On Wed, 14 Dec 2016 15:16:13 +0200 "Michael S. Tsirkin" <[email protected]> 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 <[email protected]> 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 <[email protected]> > > > Suggested-by: Stefan Hajnoczi <[email protected]> > > > Cc: Michael S. Tsirkin <[email protected]> > > > Cc: Cornelia Huck <[email protected]> > > > Cc: Marcel Apfelbaum <[email protected]> > > > Cc: Dr. David Alan Gilbert <[email protected]> > > > Signed-off-by: Maxime Coquelin <[email protected]> > > > --- > > > > > > 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 :)
