linux-kernel - Re: [PATCH] vdpa/mlx5: Use random MAC for the vdpa net instance

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Date:   Sun, 29 Nov 2020 15:08:22 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Eli Cohen <elic@...dia.com>
Cc:     jasowang@...hat.com, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, lulu@...hat.com
Subject: Re: [PATCH] vdpa/mlx5: Use random MAC for the vdpa net instance

On Sun, Nov 29, 2020 at 08:43:51AM +0200, Eli Cohen wrote:
> We should not try to use the VF MAC address as that is used by the
> regular (e.g. mlx5_core) NIC implementation. Instead, use a random
> generated MAC address.
> 
> Suggested by: Cindy Lu <lulu@...hat.com>
> Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5 devices")
> Signed-off-by: Eli Cohen <elic@...dia.com>

I didn't realise it's possible to use VF in two ways
with and without vdpa.
Could you include a bit more description on the failure
mode?
Is switching to a random mac for such an unusual
configuration really justified?
It looks like changing a MAC could break some guests,
can it not?

> ---
>  drivers/vdpa/mlx5/net/mlx5_vnet.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> index 1fa6fcac8299..80d06d958b8b 100644
> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> @@ -1955,10 +1955,7 @@ void *mlx5_vdpa_add_dev(struct mlx5_core_dev *mdev)
>  	if (err)
>  		goto err_mtu;
>  
> -	err = mlx5_query_nic_vport_mac_address(mdev, 0, 0, config->mac);
> -	if (err)
> -		goto err_mtu;
> -
> +	eth_random_addr(config->mac);
>  	mvdev->vdev.dma_dev = mdev->device;
>  	err = mlx5_vdpa_alloc_resources(&ndev->mvdev);
>  	if (err)
> -- 
> 2.26.2