Subject: [net 05/12] net/mlx5e: RX, Avoid possible data corruption when relaxed ordering and LRO combined

From: Saeed Mahameed <[email-masked]>
Date: Tue, 27 Jul 2021 16:20:43 -0700

From: Tariq Toukan <[email-masked]>

When HW aggregates packets for an LRO session, it writes the payload
of two consecutive packets of a flow contiguously, so that they usually
share a cacheline.

The first byte of a packet's payload is written immediately after
the last byte of the preceding packet.
In this flow, there are two consecutive write requests to the shared
cacheline:
1. Regular write for the earlier packet.
2. Read-modify-write for the following packet.

In case of relaxed-ordering on, these two writes might be re-ordered.
Using the end padding optimization (to avoid partial write for the last
cacheline of a packet) becomes problematic if the two writes occur
out-of-order, as the padding would overwrite payload that belongs to
the following packet, causing data corruption.

Avoid this by disabling the end padding optimization when both
LRO and relaxed-ordering are enabled.

Fixes: 17347d5430c4 ("net/mlx5e: Add support for PCI relaxed ordering")
Signed-off-by: Tariq Toukan <[email-masked]>
Reviewed-by: Moshe Shemesh <[email-masked]>
Signed-off-by: Saeed Mahameed <[email-masked]>
---
 drivers/net/ethernet/mellanox/mlx5/core/en/params.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/params.c b/drivers/net/ethernet/mellanox/mlx5/core/en/params.c
index 150c8e82c738..2cbf18c967f7 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en/params.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en/params.c
@@ -471,6 +471,15 @@ static void mlx5e_build_rx_cq_param(struct mlx5_core_dev *mdev,
 	param->cq_period_mode = params->rx_cq_moderation.cq_period_mode;
 }
 
+static u8 rq_end_pad_mode(struct mlx5_core_dev *mdev, struct mlx5e_params *params)
+{
+	bool ro = pcie_relaxed_ordering_enabled(mdev->pdev) &&
+		MLX5_CAP_GEN(mdev, relaxed_ordering_write);
+
+	return ro && params->lro_en ?
+		MLX5_WQ_END_PAD_MODE_NONE : MLX5_WQ_END_PAD_MODE_ALIGN;
+}
+
 int mlx5e_build_rq_param(struct mlx5_core_dev *mdev,
 			 struct mlx5e_params *params,
 			 struct mlx5e_xsk_param *xsk,
@@ -508,7 +517,7 @@ int mlx5e_build_rq_param(struct mlx5_core_dev *mdev,
 	}
 
 	MLX5_SET(wq, wq, wq_type,          params->rq_wq_type);
-	MLX5_SET(wq, wq, end_padding_mode, MLX5_WQ_END_PAD_MODE_ALIGN);
+	MLX5_SET(wq, wq, end_padding_mode, rq_end_pad_mode(mdev, params));
 	MLX5_SET(wq, wq, log_wq_stride,
 		 mlx5e_get_rqwq_log_stride(params->rq_wq_type, ndsegs));
 	MLX5_SET(wq, wq, pd,               mdev->mlx5e_res.hw_objs.pdn);
-- 
2.31.1