net/mlx5e: Add padding when needed in UMR WQEs

Per the device spec, MTTs/KLMs list in a UMR WQE must be aligned to 64B.
Per our SW design, the MTT/KLMs list would need alignment only if it's
too small, for example on PPC when PAGE_SIZE is 64KB, and only 4 pages
are needed to cover a MPWQE of size 256KB.

Padding, if needed, is taken into account when calculating the UMR WQE
fields (ds_cnt and xlt_octowords), however no entries are provided,
instead garbage is passed.

No real harm though, as these parts act as gaps between the RX MPWQEs
and not used by any of them. Hence, in practice, device does not try to
write any incoming packet to them. Still, prefer providing clean padding
marking the end of the list, and do not map garbage into the RQ memory
region.
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Gal Pressman <gal@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>

drivers/net/ethernet/mellanox/mlx5/core/en_rx.c

@@ -727,6 +727,17 @@ static int mlx5e_alloc_rx_mpwqe(struct mlx5e_rq *rq, u16 ix)
 		};
 	}
 
+	/* Pad if needed, in case the value set to ucseg->xlt_octowords
+	 * in mlx5e_build_umr_wqe() needed alignment.
+	 */
+	if (rq->mpwqe.pages_per_wqe & (MLX5_UMR_MTT_NUM_ENTRIES_ALIGNMENT - 1)) {
+		int pad = ALIGN(rq->mpwqe.pages_per_wqe, MLX5_UMR_MTT_NUM_ENTRIES_ALIGNMENT) -
+			rq->mpwqe.pages_per_wqe;
+
+		memset(&umr_wqe->inline_mtts[rq->mpwqe.pages_per_wqe], 0,
+		       sizeof(*umr_wqe->inline_mtts) * pad);
+	}
+
 	bitmap_zero(wi->xdp_xmit_bitmap, rq->mpwqe.pages_per_wqe);
 	wi->consumed_strides = 0;
 

include/linux/mlx5/device.h

@@ -294,6 +294,7 @@ enum {
 #define MLX5_UMR_MTT_ALIGNMENT 0x40
 #define MLX5_UMR_MTT_MASK      (MLX5_UMR_MTT_ALIGNMENT - 1)
 #define MLX5_UMR_MTT_MIN_CHUNK_SIZE MLX5_UMR_MTT_ALIGNMENT
+#define MLX5_UMR_MTT_NUM_ENTRIES_ALIGNMENT (MLX5_UMR_MTT_ALIGNMENT / sizeof(struct mlx5_mtt))
 
 #define MLX5_USER_INDEX_LEN (MLX5_FLD_SZ_BYTES(qpc, user_index) * 8)