Quoting Michael S. Tsirkin (2016-12-14 09:15:38)
> 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.
To clarify I was only testing migration compatibility, I assume virtio
on 2.7 machines is still broken for the configuration you mentioned.
The migration tests I ran on the virtio-1 host do cover networking over
a virtio-net device before/after migration with reboots before/after
migration as well though, and the guest in those cases had a 4.8 kernel,
so I think the sanity checks I mentioned also apply for confirming
virtio-net probe is succeeding in the guest.
The non-virtio-1 runs are being done on my local machine and the tests
in that case are a bit more basic and don't involve actively testing
networking. I'll try some manual tests to check this. I guess the main
things to confirm on that front are that after the patch virtio probing:
pc-i440fx-2.6, defaults -> succeeds
pc-i440fx-2.6, disable-modern=true -> succeeds
pc-i440fx-2.6, disable-modern=false -> fails
pc-i440fx-2.7, defaults -> fails
pc-i440fx-2.7, disable-modern=true -> succeeds
pc-i440fx-2.7, disable-modern=false -> fails
pc-i440fx-2.8, defaults -> succeeds
pc-i440fx-2.8, disable-modern=true -> succeeds
pc-i440fx-2.8, disable-modern=false -> succeeds
>
> > > ---
> > >
> > > 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
> > >
>
