Virtualization - Jan 2023 - [PATCH v2 0/1] virtio_net: vdpa: update MAC address when it is generated by virtio-net

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
not provided by the device.

v2:
  - remove vdpa_sim related fixes
  - check virtio_has_feature(vdev, VIRTIO_NET_F_MAC) rather than
    addr_assign_type

Laurent Vivier (1):
  virtio_net: notify MAC address change on device initialization

 drivers/net/virtio_net.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

-- 
2.39.0

In virtnet_probe(), if the device doesn't provide a MAC address the
driver assigns a random one.
As we modify the MAC address we need to notify the device to allow it
to update all the related information.

The problem can be seen with vDPA and mlx5_vdpa driver as it doesn't
assign a MAC address by default. The virtio_net device uses a random
MAC address (we can see it with "ip link"), but we can't ping a
net
namespace from another one using the virtio-vdpa device because the
new MAC address has not been provided to the hardware.

Signed-off-by: Laurent Vivier <lvivier at redhat.com>
---
 drivers/net/virtio_net.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 7723b2a49d8e..4bdc8286678b 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -3800,6 +3800,8 @@ static int virtnet_probe(struct virtio_device *vdev)
 		eth_hw_addr_set(dev, addr);
 	} else {
 		eth_hw_addr_random(dev);
+		dev_info(&vdev->dev, "Assigned random MAC address %pM\n",
+			 dev->dev_addr);
 	}
 
 	/* Set up our device-specific information */
@@ -3956,6 +3958,18 @@ static int virtnet_probe(struct virtio_device *vdev)
 	pr_debug("virtnet: registered device %s with %d RX and TX
vq's\n",
 		 dev->name, max_queue_pairs);
 
+	/* a random MAC address has been assigned, notify the device */
+	if (!virtio_has_feature(vdev, VIRTIO_NET_F_MAC) &&
+	    virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_MAC_ADDR)) {
+		struct scatterlist sg;
+
+		sg_init_one(&sg, dev->dev_addr, dev->addr_len);
+		if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_MAC,
+					  VIRTIO_NET_CTRL_MAC_ADDR_SET, &sg)) {
+			dev_warn(&vdev->dev, "Failed to update MAC address.\n");
+		}
+	}
+
 	return 0;
 
 free_unregister_netdev:
-- 
2.39.0