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SubjectRe: [PATCH v2] virtio_balloon: leak_balloon(): only tell host if we got pages deflated
On Wed, Jun 05, 2013 at 09:18:37PM -0400, Luiz Capitulino wrote:
> The balloon_page_dequeue() function can return NULL. If it does for
> the first page being freed, then leak_balloon() will create a
> scatter list with len=0. Which in turn seems to generate an invalid
> virtio request.
>
> I didn't get this in practice, I found it by code review. On the other
> hand, such an invalid virtio request will cause errors in QEMU and
> fill_balloon() also performs the same check implemented by this commit.
>
> Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
> Acked-by: Rafael Aquini <aquini@redhat.com>
> ---
>
> o v2
>
> - Improve changelog
>
> drivers/virtio/virtio_balloon.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index bd3ae32..71af7b5 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -191,7 +191,8 @@ static void leak_balloon(struct virtio_balloon *vb, size_t num)
> * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST);
> * is true, we *have* to do it in this order
> */
> - tell_host(vb, vb->deflate_vq);

Luiz, sorry for not being clearer before. I was referring to add a commentary on
code, to explain in short words why we should not get rid of this check point.

> + if (vb->num_pfns != 0)
> + tell_host(vb, vb->deflate_vq);
> mutex_unlock(&vb->balloon_lock);

If the comment is regarded as unnecessary, then just ignore my suggestion. I'm
OK with your patch. :)

Cheers!
-- Rafael



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