mremap.c

Go to the documentation of this file.

/*
 *  mm/mremap.c
 *
 *  (C) Copyright 1996 Linus Torvalds
 *
 *  Address space accounting code   <[email protected]>
 *  (C) Copyright 2002 Red Hat Inc, All Rights Reserved
 */

#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <linux/shm.h>
#include <linux/ksm.h>
#include <linux/mman.h>
#include <linux/swap.h>
#include <linux/capability.h>
#include <linux/fs.h>
#include <linux/highmem.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/mmu_notifier.h>

#include <asm/uaccess.h>
#include <asm/cacheflush.h>
#include <asm/tlbflush.h>

#include "internal.h"

static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
{
    pgd_t *pgd;
    pud_t *pud;
    pmd_t *pmd;

    pgd = pgd_offset(mm, addr);
    if (pgd_none_or_clear_bad(pgd))
        return NULL;

    pud = pud_offset(pgd, addr);
    if (pud_none_or_clear_bad(pud))
        return NULL;

    pmd = pmd_offset(pud, addr);
    if (pmd_none(*pmd))
        return NULL;

    return pmd;
}

static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
                unsigned long addr)
{
    pgd_t *pgd;
    pud_t *pud;
    pmd_t *pmd;

    pgd = pgd_offset(mm, addr);
    pud = pud_alloc(mm, pgd, addr);
    if (!pud)
        return NULL;

    pmd = pmd_alloc(mm, pud, addr);
    if (!pmd)
        return NULL;

    VM_BUG_ON(pmd_trans_huge(*pmd));

    return pmd;
}

static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
        unsigned long old_addr, unsigned long old_end,
        struct vm_area_struct *new_vma, pmd_t *new_pmd,
        unsigned long new_addr, bool need_rmap_locks)
{
    struct address_space *mapping = NULL;
    struct anon_vma *anon_vma = NULL;
    struct mm_struct *mm = vma->vm_mm;
    pte_t *old_pte, *new_pte, pte;
    spinlock_t *old_ptl, *new_ptl;

    /*
     * When need_rmap_locks is true, we take the i_mmap_mutex and anon_vma
     * locks to ensure that rmap will always observe either the old or the
     * new ptes. This is the easiest way to avoid races with
     * truncate_pagecache(), page migration, etc...
     *
     * When need_rmap_locks is false, we use other ways to avoid
     * such races:
     *
     * - During exec() shift_arg_pages(), we use a specially tagged vma
     *   which rmap call sites look for using is_vma_temporary_stack().
     *
     * - During mremap(), new_vma is often known to be placed after vma
     *   in rmap traversal order. This ensures rmap will always observe
     *   either the old pte, or the new pte, or both (the page table locks
     *   serialize access to individual ptes, but only rmap traversal
     *   order guarantees that we won't miss both the old and new ptes).
     */
    if (need_rmap_locks) {
        if (vma->vm_file) {
            mapping = vma->vm_file->f_mapping;
            mutex_lock(&mapping->i_mmap_mutex);
        }
        if (vma->anon_vma) {
            anon_vma = vma->anon_vma;
            anon_vma_lock(anon_vma);
        }
    }

    /*
     * We don't have to worry about the ordering of src and dst
     * pte locks because exclusive mmap_sem prevents deadlock.
     */
    old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
    new_pte = pte_offset_map(new_pmd, new_addr);
    new_ptl = pte_lockptr(mm, new_pmd);
    if (new_ptl != old_ptl)
        spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
    arch_enter_lazy_mmu_mode();

    for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
                   new_pte++, new_addr += PAGE_SIZE) {
        if (pte_none(*old_pte))
            continue;
        pte = ptep_get_and_clear(mm, old_addr, old_pte);
        pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
        set_pte_at(mm, new_addr, new_pte, pte);
    }

    arch_leave_lazy_mmu_mode();
    if (new_ptl != old_ptl)
        spin_unlock(new_ptl);
    pte_unmap(new_pte - 1);
    pte_unmap_unlock(old_pte - 1, old_ptl);
    if (anon_vma)
        anon_vma_unlock(anon_vma);
    if (mapping)
        mutex_unlock(&mapping->i_mmap_mutex);
}

