From e0bdfe826ec31f787f2ba08f4abed54a342b029b Mon Sep 17 00:00:00 2001
From: Sergio Lopez <slp@redhat.com>
Date: Tue, 10 Mar 2020 05:20:57 -0400
Subject: [PATCH] vm-virtio: queue: add a missing memory barrier in
 get_used_event

Add a missing memory barrier in get_used_event to make sure we see the
last value written by the guest.

Signed-off-by: Sergio Lopez <slp@redhat.com>
---
 vm-virtio/src/queue.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/vm-virtio/src/queue.rs b/vm-virtio/src/queue.rs
index 29a1ac99f..a6436e978 100644
--- a/vm-virtio/src/queue.rs
+++ b/vm-virtio/src/queue.rs
@@ -559,6 +559,8 @@ impl Queue {
                 }
             };
 
+        // This fence ensures we're seeing the latest update from the guest.
+        fence(Ordering::Acquire);
         match mem.read_obj::<u16>(used_event_addr) {
             Ok(ret) => Some(Wrapping(ret)),
             Err(_) => None,