netdev - Re: [PATCH v3 2/2] virtio_net: notify MAC address change on device initialization

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Message-ID: <949500bd10077989eb21bd41d6bb1a0de296f9d8.camel@redhat.com>
Date:   Tue, 31 Jan 2023 10:01:53 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Laurent Vivier <lvivier@...hat.com>, linux-kernel@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        virtualization@...ts.linux-foundation.org,
        Cindy Lu <lulu@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>, Eli Cohen <elic@...dia.com>,
        Gautam Dawar <gautam.dawar@...inx.com>,
        Eugenio Pérez <eperezma@...hat.com>,
        Jason Wang <jasowang@...hat.com>, netdev@...r.kernel.org,
        Parav Pandit <parav@...dia.com>
Subject: Re: [PATCH v3 2/2] virtio_net: notify MAC address change on device
 initialization

On Fri, 2023-01-27 at 21:45 +0100, 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:
> RX packets are dropped since they don't go through the receive filters,
> TX packets go through unaffected.
> 
> Signed-off-by: Laurent Vivier <lvivier@...hat.com>
> ---
>  drivers/net/virtio_net.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 7d700f8e545a..704a05f1c279 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -3806,6 +3806,8 @@ 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 */
> @@ -3933,6 +3935,24 @@ static int virtnet_probe(struct virtio_device *vdev)
>  
>  	virtio_device_ready(vdev);
>  
> +	/* a random MAC address has been assigned, notify the device.
> +	 * We don't fail probe if VIRTIO_NET_F_CTRL_MAC_ADDR is not there
> +	 * because many devices work fine without getting MAC explicitly
> +	 */
> +	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)) {
> +			pr_debug("virtio_net: setting MAC address failed\n");
> +			rtnl_unlock();
> +			err = -EINVAL;
> +			goto free_unregister_netdev;

Since the above is still dealing with device initialization, would it
make sense moving such init step before registering the netdevice? 

Cheers,

Paolo