[dpdk-dev] [PATCH] vhost: flush used->idx update before reading avail->flags

[Huawei Xie <huawei.xie@intel.com>]

update of used->idx and read of avail->flags could be reordered.
memory fence should be used to ensure the order, otherwise guest could see a stale used->idx value after it toggles the interrupt suppression flag.

Signed-off-by: Huawei Xie <huawei.xie@intel.com>
---
 lib/librte_vhost/vhost_rxtx.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/lib/librte_vhost/vhost_rxtx.c b/lib/librte_vhost/vhost_rxtx.c
index 510ffe8..6afba35 100644
--- a/lib/librte_vhost/vhost_rxtx.c
+++ b/lib/librte_vhost/vhost_rxtx.c
@@ -178,6 +178,9 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t queue_id,
 	*(volatile uint16_t *)&vq->used->idx += count;
 	vq->last_used_idx = res_end_idx;
 
+	/* flush used->idx update before we read avail->flags. */
+	rte_mb();
+
 	/* Kick the guest if necessary. */
 	if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT))
 		eventfd_write((int)vq->callfd, 1);
-- 
1.8.1.4