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vm-virtio: Fix update_avail_event() memory ordering

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We should use full memory barrier to ensure both guest and us
can see the correct avail_idx and avail_event_idx. Something
like this pattern:

VM:                           CLH:
update vring.avail->idx       update avail_event_idx
mb()                          mb()
read avail_event_idx          read vring.avail->idx

Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
This commit is contained in:
Xie Yongji 2021-01-19 17:17:53 +08:00 committed by Sebastien Boeuf
parent 79a2afe44e
commit 72b736153e
1 changed files with 2 additions and 2 deletions
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4
vm-virtio/src/queue.rs
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@ -607,8 +607,8 @@ impl Queue {
None => warn!("Can't update avail_event"),
}
// This fence ensures the guest sees the value we've just written.
fence(Ordering::Release);
// This fence ensures both guest and us see the correct value (avail idx and avail event)
fence(Ordering::SeqCst);
}
/// Return the value present in the used_event field of the avail ring.