From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932774Ab3FEVY6 (ORCPT ); Wed, 5 Jun 2013 17:24:58 -0400 Received: from mx1.redhat.com ([209.132.183.28]:9611 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932421Ab3FEVYz (ORCPT ); Wed, 5 Jun 2013 17:24:55 -0400 Date: Wed, 5 Jun 2013 18:24:49 -0300 From: Rafael Aquini To: Luiz Capitulino Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH] virtio_balloon: leak_balloon(): only tell host if we got pages deflated Message-ID: <20130605212449.GB19617@optiplex.redhat.com> References: <20130605171031.7448deea@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130605171031.7448deea@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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! Acked-by: Rafael Aquini > 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 >