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