Re: [PATCH net 2/5] net/mlx5: E-Switch, Initialize MAC Address for Default GID

[Michal Swiatkowski <michal.swiatkowski@linux.intel.com>]

On Wed, Apr 23, 2025 at 11:36:08AM +0300, Mark Bloch wrote:
> From: Maor Gottlieb <maorg@nvidia.com>
> 
> Initialize the source MAC address when creating the default GID entry.
> Since this entry is used only for loopback traffic, it only needs to
> be a unicast address. A zeroed-out MAC address is sufficient for this
> purpose.
> Without this fix, random bits would be assigned as the source address.
> If these bits formed a multicast address, the firmware would return an
> error, preventing the user from switching to switchdev mode:
> 
> Error: mlx5_core: Failed setting eswitch to offloads.
> kernel answers: Invalid argument
> 
> Fixes: 80f09dfc237f ("net/mlx5: Eswitch, enable RoCE loopback traffic")
> Signed-off-by: Maor Gottlieb <maorg@nvidia.com>
> Signed-off-by: Mark Bloch <mbloch@nvidia.com>
> ---
>  drivers/net/ethernet/mellanox/mlx5/core/rdma.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/rdma.c b/drivers/net/ethernet/mellanox/mlx5/core/rdma.c
> index a42f6cd99b74..f585ef5a3424 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/rdma.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/rdma.c
> @@ -118,8 +118,8 @@ static void mlx5_rdma_make_default_gid(struct mlx5_core_dev *dev, union ib_gid *
>  
>  static int mlx5_rdma_add_roce_addr(struct mlx5_core_dev *dev)
>  {
> +	u8 mac[ETH_ALEN] = {};

Won't it be helpful to add comment that it needs to be unicast and 0 is
a valid MAC?

Anyway,
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>

hw_id in mlx5_rdma_make_default_gid() is also used without assigining.
Is it fine to have random bits there?

Thanks

>  	union ib_gid gid;
> -	u8 mac[ETH_ALEN];
>  
>  	mlx5_rdma_make_default_gid(dev, &gid);
>  	return mlx5_core_roce_gid_set(dev, 0,
> -- 
> 2.34.1