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

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Date:   Tue, 31 Jan 2023 12:41:00 +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 Tue, 2023-01-31 at 10:32 +0100, Laurent Vivier wrote:
> On 1/31/23 10:01, 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 <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?
> 
> It depends if we can send the command using the control command queue or not.
> I don't think we can use a vq before virtio_device_ready().

Sounds reasonable. @Michael: do you have any additional comments?

Thanks!

Paolo