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    SubjectRe: [Xen-devel] [PATCH v4 8/9] xen/gntdev.c: Convert to use vm_map_pages()
    On Fri, Feb 15, 2019 at 08:18:31AM +0530, Souptick Joarder wrote:
    > Convert to use vm_map_pages() to map range of kernel
    > memory to user vma.
    >
    > map->count is passed to vm_map_pages() and internal API
    > verify map->count against count ( count = vma_pages(vma))
    > for page array boundary overrun condition.

    This commit breaks gntdev driver. If vma->vm_pgoff > 0, vm_map_pages
    will:
    - use map->pages starting at vma->vm_pgoff instead of 0
    - verify map->count against vma_pages()+vma->vm_pgoff instead of just
    vma_pages().

    In practice, this breaks using a single gntdev FD for mapping multiple
    grants.

    It looks like vm_map_pages() is not a good fit for this code and IMO it
    should be reverted.

    > Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
    > Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
    > ---
    > drivers/xen/gntdev.c | 11 ++++-------
    > 1 file changed, 4 insertions(+), 7 deletions(-)
    >
    > diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
    > index 5efc5ee..5d64262 100644
    > --- a/drivers/xen/gntdev.c
    > +++ b/drivers/xen/gntdev.c
    > @@ -1084,7 +1084,7 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
    > int index = vma->vm_pgoff;
    > int count = vma_pages(vma);
    > struct gntdev_grant_map *map;
    > - int i, err = -EINVAL;
    > + int err = -EINVAL;
    >
    > if ((vma->vm_flags & VM_WRITE) && !(vma->vm_flags & VM_SHARED))
    > return -EINVAL;
    > @@ -1145,12 +1145,9 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
    > goto out_put_map;
    >
    > if (!use_ptemod) {
    > - for (i = 0; i < count; i++) {
    > - err = vm_insert_page(vma, vma->vm_start + i*PAGE_SIZE,
    > - map->pages[i]);
    > - if (err)
    > - goto out_put_map;
    > - }
    > + err = vm_map_pages(vma, map->pages, map->count);
    > + if (err)
    > + goto out_put_map;
    > } else {
    > #ifdef CONFIG_X86
    > /*

    --
    Best Regards,
    Marek Marczykowski-Górecki
    Invisible Things Lab
    A: Because it messes up the order in which people normally read text.
    Q: Why is top-posting such a bad thing?
    [unhandled content-type:application/pgp-signature]
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