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SubjectRe: [PATCH] virtio_balloon: leak_balloon(): only tell host if we got pages deflated
On Wed, 5 Jun 2013 18:24:49 -0300
Rafael Aquini <aquini@redhat.com> wrote:

> On Wed, Jun 05, 2013 at 05:10:31PM -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.
> >
> > Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
> > ---
> >
> > PS: I didn't get this in practice. I found it by code review. On the other
> > hand, automatic-ballooning was able to put such invalid requests in
> > the virtqueue and QEMU would explode...
> >
>
> Nice catch! The patch looks sane and replicates the check done at
> fill_balloon(). I think we also could use this P.S. as a commentary
> to let others aware of this scenario. Thanks Luiz!

Want me to respin?

> Acked-by: Rafael Aquini <aquini@redhat.com>

Thanks for your review!

>
>
> > PPS: Very lightly tested
> >
> > 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);
> > + if (vb->num_pfns != 0)
> > + tell_host(vb, vb->deflate_vq);
> > mutex_unlock(&vb->balloon_lock);
> > release_pages_by_pfn(vb->pfns, vb->num_pfns);
> > }
> > --
> > 1.8.1.4
> >
>



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