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virtio: handle non-virtio-1-capable backend for ccw

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If you run a qemu advertising VERSION_1 with an old kernel where
vhost did not yet support VERSION_1, you'll end up with a device
that is {modern pci|ccw revision 1} but does not advertise VERSION_1.
This is not a sensible configuration and is rejected by the Linux
guest drivers.

To fix this, add a ->post_plugged() callback invoked after features
have been queried that can handle the VERSION_1 bit being withdrawn
and change ccw to fall back to revision 0 if VERSION_1 is gone.

Note that pci is _not_ fixed; we'll need to rethink the approach
for the next release but at least for pci it's not a regression.

Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Cornelia Huck 2015-12-02 18:31:57 +01:00 • committed by Michael S. Tsirkin
parent 6d0b908a62
commit 11380b3619
3 changed files with 20 additions and 0 deletions
Download patch file Download diff file Expand all files Collapse all files

12
hw/s390x/virtio-ccw.c
View file

@ -1555,6 +1555,17 @@ static void virtio_ccw_device_plugged(DeviceState *d, Error **errp)
d->hotplugged, 1);
}
static void virtio_ccw_post_plugged(DeviceState *d, Error **errp)
{
VirtioCcwDevice *dev = VIRTIO_CCW_DEVICE(d);
VirtIODevice *vdev = virtio_bus_get_device(&dev->bus);
if (!virtio_host_has_feature(vdev, VIRTIO_F_VERSION_1)) {
/* A backend didn't support modern virtio. */
dev->max_rev = 0;
}
}
static void virtio_ccw_device_unplugged(DeviceState *d)
{
VirtioCcwDevice *dev = VIRTIO_CCW_DEVICE(d);
@ -1891,6 +1902,7 @@ static void virtio_ccw_bus_class_init(ObjectClass *klass, void *data)
k->save_config = virtio_ccw_save_config;
k->load_config = virtio_ccw_load_config;
k->device_plugged = virtio_ccw_device_plugged;
k->post_plugged = virtio_ccw_post_plugged;
k->device_unplugged = virtio_ccw_device_unplugged;
}