When the MAC address is not provided by the vdpa device virtio_net
driver assigns a random one without notifying the device.
The consequence, in the case of mlx5_vdpa, is the internal routing
tables of the device are not updated and this can block the
communication between two namespaces.

To fix this problem, use virtnet_send_command(VIRTIO_NET_CTRL_MAC)
to set the address from virtnet_probe() when the MAC address is
randomly assigned from virtio_net.

While I was testing this change I found 3 other bugs in vdpa_sim_net:

- vdpa_sim_net sets the VIRTIO_NET_F_MAC even if no MAC address is
  provided. So virtio_net doesn't generate a random MAC address and
  the MAC address appears to be 00:00:00:00:00:00

- vdpa_sim_net never processes the command and virtnet_send_command()
  hangs in an infinite loop. To avoid a kernel crash add a timeout
  in the loop.

- To allow vdpa_sim_net to process the command, replace the cpu_relax()
  in the loop by a schedule(). vdpa_sim_net uses a workqueue to process
  the queue, and if we don't allow the kernel to schedule, the queue
  is not processed and the loop is infinite.

Laurent Vivier (4):
  virtio_net: notify MAC address change on device initialization
  virtio_net: add a timeout in virtnet_send_command()
  vdpa_sim_net: don't always set VIRTIO_NET_F_MAC
  virtio_net: fix virtnet_send_command() with vdpa_sim_net

 drivers/net/virtio_net.c             | 21 +++++++++++++++++++--
 drivers/vdpa/vdpa_sim/vdpa_sim_net.c |  6 ++++++
 2 files changed, 25 insertions(+), 2 deletions(-)

-- 
2.39.0