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From:   Liming Sun <limings@nvidia.com>
To:     Andy Shevchenko <andy@infradead.org>,
        Darren Hart <dvhart@infradead.org>,
        Vadim Pasternak <vadimp@mellanox.com>
CC:     Liming Sun <limings@nvidia.com>, <linux-kernel@vger.kernel.org>,
        <platform-driver-x86@vger.kernel.org>
Subject: [PATCH v1 1/1] platform/mellanox: mlxbf-tmfifo: Fix a memory barrier issue
Date:   Fri, 7 May 2021 11:19:14 -0400
Message-ID: <177d12443460bc613aa495fbdbabbbeef43ba7ff.1620400475.git.limings@nvidia.com>
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The virtio framework uses wmb() when updating avail->idx. It
guarantees the write order, but not necessarily loading order
for the code accessing the memory. This commit adds a load barrier
after reading the avail->idx to make sure all the data in the
descriptor is visible. It also adds a barrier when returning the
packet to virtio framework to make sure read/writes are visible to
the virtio code.

Signed-off-by: Liming Sun <limings@nvidia.com>
---
 drivers/platform/mellanox/mlxbf-tmfifo.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/platform/mellanox/mlxbf-tmfifo.c b/drivers/platform/mellanox/mlxbf-tmfifo.c
index bbc4e71..38800e8 100644
--- a/drivers/platform/mellanox/mlxbf-tmfifo.c
+++ b/drivers/platform/mellanox/mlxbf-tmfifo.c
@@ -294,6 +294,9 @@ static irqreturn_t mlxbf_tmfifo_irq_handler(int irq, void *arg)
 	if (vring->next_avail == virtio16_to_cpu(vdev, vr->avail->idx))
 		return NULL;
 
+	/* Make sure 'avail->idx' is visible already. */
+	virtio_rmb(false);
+
 	idx = vring->next_avail % vr->num;
 	head = virtio16_to_cpu(vdev, vr->avail->ring[idx]);
 	if (WARN_ON(head >= vr->num))
@@ -322,7 +325,7 @@ static void mlxbf_tmfifo_release_desc(struct mlxbf_tmfifo_vring *vring,
 	 * done or not. Add a memory barrier here to make sure the update above
 	 * completes before updating the idx.
 	 */
-	mb();
+	virtio_mb(false);
 	vr->used->idx = cpu_to_virtio16(vdev, vr_idx + 1);
 }
 
@@ -733,6 +736,12 @@ static bool mlxbf_tmfifo_rxtx_one_desc(struct mlxbf_tmfifo_vring *vring,
 		desc = NULL;
 		fifo->vring[is_rx] = NULL;
 
+		/*
+		 * Make sure the load/store are in order before
+		 * returning back to virtio.
+		 */
+		virtio_mb(false);
+
 		/* Notify upper layer that packet is done. */
 		spin_lock_irqsave(&fifo->spin_lock[is_rx], flags);
 		vring_interrupt(0, vring->vq);
-- 
1.8.3.1