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: sta...@dpdk.org
Reported-by: Jason Wang <jasow...@redhat.com>
Signed-off-by: Maxime Coquelin <maxime.coque...@redhat.com>
Acked-by: Ilya Maximets <i.maxim...@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
