = pte_to_swp_entry(ptent);
                        if (non_swap_entry(entry))
                                continue;
                        nr_swap--;
                        free_swap_and_cache(entry);
                        pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
                        continue;
                }

                page = _vm_normal_page(vma, addr, ptent, true);
                if (!page)
                        continue;

                /*
                 * If pmd isn't transhuge but the page is THP and
                 * is owned by only this process, split it and
                 * deactivate all pages.
                 */
                if (PageTransCompound(page)) {
                        if (page_mapcount(page) != 1)
                                goto out;
                        get_page(page);
                        if (!trylock_page(page)) {
                                put_page(page);
                                goto out;
                        }
                        pte_unmap_unlock(orig_pte, ptl);
                        if (split_huge_page(page)) {
                                unlock_page(page);
                                put_page(page);
                                pte_offset_map_lock(mm, pmd, addr, &ptl);
                                goto out;
                        }
                        unlock_page(page);
                        put_page(page);
                        pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
                        pte--;
                        addr -= PAGE_SIZE;
                        continue;
                }

                VM_BUG_ON_PAGE(PageTransCompound(page), page);

                if (PageSwapCache(page) || PageDirty(page)) {
                        if (!trylock_page(page))
                                continue;
                        /*
                         * If page is shared with others, we couldn't clear
                         * PG_dirty of the page.
                         */
                        if (page_mapcount(page) != 1) {
                                unlock_page(page);
                                continue;
                        }

                        if (PageSwapCache(page) && !try_to_free_swap(page)) {
                                unlock_page(page);
                                continue;
                        }

                        ClearPageDirty(page);
                        unlock_page(page);
                }

                if (pte_young(ptent) || pte_dirty(ptent)) {
                        /*
                         * Some of architecture(ex, PPC) don't update TLB
                         * with set_pte_at and tlb_remove_tlb_entry so for
                         * the portability, remap the pte with old|clean
                         * after pte clearing.
                         */
                        ptent = ptep_get_and_clear_full(mm, addr, pte,
                                                        tlb->fullmm);

                        ptent = pte_mkold(ptent);
                        ptent = pte_mkclean(ptent);
                        set_pte_at(mm, addr, pte, ptent);
                        tlb_remove_tlb_entry(tlb, pte, addr);
                }
                mark_page_lazyfree(page);
        }
out:
        if (nr_swap) {
                if (current->mm == mm)
                        sync_mm_rss(mm);

                add_mm_counter(mm, MM_SWAPENTS, nr_swap);
        }
        arch_leave_lazy_mmu_mode();
        pte_unmap_unlock(orig_pte, ptl);
        cond_resched();
next:
        return 0;
}

static void madvise_free_page_range(struct mmu_gather *tlb,
                             struct vm_area_struct *vma,
                             unsigned long addr, unsigned long end)
{
        struct mm_walk free_walk = {
                .pmd_entry = madvise_free_pte_range,
                .mm = vma->vm_mm,
                .private = tlb,
        };

        tlb_start_vma(tlb, vma);
        walk_page_range(addr, end, &free_walk);
        tlb_end_vma(tlb, vma);
}

static int madvise_free_single_vma(struct vm_area_struct *vma,
                        unsigned long start_addr, unsigned long end_addr)
{
        unsigned long start, end;
        struct mm_struct *mm = vma->vm_mm;
        struct mmu_gather tlb;

        /* MADV_FREE works for only anon vma at the moment */
        if (!vma_is_anonymous(vma))
                return -EINVAL;

        start = max(vma->vm_start, start_addr);
        if (start >= vma->vm_end)
                return -EINVAL;
        end = min(vma->vm_end, end_addr);
        if (end <= vma->vm_start)
                return -EINVAL;

        lru_add_drain();
        tlb_gather_mmu(&tlb, mm, start, end);
        update_hiwater_rss(mm);

        mmu_notifier_invalidate_range_start(mm, start, end);
        madvise_free_page_range(&tlb, vma, start, end);
        mmu_notifier_invalidate_range_end(mm, start, end);
        tlb_finish_mmu(&tlb, start, end);

        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_single_vma(struct vm_area_struct *vma,
                                        unsigned long start, unsigned long end)
{
        zap_page_range(vma, start, end - start);
        return 0;
}

static long madvise_dontneed_free(struct vm_area_struct *vma,
                                  struct vm_area_struct **prev,
                                  unsigned long start, unsigned long end,
                                  int behavior)
{
        *prev = vma;
        if (!can_madv_dontneed_vma(vma))
                return -EINVAL;

        if (!userfaultfd_remove(vma, start, end)) {
                *prev = NULL; /* mmap_sem has been dropped, prev is stale */

                down_read(&current->mm->mmap_sem);
                vma = find_vma(current->mm, start);
                if (!vma)
                        return -ENOMEM;
                if (start < vma->vm_start) {
                        /*
                         * This "vma" under revalidation is the one
                         * with the lowest vma->vm_start where start
                         * is also < vma->vm_end. If start <
                         * vma->vm_start it means an hole materialized
                         * in the user address space within the
                         * virtual range passed to MADV_DONTNEED
                         * or MADV_FREE.
                         */
                        return -ENOMEM;
                }
                if (!can_madv_dontneed_vma(vma))
                        return -EINVAL;
                if (end > vma->vm_end) {
                        /*
                         * Don't fail if end > vma->vm_end. If the old
                         * vma was splitted while the mmap_sem was
                         * released the effect of the concurrent
                         * operation may not cause madvise() to
                         * have an undefined result. There may be an
                         * adjacent next vma that we'll walk
                         * next. userfaultfd_remove() will generate an
                         * UFFD_EVENT_REMOVE repetition on the
                         * end-vma->vm_end range, but the manager can
                         * handle a repetition fine.
                         */
                        end = vma->vm_end;
                }
                VM_WARN_ON(start >= end);
        }

        if (behavior == MADV_DONTNEED)
                return madvise_dontneed_single_vma(vma, start, end);
        else if (behavior == MADV_FREE)
                return madvise_free_single_vma(vma, start, end);
        else
                return -EINVAL;
}

