Re: [Qemu-devel] [PATCH v3] virtio-pci: Fix cross-version migration with older machines

[Cornelia Huck]

On Thu, 15 Dec 2016 07:38:09 +0000
Stefan Hajnoczi <address@hidden> wrote:

> On Wed, Dec 14, 2016 at 05:30:35PM +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.
> > 
> > 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 <address@hidden>
> > Suggested-by: Stefan Hajnoczi <address@hidden>
> > Cc: Michael S. Tsirkin <address@hidden>
> > Cc: Cornelia Huck <address@hidden>
> > Cc: Dr. David Alan Gilbert <address@hidden>
> > Reviewed-by: Marcel Apfelbaum <address@hidden>
> > Reviewed-by: Stefan Hajnoczi <address@hidden>
> > Tested-by: Michael Roth <address@hidden>
> > Signed-off-by: Maxime Coquelin <address@hidden>
> > ---
> > 
> > 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(-)
> 
> Thanks, applied to my staging tree:
> https://github.com/stefanha/qemu/commits/staging
> 
> Stefan

Hm, missing my R-b I gave for v2... feel free to add

Reviewed-by: Cornelia Huck <address@hidden>

if you still want to change it.