From d4ff2135ebb6c7f55af783846fa8e7ea4379c71b Mon Sep 17 00:00:00 2001 From: Maxime Coquelin Date: Wed, 19 Dec 2018 09:21:10 +0100 Subject: [PATCH] vhost: enforce avail index and desc read ordering 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 Signed-off-by: Maxime Coquelin Acked-by: Ilya Maximets Acked-by: Michael S. Tsirkin Acked-by: Tiwei Bie --- 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 8c657a1013..7f37bbbed6 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); -- 2.20.1