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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 1/4] vhost: enforce avail index and desc read ordering
Date: Wed, 19 Dec 2018 09:21:10 +0100	[thread overview]
Message-ID: <20181219082113.24455-2-maxime.coquelin@redhat.com> (raw)
In-Reply-To: <20181219082113.24455-1-maxime.coquelin@redhat.com>

A read barrier is required to ensure the ordering between
available index and the descriptor reads is enforced.

1. read avail_head = avail->idx
2. read cur_idx = last_avail_idx
if (cur_idx != avail_head) {
    3. read idx = avail->ring[cur_idx]
    4. read desc[idx]
}

There is a control dependency between step 1 and steps 3 & 4,
3 could be speculatively executed before 1, which could result
in 'idx' to not being updated yet.

Fixes: 4796ad63ba1f ("examples/vhost: import userspace vhost application")
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 | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index 8c657a101..7f37bbbed 100644
--- a/lib/librte_vhost/virtio_net.c
+++ b/lib/librte_vhost/virtio_net.c
@@ -752,6 +752,12 @@ virtio_dev_rx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
 	rte_prefetch0(&vq->avail->ring[vq->last_avail_idx & (vq->size - 1)]);
 	avail_head = *((volatile uint16_t *)&vq->avail->idx);
 
+	/*
+	 * The ordering between avail index and
+	 * desc reads needs to be enforced.
+	 */
+	rte_smp_rmb();
+
 	for (pkt_idx = 0; pkt_idx < count; pkt_idx++) {
 		uint32_t pkt_len = pkts[pkt_idx]->pkt_len + dev->vhost_hlen;
 		uint16_t nr_vec = 0;
@@ -1334,6 +1340,12 @@ virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
 	if (free_entries == 0)
 		return 0;
 
+	/*
+	 * The ordering between avail index and
+	 * desc reads needs to be enforced.
+	 */
+	rte_smp_rmb();
+
 	VHOST_LOG_DEBUG(VHOST_DATA, "(%d) %s\n", dev->vid, __func__);
 
 	count = RTE_MIN(count, MAX_PKT_BURST);
-- 
2.17.2

  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 ` Maxime Coquelin [this message]
2018-12-19 15:47   ` [dpdk-dev] [PATCH v2 1/4] vhost: enforce avail index and desc read ordering Michael S. Tsirkin
2018-12-19 15:50     ` Maxime Coquelin
2018-12-19  8:21 ` [dpdk-dev] [PATCH v2 2/4] vhost: enforce desc flags and content " Maxime Coquelin
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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