Commit 11380b36 authored by Cornelia Huck's avatar Cornelia Huck Committed by Michael S. Tsirkin
Browse files

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



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have been queried that can handle the VERSION_1 bit being withdrawn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: default avatarCornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent 6d0b908a

hw/s390x/virtio-ccw.c

+12 −0
Original line number Diff line number Diff line
@@ -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;

}

hw/virtio/virtio-bus.c

+3 −0
Original line number Diff line number Diff line
@@ -56,6 +56,9 @@ void virtio_bus_device_plugged(VirtIODevice *vdev, Error **errp) 
    assert(vdc->get_features != NULL);

    vdev->host_features = vdc->get_features(vdev, vdev->host_features,

                                            errp);

    if (klass->post_plugged != NULL) {

        klass->post_plugged(qbus->parent, errp);

    }

}



/* Reset the virtio_bus */

include/hw/virtio/virtio-bus.h

+5 −0
Original line number Diff line number Diff line
@@ -59,6 +59,11 @@ typedef struct VirtioBusClass { 
     * This is called by virtio-bus just after the device is plugged.

     */

    void (*device_plugged)(DeviceState *d, Error **errp);

    /*

     * Re-evaluate setup after feature bits have been validated

     * by the device backend.

     */

    void (*post_plugged)(DeviceState *d, Error **errp);

    /*

     * transport independent exit function.

     * This is called by virtio-bus just before the device is unplugged.