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Violators will be prosecuted for from ; Wed, 14 Dec 2016 13:21:09 -0000 Date: Wed, 14 Dec 2016 14:21:01 +0100 From: Cornelia Huck In-Reply-To: <20161214151332-mutt-send-email-mst@kernel.org> References: <20161214125237.20850-1-maxime.coquelin@redhat.com> <20161214141210.22d12962.cornelia.huck@de.ibm.com> <20161214151332-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-Id: <20161214142101.50010eb4.cornelia.huck@de.ibm.com> Subject: Re: [Qemu-devel] [PATCH] virtio-pci: Fix cross-version migration with older machines List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: Maxime Coquelin , mdroth@linux.vnet.ibm.com, stefanha@redhat.com, qemu-devel@nongnu.org, marcel@redhat.com, "Dr . David Alan Gilbert" On Wed, 14 Dec 2016 15:16:13 +0200 "Michael S. Tsirkin" wrote: > On Wed, Dec 14, 2016 at 02:12:10PM +0100, Cornelia Huck wrote: > > On Wed, 14 Dec 2016 13:52:37 +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. > > > > Wait, machine versions or qemu versions? > > > > > > > > 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-modern-broken" 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: Marcel Apfelbaum > > > Cc: Dr. David Alan Gilbert > > > Signed-off-by: Maxime Coquelin > > > --- > > > > > > I'm not sure about the property name, let me know if you have better ideas. > > > I didn't tested migration yet, but I wanted to share the patch while I test it. > > > I tested booting v2.8 and v2.7 machines with !VERSION_1 and get expected result: > > > - v2.8: Virtio-pci probe succeed > > > - v2.7: Virtio-pci probe fails > > > > > > Thanks, > > > Maxime > > > > > > hw/virtio/virtio-pci.c | 4 +++- > > > hw/virtio/virtio-pci.h | 1 + > > > include/hw/compat.h | 4 ++++ > > > 3 files changed, 8 insertions(+), 1 deletion(-) > > > > > > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c > > > index 521ba0b..93f6b54 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->modern_broken && > > > > What you are de facto doing here is ignoring the features supported by > > the backend. Call this ->ignore_backend_features or so? > > > > > + !virtio_has_feature(vdev->host_features, VIRTIO_F_VERSION_1)) { > > > virtio_pci_disable_modern(proxy); > > > > > > if (!legacy) { > > > @@ -1852,6 +1853,7 @@ 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-modern-broken", VirtIOPCIProxy, modern_broken, false), > > > > What about "x-ignore-backend-features"? > > It's just the capability that ignores that backend is legacy. > > x-cap-ignore-backend-legacy > > ? Sounds good. And has the benefit that nobody will be tempted to set that manually :)