#define LATENCY_LIMIT   (64 * PAGE_SIZE)

unsigned long move_page_tables(struct vm_area_struct *vma,
        unsigned long old_addr, struct vm_area_struct *new_vma,
        unsigned long new_addr, unsigned long len,
        bool need_rmap_locks)
{
    unsigned long extent, next, old_end;
    pmd_t *old_pmd, *new_pmd;
    bool need_flush = false;
    unsigned long mmun_start;   /* For mmu_notifiers */
    unsigned long mmun_end;     /* For mmu_notifiers */

    old_end = old_addr + len;
    flush_cache_range(vma, old_addr, old_end);

    mmun_start = old_addr;
    mmun_end   = old_end;
    mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);

    for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
        cond_resched();
        next = (old_addr + PMD_SIZE) & PMD_MASK;
        /* even if next overflowed, extent below will be ok */
        extent = next - old_addr;
        if (extent > old_end - old_addr)
            extent = old_end - old_addr;
        old_pmd = get_old_pmd(vma->vm_mm, old_addr);
        if (!old_pmd)
            continue;
        new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
        if (!new_pmd)
            break;
        if (pmd_trans_huge(*old_pmd)) {
            int err = 0;
            if (extent == HPAGE_PMD_SIZE)
                err = move_huge_pmd(vma, new_vma, old_addr,
                            new_addr, old_end,
                            old_pmd, new_pmd);
            if (err > 0) {
                need_flush = true;
                continue;
            } else if (!err) {
                split_huge_page_pmd(vma->vm_mm, old_pmd);
            }
            VM_BUG_ON(pmd_trans_huge(*old_pmd));
        }
        if (pmd_none(*new_pmd) && __pte_alloc(new_vma->vm_mm, new_vma,
                              new_pmd, new_addr))
            break;
        next = (new_addr + PMD_SIZE) & PMD_MASK;
        if (extent > next - new_addr)
            extent = next - new_addr;
        if (extent > LATENCY_LIMIT)
            extent = LATENCY_LIMIT;
        move_ptes(vma, old_pmd, old_addr, old_addr + extent,
              new_vma, new_pmd, new_addr, need_rmap_locks);
        need_flush = true;
    }
    if (likely(need_flush))
        flush_tlb_range(vma, old_end-len, old_addr);

    mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);

    return len + old_addr - old_end;    /* how much done */
}

static unsigned long move_vma(struct vm_area_struct *vma,
        unsigned long old_addr, unsigned long old_len,
        unsigned long new_len, unsigned long new_addr)
{
    struct mm_struct *mm = vma->vm_mm;
    struct vm_area_struct *new_vma;
    unsigned long vm_flags = vma->vm_flags;
    unsigned long new_pgoff;
    unsigned long moved_len;
    unsigned long excess = 0;
    unsigned long hiwater_vm;
    int split = 0;
    int err;
    bool need_rmap_locks;

    /*
     * We'd prefer to avoid failure later on in do_munmap:
     * which may split one vma into three before unmapping.
     */
    if (mm->map_count >= sysctl_max_map_count - 3)
        return -ENOMEM;

    /*
     * Advise KSM to break any KSM pages in the area to be moved:
     * it would be confusing if they were to turn up at the new
     * location, where they happen to coincide with different KSM
     * pages recently unmapped.  But leave vma->vm_flags as it was,
     * so KSM can come around to merge on vma and new_vma afterwards.
     */
    err = ksm_madvise(vma, old_addr, old_addr + old_len,
                        MADV_UNMERGEABLE, &vm_flags);
    if (err)
        return err;

    new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
    new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
               &need_rmap_locks);
    if (!new_vma)
        return -ENOMEM;

    moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
                     need_rmap_locks);
    if (moved_len < old_len) {
        /*
         * On error, move entries back from new area to old,
         * which will succeed since page tables still there,
         * and then proceed to unmap new area instead of old.
         */
        move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
                 true);
        vma = new_vma;
        old_len = new_len;
        old_addr = new_addr;
        new_addr = -ENOMEM;
    }