/*
 * Application wants to free up the pages and associated backing store.
 * This is effectively punching a hole into the middle of a file.
 */
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)
                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);
        if (userfaultfd_remove(vma, start, end)) {
                /* mmap_sem was not released by userfaultfd_remove() */
                up_read(&current->mm->mmap_sem);
        }
        error = vfs_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_inject_error(int behavior,
                unsigned long start, unsigned long end)
{
        struct page *page;
        struct zone *zone;
        unsigned int order;

        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;


        for (; start < end; start += PAGE_SIZE << order) {
                int ret;

                ret = get_user_pages_fast(start, 1, 0, &page);
                if (ret != 1)
                        return ret;

                /*
                 * When soft offlining hugepages, after migrating the page
                 * we dissolve it, therefore in the second loop "page" will
                 * no longer be a compound page, and order will be 0.
                 */
                order = compound_order(compound_head(page));

                if (PageHWPoison(page)) {
                        put_page(page);
                        continue;
                }

                if (behavior == MADV_SOFT_OFFLINE) {
                        pr_info("Soft offlining pfn %#lx at process virtual address %#lx\n",
                                                page_to_pfn(page), start);

                        ret = soft_offline_page(page, MF_COUNT_INCREASED);
                        if (ret)
                                return ret;
                        continue;
                }
                pr_info("Injecting memory failure for pfn %#lx at process virtual address %#lx\n",
                                                page_to_pfn(page), start);

                ret = memory_failure(page_to_pfn(page), MF_COUNT_INCREASED);
                if (ret)
                        return ret;
        }

        /* Ensure that all poisoned pages are removed from per-cpu lists */
        for_each_populated_zone(zone)
                drain_all_pages(zone);

        return 0;
}
#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_FREE:
        case MADV_DONTNEED:
                return madvise_dontneed_free(vma, prev, start, end, behavior);
        default:
                return madvise_behavior(vma, prev, start, end, behavior);
        }
}

static bool
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:
        case MADV_FREE:
#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:
        case MADV_WIPEONFORK:
        case MADV_KEEPONFORK:
#ifdef CONFIG_MEMORY_FAILURE
        case MADV_SOFT_OFFLINE:
        case MADV_HWPOISON:
#endif
                return true;

        default:
                return false;
        }
}

/*
 * 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_FREE - the application marks pages in the given range as lazy free,
 *              where actual purges are postponed until memory pressure happens.
 *  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_WIPEONFORK - present the child process with zero-filled memory in this
 *              range after a fork.
 *  MADV_KEEPONFORK - undo the effect of MADV_WIPEONFORK
 *  MADV_HWPOISON - trigger memory error handler as if the given memory range
 *              were corrupted by unrecoverable hardware memory failure.
 *  MADV_SOFT_OFFLINE - try to soft-offline the given range of memory.
 *  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.
 *  MADV_HUGEPAGE - the application wants to back the given range by transparent
 *              huge pages in the future. Existing pages might be coalesced and
 *              new pages might be allocated as THP.
 *  MADV_NOHUGEPAGE - mark the given range as not worth being backed by
 *              transparent huge pages so the existing pages will not be
 *              coalesced into THP and new pages will not be allocated as THP.
 *  MADV_DONTDUMP - the application wants to prevent pages in the given range
 *              from being included in its core dump.
 *  MADV_DODUMP - cancel MADV_DONTDUMP: no longer exclude from core dump.
 *
 * 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,
 *              or the specified address range includes file, Huge TLB,
 *              MAP_SHARED or VMPFNMAP range.
 *  -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;
        struct blk_plug plug;

        if (!madvise_behavior_valid(behavior))
                return error;

        if (start & ~PAGE_MASK)
                return error;
        len = (len_in + ~PAGE_MASK) & PAGE_MASK;

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

        end = start + len;
        if (end < start)
                return error;

        error = 0;
        if (end == start)
                return error;

#ifdef CONFIG_MEMORY_FAILURE
        if (behavior == MADV_HWPOISON || behavior == MADV_SOFT_OFFLINE)
                return madvise_inject_error(behavior, start, start + len_in);
#endif

        write = madvise_need_mmap_write(behavior);
        if (write) {
                if (down_write_killable(&current->mm->mmap_sem))
                        return -EINTR;
        } else {
                down_read(&current->mm->mmap_sem);
        }

        /*
         * 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;

        blk_start_plug(&plug);
        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:
        blk_finish_plug(&plug);
        if (write)
                up_write(&current->mm->mmap_sem);
        else
                up_read(&current->mm->mmap_sem);

        return error;
}