From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx105.postini.com [74.125.245.105]) by kanga.kvack.org (Postfix) with SMTP id 6B3B16B0080 for ; Wed, 5 Jun 2013 19:08:46 -0400 (EDT) Date: Wed, 5 Jun 2013 19:08:44 -0400 From: Luiz Capitulino Subject: Re: [PATCH] virtio_balloon: leak_balloon(): only tell host if we got pages deflated Message-ID: <20130605190844.1e96bbde@redhat.com> In-Reply-To: <20130605212449.GB19617@optiplex.redhat.com> References: <20130605171031.7448deea@redhat.com> <20130605212449.GB19617@optiplex.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Rafael Aquini Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org On Wed, 5 Jun 2013 18:24:49 -0300 Rafael Aquini 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 > > --- > > > > 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 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 > > > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org