From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39629) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cHHfW-0004WV-Dx for qemu-devel@nongnu.org; Wed, 14 Dec 2016 17:04:59 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cHHfS-0006ak-DA for qemu-devel@nongnu.org; Wed, 14 Dec 2016 17:04:58 -0500 Received: from mx1.redhat.com ([209.132.183.28]:56244) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cHHfS-0006aP-4D for qemu-devel@nongnu.org; Wed, 14 Dec 2016 17:04:54 -0500 Date: Thu, 15 Dec 2016 00:04:51 +0200 From: "Michael S. Tsirkin" Message-ID: <20161215000438-mutt-send-email-mst@kernel.org> References: <20161214163035.3297-1-maxime.coquelin@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161214163035.3297-1-maxime.coquelin@redhat.com> Subject: Re: [Qemu-devel] [PATCH v3] virtio-pci: Fix cross-version migration with older machines List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Maxime Coquelin Cc: mdroth@linux.vnet.ibm.com, stefanha@redhat.com, qemu-devel@nongnu.org, cornelia.huck@de.ibm.com, marcel@redhat.com, "Dr . David Alan Gilbert" On Wed, Dec 14, 2016 at 05:30:35PM +0100, Maxime Coquelin wrote: > This patch fixes a cross-version migration regression introduced > by commit d1b4259f ("virtio-bus: Plug devices after features are > negotiated"). > > The problem is encountered when host's vhost backend does not support > VIRTIO_F_VERSION_1, and migration is initiated from a v2.7 or prior > machine with virtio-pci modern capabilities enabled to a v2.8 machine. > > In this case, modern capabilities get exposed to the guest by the source, > whereas the target will detect version 1 is not supported so will only > expose legacy capabilities. > > The problem is fixed by introducing a new "x-ignore-backend-features" > property, which is set in v2.7 and prior compatibility modes. Doing this, > v2.7 machine keeps its broken behaviour (enabling modern while version > is not supported), and newer machines will behave correctly. > > Reported-by: Michael Roth > Suggested-by: Stefan Hajnoczi > Cc: Michael S. Tsirkin > Cc: Cornelia Huck > Cc: Dr. David Alan Gilbert > Reviewed-by: Marcel Apfelbaum > Reviewed-by: Stefan Hajnoczi > Tested-by: Michael Roth > Signed-off-by: Maxime Coquelin Reviewed-by: Michael S. Tsirkin > --- > > V3 fixes commit message with the new property name. > V2 changes the naming as proposed by Michael T.and Cornelia, and > fixes commit message. > > hw/virtio/virtio-pci.c | 5 ++++- > hw/virtio/virtio-pci.h | 1 + > include/hw/compat.h | 4 ++++ > 3 files changed, 9 insertions(+), 1 deletion(-) > > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c > index 521ba0b..21c2b9d 100644 > --- a/hw/virtio/virtio-pci.c > +++ b/hw/virtio/virtio-pci.c > @@ -1580,7 +1580,8 @@ static void virtio_pci_device_plugged(DeviceState *d, Error **errp) > * Virtio capabilities present without > * VIRTIO_F_VERSION_1 confuses guests > */ > - if (!virtio_has_feature(vdev->host_features, VIRTIO_F_VERSION_1)) { > + if (!proxy->ignore_backend_features && > + !virtio_has_feature(vdev->host_features, VIRTIO_F_VERSION_1)) { > virtio_pci_disable_modern(proxy); > > if (!legacy) { > @@ -1852,6 +1853,8 @@ static Property virtio_pci_properties[] = { > VIRTIO_PCI_FLAG_DISABLE_PCIE_BIT, false), > DEFINE_PROP_BIT("page-per-vq", VirtIOPCIProxy, flags, > VIRTIO_PCI_FLAG_PAGE_PER_VQ_BIT, false), > + DEFINE_PROP_BOOL("x-ignore-backend-features", VirtIOPCIProxy, > + ignore_backend_features, false), > DEFINE_PROP_END_OF_LIST(), > }; > > diff --git a/hw/virtio/virtio-pci.h b/hw/virtio/virtio-pci.h > index b2a996f..5e07886 100644 > --- a/hw/virtio/virtio-pci.h > +++ b/hw/virtio/virtio-pci.h > @@ -153,6 +153,7 @@ struct VirtIOPCIProxy { > int config_cap; > uint32_t flags; > bool disable_modern; > + bool ignore_backend_features; > OnOffAuto disable_legacy; > uint32_t class_code; > uint32_t nvectors; > diff --git a/include/hw/compat.h b/include/hw/compat.h > index 0f06e11..8dfc7a3 100644 > --- a/include/hw/compat.h > +++ b/include/hw/compat.h > @@ -18,6 +18,10 @@ > .driver = "intel-iommu",\ > .property = "x-buggy-eim",\ > .value = "true",\ > + },{\ > + .driver = "virtio-pci",\ > + .property = "x-ignore-backend-features",\ > + .value = "on",\ > }, > > #define HW_COMPAT_2_6 \ > -- > 2.9.3