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 02:20:56PM +0300, Mark Bloch wrote:
> 
> 
> On 23/04/2025 13:31, Michal Swiatkowski wrote:
> > 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?
> 
> That's why the commit message has: "it only needs to
> be a unicast address. A zeroed-out MAC address is sufficient for this
> purpose."
> 
> I feel this is good enough.

Make sense, thanks

> 
> > 
> > Anyway,
> > Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
> 
> Thanks!
> 
> > 
> > hw_id in mlx5_rdma_make_default_gid() is also used without assigining.
> > Is it fine to have random bits there?
> 
> We pass hw_id to mlx5_query_mac_address() which fills it.
> However, there's a separate issue where mlx5_query_mac_address()
> might fail, this is unlikely, but still possible.
> We'll address that in a follow-up patch.
> 
> Thanks for the review! 
> 
> Mark
> 
> > 
> > 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
>