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virtio-pci: Fix cross-version migration with older machines

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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 <mdroth@linux.vnet.ibm.com>
Reviewed-by: Marcel Apfelbaum <marcel@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Message-id: 20161214163035.3297-1-maxime.coquelin@redhat.com
Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Marcel Apfelbaum <marcel@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Maxime Coquelin 2016-12-14 17:30:35 +01:00 • committed by Stefan Hajnoczi
parent d70678a538
commit 66d1c4c19f
3 changed files with 9 additions and 1 deletions
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5
hw/virtio/virtio-pci.c
View file

@ -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->ignore_backend_features &&
!virtio_has_feature(vdev->host_features, VIRTIO_F_VERSION_1)) {
virtio_pci_disable_modern(proxy);
if (!legacy) {
@ -1852,6 +1853,8 @@ 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-ignore-backend-features", VirtIOPCIProxy,
ignore_backend_features, false),
DEFINE_PROP_END_OF_LIST(),
};