On Wed, Dec 14, 2016 at 09:08:52AM -0600, Michael Roth wrote:
> Quoting Maxime Coquelin (2016-12-14 06:52:37)
> > 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-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 <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: Marcel Apfelbaum <mar...@redhat.com>
> > Cc: Dr. David Alan Gilbert <dgilb...@redhat.com>
> > Signed-off-by: Maxime Coquelin <maxime.coque...@redhat.com>
>
> Tested-by: Michael Roth <mdr...@linux.vnet.ibm.com>
>
> I can confirm this fixes the original issue I reported. I also did a
> number of sanity runs with 2.7/2.8/pc-i440fx-2.{6,7,8} using various
> combinations of disable-modern=true/false on hosts with/without virtio-1,
> and some tests with pseries machines as well, and everything seems to
> work.
>
> Thanks for the quick fix!
FYI what I think does not work is a recent kernel on 2.7
machine type and host without virtio 1.
But this is not new.
> > ---
> >
> > 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 &&
> > + !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),
> > DEFINE_PROP_END_OF_LIST(),
> > };
> >
> > diff --git a/hw/virtio/virtio-pci.h b/hw/virtio/virtio-pci.h
> > index b2a996f..1dca223 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 modern_broken;
> > OnOffAuto disable_legacy;
> > uint32_t class_code;
> > uint32_t nvectors;
> > diff --git a/include/hw/compat.h b/include/hw/compat.h
> > index 0f06e11..fe11723 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-modern-broken",\
> > + .value = "on",\
> > },
> >
> > #define HW_COMPAT_2_6 \
> > --
> > 2.9.3
> >