    /* Conceal VM_ACCOUNT so old reservation is not undone */
    if (vm_flags & VM_ACCOUNT) {
        vma->vm_flags &= ~VM_ACCOUNT;
        excess = vma->vm_end - vma->vm_start - old_len;
        if (old_addr > vma->vm_start &&
            old_addr + old_len < vma->vm_end)
            split = 1;
    }

    /*
     * If we failed to move page tables we still do total_vm increment
     * since do_munmap() will decrement it by old_len == new_len.
     *
     * Since total_vm is about to be raised artificially high for a
     * moment, we need to restore high watermark afterwards: if stats
     * are taken meanwhile, total_vm and hiwater_vm appear too high.
     * If this were a serious issue, we'd add a flag to do_munmap().
     */
    hiwater_vm = mm->hiwater_vm;
    vm_stat_account(mm, vma->vm_flags, vma->vm_file, new_len>>PAGE_SHIFT);

    if (do_munmap(mm, old_addr, old_len) < 0) {
        /* OOM: unable to split vma, just get accounts right */
        vm_unacct_memory(excess >> PAGE_SHIFT);
        excess = 0;
    }
    mm->hiwater_vm = hiwater_vm;

    /* Restore VM_ACCOUNT if one or two pieces of vma left */
    if (excess) {
        vma->vm_flags |= VM_ACCOUNT;
        if (split)
            vma->vm_next->vm_flags |= VM_ACCOUNT;
    }

    if (vm_flags & VM_LOCKED) {
        mm->locked_vm += new_len >> PAGE_SHIFT;
        if (new_len > old_len)
            mlock_vma_pages_range(new_vma, new_addr + old_len,
                               new_addr + new_len);
    }

    return new_addr;
}

static struct vm_area_struct *vma_to_resize(unsigned long addr,
    unsigned long old_len, unsigned long new_len, unsigned long *p)
{
    struct mm_struct *mm = current->mm;
    struct vm_area_struct *vma = find_vma(mm, addr);

    if (!vma || vma->vm_start > addr)
        goto Efault;

    if (is_vm_hugetlb_page(vma))
        goto Einval;

    /* We can't remap across vm area boundaries */
    if (old_len > vma->vm_end - addr)
        goto Efault;

    /* Need to be careful about a growing mapping */
    if (new_len > old_len) {
        unsigned long pgoff;

        if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
            goto Efault;
        pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
        pgoff += vma->vm_pgoff;
        if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
            goto Einval;
    }

    if (vma->vm_flags & VM_LOCKED) {
        unsigned long locked, lock_limit;
        locked = mm->locked_vm << PAGE_SHIFT;
        lock_limit = rlimit(RLIMIT_MEMLOCK);
        locked += new_len - old_len;
        if (locked > lock_limit && !capable(CAP_IPC_LOCK))
            goto Eagain;
    }

    if (!may_expand_vm(mm, (new_len - old_len) >> PAGE_SHIFT))
        goto Enomem;

    if (vma->vm_flags & VM_ACCOUNT) {
        unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
        if (security_vm_enough_memory_mm(mm, charged))
            goto Efault;
        *p = charged;
    }

    return vma;

Efault: /* very odd choice for most of the cases, but... */
    return ERR_PTR(-EFAULT);
Einval:
    return ERR_PTR(-EINVAL);
Enomem:
    return ERR_PTR(-ENOMEM);
Eagain:
    return ERR_PTR(-EAGAIN);
}

static unsigned long mremap_to(unsigned long addr,
    unsigned long old_len, unsigned long new_addr,
    unsigned long new_len)
{
    struct mm_struct *mm = current->mm;
    struct vm_area_struct *vma;
    unsigned long ret = -EINVAL;
    unsigned long charged = 0;
    unsigned long map_flags;

    if (new_addr & ~PAGE_MASK)
        goto out;

    if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
        goto out;

    /* Check if the location we're moving into overlaps the
     * old location at all, and fail if it does.
     */
    if ((new_addr <= addr) && (new_addr+new_len) > addr)
        goto out;

    if ((addr <= new_addr) && (addr+old_len) > new_addr)
        goto out;

    ret = do_munmap(mm, new_addr, new_len);
    if (ret)
        goto out;

    if (old_len >= new_len) {
        ret = do_munmap(mm, addr+new_len, old_len - new_len);
        if (ret && old_len != new_len)
            goto out;
        old_len = new_len;
    }

    vma = vma_to_resize(addr, old_len, new_len, &charged);
    if (IS_ERR(vma)) {
        ret = PTR_ERR(vma);
        goto out;
    }

    map_flags = MAP_FIXED;
    if (vma->vm_flags & VM_MAYSHARE)
        map_flags |= MAP_SHARED;

    ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
                ((addr - vma->vm_start) >> PAGE_SHIFT),
                map_flags);
    if (ret & ~PAGE_MASK)
        goto out1;

    ret = move_vma(vma, addr, old_len, new_len, new_addr);
    if (!(ret & ~PAGE_MASK))
        goto out;
out1:
    vm_unacct_memory(charged);

out:
    return ret;
}

static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
{
    unsigned long end = vma->vm_end + delta;
    if (end < vma->vm_end) /* overflow */
        return 0;
    if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
        return 0;
    if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
                  0, MAP_FIXED) & ~PAGE_MASK)
        return 0;
    return 1;
}

/*
 * Expand (or shrink) an existing mapping, potentially moving it at the
 * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
 *
 * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
 * This option implies MREMAP_MAYMOVE.
 */
SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
        unsigned long, new_len, unsigned long, flags,
        unsigned long, new_addr)
{
    struct mm_struct *mm = current->mm;
    struct vm_area_struct *vma;
    unsigned long ret = -EINVAL;
    unsigned long charged = 0;

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

    if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
        goto out;

    if (addr & ~PAGE_MASK)
        goto out;

    old_len = PAGE_ALIGN(old_len);
    new_len = PAGE_ALIGN(new_len);

    /*
     * We allow a zero old-len as a special case
     * for DOS-emu "duplicate shm area" thing. But
     * a zero new-len is nonsensical.
     */
    if (!new_len)
        goto out;

    if (flags & MREMAP_FIXED) {
        if (flags & MREMAP_MAYMOVE)
            ret = mremap_to(addr, old_len, new_addr, new_len);
        goto out;
    }

    /*
     * Always allow a shrinking remap: that just unmaps
     * the unnecessary pages..
     * do_munmap does all the needed commit accounting
     */
    if (old_len >= new_len) {
        ret = do_munmap(mm, addr+new_len, old_len - new_len);
        if (ret && old_len != new_len)
            goto out;
        ret = addr;
        goto out;
    }

    /*
     * Ok, we need to grow..
     */
    vma = vma_to_resize(addr, old_len, new_len, &charged);
    if (IS_ERR(vma)) {
        ret = PTR_ERR(vma);
        goto out;
    }

    /* old_len exactly to the end of the area..
     */
    if (old_len == vma->vm_end - addr) {
        /* can we just expand the current mapping? */
        if (vma_expandable(vma, new_len - old_len)) {
            int pages = (new_len - old_len) >> PAGE_SHIFT;

            if (vma_adjust(vma, vma->vm_start, addr + new_len,
                       vma->vm_pgoff, NULL)) {
                ret = -ENOMEM;
                goto out;
            }

            vm_stat_account(mm, vma->vm_flags, vma->vm_file, pages);
            if (vma->vm_flags & VM_LOCKED) {
                mm->locked_vm += pages;
                mlock_vma_pages_range(vma, addr + old_len,
                           addr + new_len);
            }
            ret = addr;
            goto out;
        }
    }

    /*
     * We weren't able to just expand or shrink the area,
     * we need to create a new one and move it..
     */
    ret = -ENOMEM;
    if (flags & MREMAP_MAYMOVE) {
        unsigned long map_flags = 0;
        if (vma->vm_flags & VM_MAYSHARE)
            map_flags |= MAP_SHARED;

        new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
                    vma->vm_pgoff +
                    ((addr - vma->vm_start) >> PAGE_SHIFT),
                    map_flags);
        if (new_addr & ~PAGE_MASK) {
            ret = new_addr;
            goto out;
        }

        ret = move_vma(vma, addr, old_len, new_len, new_addr);
    }
out:
    if (ret & ~PAGE_MASK)
        vm_unacct_memory(charged);
    up_write(&current->mm->mmap_sem);
    return ret;
}