Re: [PATCH net 4/5] net/mlx5e: Fix wraparound in rate limiting for values above 255 Gbps

[Gal Pressman <gal@nvidia.com>]

On 20/11/2025 23:42, Danielle Costantino wrote:
> On Sun, Nov 9, 2025 at 11:37:52AM +0200, Gal Pressman wrote:
>> Add validation to reject rates exceeding 255 Gbps that would overflow
>> the 8 bits max bandwidth field.
> 
> Hi Gal, Tariq, Paolo,
> 
> While reviewing this commit (43b27d1bd88a) for backporting, I believe
> I've found a logic error in the validation condition.
> 
> The issue is on line 617:
> 
>     } else if (max_bw_value[i] <= upper_limit_gbps) {
>         max_bw_value[i] = div_u64(maxrate->tc_maxrate[i], MLX5E_1GB);
>         max_bw_unit[i]  = MLX5_GBPS_UNIT;
> 
> Suggested fix:
> --------------
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_dcbnl.c b/drivers/net/ethernet/mellanox/mlx5/core/en_dcbnl.c
> index d88a48210fdc..XXXXXXXX 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_dcbnl.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_dcbnl.c
> @@ -614,7 +614,7 @@ static int mlx5e_dcbnl_ieee_setmaxrate(struct net_device *netdev,
>  						  MLX5E_100MB);
>  			max_bw_value[i] = max_bw_value[i] ? max_bw_value[i] : 1;
>  			max_bw_unit[i]  = MLX5_100_MBPS_UNIT;
> -		} else if (max_bw_value[i] <= upper_limit_gbps) {
> +		} else if (maxrate->tc_maxrate[i] <= upper_limit_gbps) {
>  			max_bw_value[i] = div_u64(maxrate->tc_maxrate[i],
>  						  MLX5E_1GB);
>  			max_bw_unit[i]  = MLX5_GBPS_UNIT;
> 
> Let me know if you'd like me to send a formal patch for this.

Hi Danielle,
Your fix is correct, please submit a patch.

Thanks for catching this!