netdev - [PATCH v2 1/1] virtio_net: notify MAC address change on device initialization

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Date:   Mon, 23 Jan 2023 13:00:22 +0100
From:   Laurent Vivier <lvivier@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Gautam Dawar <gautam.dawar@...inx.com>,
        Eugenio Pérez <eperezma@...hat.com>,
        netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        Eli Cohen <elic@...dia.com>, Cindy Lu <lulu@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Parav Pandit <parav@...dia.com>
Subject: [PATCH v2 1/1] virtio_net: notify MAC address change on device initialization

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@...hat.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