As subject says, 802.3ad bonding is not working with virtio network model. The only errors I see is:
No 802.3ad response from the link partner for any adapters in the bond. Dumping the network traffic shows that no LACP packets are sent from the host running with virtio driver, changing to for example e1000 solves this problem with no configuration changes. Is this a known problem? -- Bj(/)rnar