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From: Maxime Coquelin <maxime.coquelin@redhat.com>
To: dev@dpdk.org, i.maximets@samsung.com, tiwei.bie@intel.com,
	zhihong.wang@intel.com, jasowang@redhat.com, mst@redhat.com
Cc: stable@dpdk.org, Maxime Coquelin <maxime.coquelin@redhat.com>
Subject: [dpdk-dev] [PATCH v2 2/4] vhost: enforce desc flags and content read ordering
Date: Wed, 19 Dec 2018 09:21:11 +0100	[thread overview]
Message-ID: <20181219082113.24455-3-maxime.coquelin@redhat.com> (raw)
In-Reply-To: <20181219082113.24455-1-maxime.coquelin@redhat.com>

A read barrier is required to ensure that the ordering between
descriptor's flags and content reads is enforced.

1. read flags = desc->flags
if (flags & AVAIL_BIT)
2.   read desc->id

There is a control dependency between steps 1 and step 2.
2 could be speculatively executed before 1, which could result
in 'id' to not be updated yet.

Fixes: 2f3225a7d69b ("vhost: add vector filling support for packed ring")
Cc: stable@dpdk.org

Reported-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Acked-by: Ilya Maximets <i.maximets@samsung.com>
---
 lib/librte_vhost/virtio_net.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index 7f37bbbed..a9b1bc55f 100644
--- a/lib/librte_vhost/virtio_net.c
+++ b/lib/librte_vhost/virtio_net.c
@@ -481,6 +481,12 @@ fill_vec_buf_packed(struct virtio_net *dev, struct vhost_virtqueue *vq,
 	if (unlikely(!desc_is_avail(&descs[avail_idx], wrap_counter)))
 		return -1;
 
+	/*
+	 * The ordering between desc flags and desc
+	 * content reads need to be enforced.
+	 */
+	rte_smp_rmb();
+
 	*desc_count = 0;
 	*len = 0;
 
-- 
2.17.2

  parent reply	other threads:[~2018-12-19  8:21 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-19  8:21 [dpdk-dev] [PATCH v2 0/4] vhost: add missing barriers, move prefetching Maxime Coquelin
2018-12-19  8:21 ` [dpdk-dev] [PATCH v2 1/4] vhost: enforce avail index and desc read ordering Maxime Coquelin
2018-12-19 15:47   ` Michael S. Tsirkin
2018-12-19 15:50     ` Maxime Coquelin
2018-12-19  8:21 ` Maxime Coquelin [this message]
2018-12-19  8:21 ` [dpdk-dev] [PATCH v2 3/4] vhost: prefetch descriptor after the read barrier Maxime Coquelin
2018-12-19  8:21 ` [dpdk-dev] [PATCH v2 4/4] vhost: remove useless prefetch for packed ring descriptor Maxime Coquelin
2018-12-19 15:49   ` Michael S. Tsirkin
2018-12-19 15:50 ` [dpdk-dev] [PATCH v2 0/4] vhost: add missing barriers, move prefetching Michael S. Tsirkin
2018-12-19 16:28   ` Ilya Maximets
2018-12-20  4:39 ` Tiwei Bie
2018-12-20 18:19 ` Maxime Coquelin

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