On Wed, Dec 14, 2016 at 4:30 PM, Maxime Coquelin <maxime.coque...@redhat.com> 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 <mdr...@linux.vnet.ibm.com> > Suggested-by: Stefan Hajnoczi <stefa...@redhat.com> > Cc: Michael S. Tsirkin <m...@redhat.com> > Cc: Cornelia Huck <cornelia.h...@de.ibm.com> > Cc: Dr. David Alan Gilbert <dgilb...@redhat.com> > Reviewed-by: Marcel Apfelbaum <mar...@redhat.com> > Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com> > Tested-by: Michael Roth <mdr...@linux.vnet.ibm.com> > Signed-off-by: Maxime Coquelin <maxime.coque...@redhat.com> > --- > > 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",\ > },
Waiting for Michael Tsirkin's R-b before applying. Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com>