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

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Date:   Mon, 23 Jan 2023 10:52:57 +0100
From:   Laurent Vivier <lvivier@...hat.com>
To:     Eli Cohen <elic@...dia.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 1/22/23 14:47, Eli Cohen wrote:
> 
> 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.

eth_hw_addr_random() sets explicitly NET_ADDR_RANDOM, while eth_hw_addr_set() doesn't 
change addr_assign_type so it doesn't seem this value is set by the hardware driver.

So I guess it's the default value (NET_ADDR_PERM) in this case (even if it's a random 
address from the point of view of the hardware).

If you prefer I can replace it by "!virtio_has_feature(vdev, VIRTIO_NET_F_MAC)"?

Thanks,
Laurent