static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
    unsigned long start, unsigned long end, unsigned int newflags)
{
    struct mm_struct * mm = vma->vm_mm;
    int pages;
    int ret;

#ifdef CONFIG_PAX_SEGMEXEC
    struct vm_area_struct * vma_m = NULL, *prev_m;
    unsigned long start_m = 0UL, end_m = 0UL, newflags_m = 0UL;

    if (vma->vm_flags & VM_MIRROR) {
        start_m = vma->vm_start + vma->vm_mirror;
        vma_m = find_vma_prev(mm, start_m, &prev_m);
        if (!vma_m || vma_m->vm_start != start_m || !(vma_m->vm_flags & VM_MIRROR)) {
            printk("PAX: VMMIRROR: mlock bug in %s, %08lx\n", current->comm, vma->vm_start);
            return -ENOMEM;
        }

        start_m = start + vma->vm_mirror;
        end_m = end + vma->vm_mirror;
        if (newflags & VM_LOCKED)
            newflags_m = vma_m->vm_flags | VM_LOCKED;
        else
            newflags_m = vma_m->vm_flags & ~VM_LOCKED;
        ret = __mlock_fixup(vma_m, &prev_m, start_m, end_m, newflags_m);
        if (ret)
            return ret;
    }
#endif

    ret = __mlock_fixup(vma, prev, start, end, newflags);
    if (ret)
        return ret;

    /*
     * 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, make_pages_present below will bring it back.
     */
    vma->vm_flags = newflags;

#ifdef CONFIG_PAX_SEGMEXEC
    if (vma->vm_flags & VM_MIRROR)
        vma_m->vm_flags = newflags_m;
#endif

    /*
     * Keep track of amount of locked VM.
     */
    pages = (end - start) >> PAGE_SHIFT;
    if (newflags & VM_LOCKED) {
        pages = -pages;
        if (!(newflags & VM_IO))
            ret = make_pages_present(start, end);
    }

    mm->locked_vm -= pages;

#ifdef CONFIG_PAX_SEGMEXEC
    if (vma->vm_flags & VM_MIRROR)
        mm->locked_vm -= pages;
#endif
    if (ret == -ENOMEM)
        ret = -EAGAIN;
    return ret;
}

static int __mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
    unsigned long start, unsigned long end, unsigned int newflags)
{
    struct mm_struct * mm = vma->vm_mm;
    pgoff_t pgoff;
    int ret = 0;

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

    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 out;
    }

    *prev = vma;

    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);

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