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

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 31 Jan 2023 08:43:03 -0500

On Tue, Jan 31, 2023 at 10:01:53AM +0100, Paolo Abeni wrote:
> 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 <[email-masked]>
> > ---
> >  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

We can't really, device has to be ready otherwise
we can't send commands to it.

-- 
MST