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由 Michael S. Tsirkin 提交于
virtio has the equivalent of: if (vq->last_avail_index != vring_avail_idx(vq)) { read descriptor head at vq->last_avail_index; } In theory, processor can reorder descriptor head read to happen speculatively before the index read. this would trigger the following race: host descriptor head read <- reads invalid head from ring guest writes valid descriptor head guest writes avail index host avail index read <- observes valid index as a result host will use an invalid head value. This was not observed in the field by me but after the experience with the previous two races I think it is prudent to address this theoretical race condition. Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
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