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

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Date:   Sun, 22 Jan 2023 05:23:44 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Laurent Vivier <lvivier@...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 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.

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.

Thanks!

> Laurent Vivier (4):
>   virtio_net: notify MAC address change on device initialization
>   virtio_net: add a timeout in virtnet_send_command()
>   vdpa_sim_net: don't always set VIRTIO_NET_F_MAC
>   virtio_net: fix virtnet_send_command() with vdpa_sim_net
> 
>  drivers/net/virtio_net.c             | 21 +++++++++++++++++++--
>  drivers/vdpa/vdpa_sim/vdpa_sim_net.c |  6 ++++++
>  2 files changed, 25 insertions(+), 2 deletions(-)
> 
> -- 
> 2.39.0
>