netdev - Re: [PATCH 0/4] virtio_net: vdpa: update MAC address when it is generated by virtio-net

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Date:   Mon, 23 Jan 2023 10:25:44 +0100
From:   Laurent Vivier <lvivier@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Parav Pandit <parav@...dia.com>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        Eli Cohen <elic@...dia.com>, 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 0/4] virtio_net: vdpa: update MAC address when it is
 generated by virtio-net

On 1/22/23 11:23, Michael S. Tsirkin wrote:
> On Sun, Jan 22, 2023 at 11:05:22AM +0100, Laurent Vivier wrote:
>> When the MAC address is not provided by the vdpa device virtio_net
>> driver assigns a random one without notifying the device.
>> The consequence, in the case of mlx5_vdpa, is the internal routing
>> tables of the device are not updated and this can block the
>> communication between two namespaces.
>>
>> To fix this problem, use virtnet_send_command(VIRTIO_NET_CTRL_MAC)
>> to set the address from virtnet_probe() when the MAC address is
>> randomly assigned from virtio_net.
>>
>> While I was testing this change I found 3 other bugs in vdpa_sim_net:
>>
>> - vdpa_sim_net sets the VIRTIO_NET_F_MAC even if no MAC address is
>>    provided. So virtio_net doesn't generate a random MAC address and
>>    the MAC address appears to be 00:00:00:00:00:00
>>
>> - vdpa_sim_net never processes the command and virtnet_send_command()
>>    hangs in an infinite loop. To avoid a kernel crash add a timeout
>>    in the loop.
>>
>> - To allow vdpa_sim_net to process the command, replace the cpu_relax()
>>    in the loop by a schedule(). vdpa_sim_net uses a workqueue to process
>>    the queue, and if we don't allow the kernel to schedule, the queue
>>    is not processed and the loop is infinite.
> 
> I'd split these things out as opposed to a series unless there's
> a dependency I missed.

We needed to fix virtio_net before fixing vdpa_sim_net otherwise the 
virtnet_send_command() hangs when we define the vdpa device with "vdpa dev" but without a 
MAC address.

> All this reminds me of
> https://lore.kernel.org/r/20221226074908.8154-5-jasowang%40redhat.com
> 
> how is this patch different/better?
> Pls also CC people involved in that original discussion.

I was not aware of the Jason's series.

It seems to address better the problem, except it triggers the ASSERT_RTNL() in 
virtnet_send_command() when it is called from virtnet_probe().

I will remove patches 2 and 4 from my series.
PATCH 3 can be sent on independently too.

Thanks,
Laurent