virtio_net: disable VIRTIO_NET_F_STANDBY if VIRTIO_NET_F_MAC is not set

Bugzilla: http://bugzilla.redhat.com/2153210

commit 7c06458
Author: Laurent Vivier <lvivier@redhat.com>
Date:   Fri Jan 27 21:44:59 2023 +0100

    virtio_net: disable VIRTIO_NET_F_STANDBY if VIRTIO_NET_F_MAC is not set

    failover relies on the MAC address to pair the primary and the standby
    devices:

      "[...] the hypervisor needs to enable VIRTIO_NET_F_STANDBY
       feature on the virtio-net interface and assign the same MAC address
       to both virtio-net and VF interfaces."

      Documentation/networking/net_failover.rst

    This patch disables the STANDBY feature if the MAC address is not
    provided by the hypervisor.

    Signed-off-by: Laurent Vivier <lvivier@redhat.com>
    Acked-by: Michael S. Tsirkin <mst@redhat.com>
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Laurent Vivier <lvivier@redhat.com>

Author: vivier

drivers/net/virtio_net.c

@@ -3100,6 +3100,12 @@ static int virtnet_validate(struct virtio_device *vdev)
 			__virtio_clear_bit(vdev, VIRTIO_NET_F_MTU);
 	}
 
+	if (virtio_has_feature(vdev, VIRTIO_NET_F_STANDBY) &&
+	    !virtio_has_feature(vdev, VIRTIO_NET_F_MAC)) {
+		dev_warn(&vdev->dev, "device advertises feature VIRTIO_NET_F_STANDBY but not VIRTIO_NET_F_MAC, disabling standby");
+		__virtio_clear_bit(vdev, VIRTIO_NET_F_STANDBY);
+	}
+
 	return 0;
 }