netdev - Re: [PATCH 1/4] virtio_net: notify MAC address change on device initialization

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Date:   Sun, 22 Jan 2023 15:47:08 +0200
From:   Eli Cohen <elic@...dia.com>
To:     Laurent Vivier <lvivier@...hat.com>, linux-kernel@...r.kernel.org
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Parav Pandit <parav@...dia.com>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        Jason Wang <jasowang@...hat.com>,
        Gautam Dawar <gautam.dawar@...inx.com>,
        Cindy Lu <lulu@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eugenio Pérez <eperezma@...hat.com>
Subject: Re: [PATCH 1/4] virtio_net: notify MAC address change on device
 initialization


On 22/01/2023 12:05, Laurent Vivier wrote:
> 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..25511a86590e 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 (dev->addr_assign_type == NET_ADDR_RANDOM &&
Maybe it's better to not count on addr_assign_type and use a local 
variable to indicate that virtnet_probe assigned random MAC. The reason 
is that the hardware driver might have done that as well and does not 
need notification.
> +	    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: