[PATCH v2] net/mlx5: fix risk in Rx descriptor read in NEON vector path

[Ruifeng Wang <ruifeng.wang@arm.com>]

In NEON vector PMD, vector load loads two contiguous 8B of
descriptor data into vector register. Given vector load ensures no
16B atomicity, read of the word that includes op_own field could be
reordered after read of other words. In this case, some words could
contain invalid data.

Reloaded qword0 after read barrier to update vector register. This
ensures that the fetched data is correct.

Testpmd single core test on N1SDP/ThunderX2 showed no performance drop.

Fixes: 1742c2d9fab0 ("net/mlx5: fix synchronization on polling Rx completions")
Cc: stable@dpdk.org

Signed-off-by: Ruifeng Wang <ruifeng.wang@arm.com>
Tested-by: Ali Alnubani <alialnu@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>
---
v2: Rebased and added tags that received.

 drivers/net/mlx5/mlx5_rxtx_vec_neon.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/net/mlx5/mlx5_rxtx_vec_neon.h b/drivers/net/mlx5/mlx5_rxtx_vec_neon.h
index 75e8ed7e5a..9079da65de 100644
--- a/drivers/net/mlx5/mlx5_rxtx_vec_neon.h
+++ b/drivers/net/mlx5/mlx5_rxtx_vec_neon.h
@@ -675,6 +675,14 @@ rxq_cq_process_v(struct mlx5_rxq_data *rxq, volatile struct mlx5_cqe *cq,
 		c0 = vld1q_u64((uint64_t *)(p0 + 48));
 		/* Synchronize for loading the rest of blocks. */
 		rte_io_rmb();
+		/* B.0 (CQE 3) reload lower half of the block. */
+		c3 = vld1q_lane_u64((uint64_t *)(p3 + 48), c3, 0);
+		/* B.0 (CQE 2) reload lower half of the block. */
+		c2 = vld1q_lane_u64((uint64_t *)(p2 + 48), c2, 0);
+		/* B.0 (CQE 1) reload lower half of the block. */
+		c1 = vld1q_lane_u64((uint64_t *)(p1 + 48), c1, 0);
+		/* B.0 (CQE 0) reload lower half of the block. */
+		c0 = vld1q_lane_u64((uint64_t *)(p0 + 48), c0, 0);
 		/* Prefetch next 4 CQEs. */
 		if (pkts_n - pos >= 2 * MLX5_VPMD_DESCS_PER_LOOP) {
 			unsigned int next = pos + MLX5_VPMD_DESCS_PER_LOOP;
-- 
2.25.1