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

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Message-ID: <8bb17aed-d643-2e33-472a-9f237e26e4d1@redhat.com>
Date:   Tue, 31 Jan 2023 10:32:52 +0100
From:   Laurent Vivier <lvivier@...hat.com>
To:     Paolo Abeni <pabeni@...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 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().

Thanks,
Laurent