linux-kernel - [PATCH] vdpa/mlx5: Use write memory barrier after updating CQ index

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Date:   Sun, 6 Dec 2020 12:57:19 +0200
From:   Eli Cohen <elic@...dia.com>
To:     <mst@...hat.com>, <jasowang@...hat.com>,
        <virtualization@...ts.linux-foundation.org>,
        <linux-kernel@...r.kernel.org>
CC:     <lulu@...hat.com>, Eli Cohen <elic@...dia.com>
Subject: [PATCH] vdpa/mlx5: Use write memory barrier after updating CQ index

Make sure to put write memory barrier after updating CQ consumer index
so the hardware knows that there are available CQE slots in the queue.

Failure to do this can cause the update of the RX doorbell record to get
updated before the CQ consumer index resulting in CQ overrun.

Change-Id: Ib0ae4c118cce524c9f492b32569179f3c1f04cc1
Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5 devices")
Signed-off-by: Eli Cohen <elic@...dia.com>
---
 drivers/vdpa/mlx5/net/mlx5_vnet.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
index 1f4089c6f9d7..295f46eea2a5 100644
--- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
+++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
@@ -478,6 +478,11 @@ static int mlx5_vdpa_poll_one(struct mlx5_vdpa_cq *vcq)
 static void mlx5_vdpa_handle_completions(struct mlx5_vdpa_virtqueue *mvq, int num)
 {
 	mlx5_cq_set_ci(&mvq->cq.mcq);
+
+	/* make sure CQ cosumer update is visible to the hardware before updating
+	 * RX doorbell record.
+	 */
+	wmb();
 	rx_post(&mvq->vqqp, num);
 	if (mvq->event_cb.callback)
 		mvq->event_cb.callback(mvq->event_cb.private);
-- 
2.27.0