Re: [PATCH net 1/3] net/mlx5e: SHAMPO, Fix header mapping for 64K pages

[Simon Horman <horms@kernel.org>]

On Tue, Oct 28, 2025 at 08:47:17AM +0200, Tariq Toukan wrote:
> From: Dragos Tatulea <dtatulea@nvidia.com>
> 
> HW-GRO is broken on mlx5 for 64K page sizes. The patch in the fixes tag
> didn't take into account larger page sizes when doing an align down
> of max_ksm_entries. For 64K page size, max_ksm_entries is 0 which will skip
> mapping header pages via WQE UMR. This breaks header-data split
> and will result in the following syndrome:
> 
> mlx5_core 0000:00:08.0 eth2: Error cqe on cqn 0x4c9, ci 0x0, qn 0x1133, opcode 0xe, syndrome 0x4, vendor syndrome 0x32
> 00000000: 00 00 00 00 04 4a 00 00 00 00 00 00 20 00 93 32
> 00000010: 55 00 00 00 fb cc 00 00 00 00 00 00 07 18 00 00
> 00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 4a
> 00000030: 00 00 3b c7 93 01 32 04 00 00 00 00 00 00 bf e0
> mlx5_core 0000:00:08.0 eth2: ERR CQE on RQ: 0x1133
> 
> Furthermore, the function that fills in WQE UMRs for the headers
> (mlx5e_build_shampo_hd_umr()) only supports mapping page sizes that
> fit in a single UMR WQE.
> 
> This patch goes back to the old non-aligned max_ksm_entries value and it
> changes mlx5e_build_shampo_hd_umr() to support mapping a large page over
> multiple UMR WQEs.
> 
> This means that mlx5e_build_shampo_hd_umr() can now leave a page only
> partially mapped. The caller, mlx5e_build_shampo_hd_umr(), ensures that

It's not particularly important, but I think the caller is
mlx5e_alloc_rx_hd_mpwqe().

> there are enough UMR WQEs to cover complete pages by working on
> ksm_entries that are multiples of MLX5E_SHAMPO_WQ_HEADER_PER_PAGE.
> 
> Fixes: 8a0ee54027b1 ("net/mlx5e: SHAMPO, Simplify UMR allocation for headers")
> Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
> Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
> ---
>  .../net/ethernet/mellanox/mlx5/core/en_rx.c   | 34 +++++++++----------
>  1 file changed, 16 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
> index 1c79adc51a04..77f7a1ca091d 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
> @@ -679,25 +679,24 @@ static int mlx5e_build_shampo_hd_umr(struct mlx5e_rq *rq,
>  	umr_wqe = mlx5_wq_cyc_get_wqe(&sq->wq, pi);
>  	build_ksm_umr(sq, umr_wqe, shampo->mkey_be, index, ksm_entries);
>  
> -	WARN_ON_ONCE(ksm_entries & (MLX5E_SHAMPO_WQ_HEADER_PER_PAGE - 1));
> -	while (i < ksm_entries) {
> -		struct mlx5e_frag_page *frag_page = mlx5e_shampo_hd_to_frag_page(rq, index);
> +	for ( ; i < ksm_entries; i++, index++) {

Also, if you have to respin for some reason, I would move the
initialisation of i to 0 from it's declaration to the for loop.

...