On 2018年05月16日 20:32, Jason Wang wrote:
+static bool vhost_notify_packed(struct vhost_dev *dev,
+ struct vhost_virtqueue *vq)
+{
+ __virtio16 event_off_wrap, event_flags;
+ __u16 old, new, off_wrap;
+ bool v;
+
+ /* Flush out used descriptors updates. This is paired
+ * with the barrier that the Guest executes when enabling
+ * interrupts.
+ */
+ smp_mb();
+
+ if (vhost_get_avail(vq, event_flags,
+ &vq->driver_event->flags) < 0) {
+ vq_err(vq, "Failed to get driver desc_event_flags");
+ return true;
+ }
+
+ if (event_flags == cpu_to_vhost16(vq, RING_EVENT_FLAGS_DISABLE))
+ return false;
+ else if (event_flags == cpu_to_vhost16(vq, RING_EVENT_FLAGS_ENABLE))
+ return true;
+
+ /* Read desc event flags before event_off and event_wrap */
+ smp_rmb();
+
+ if (vhost_get_avail(vq, event_off_wrap,
+ &vq->driver_event->off_warp) < 0) {
+ vq_err(vq, "Failed to get driver desc_event_off/wrap");
+ return true;
+ }
+
+ off_wrap = vhost16_to_cpu(vq, event_off_wrap);
+
+ old = vq->signalled_used;
+ v = vq->signalled_used_valid;
+ new = vq->signalled_used = vq->last_used_idx;
+ vq->signalled_used_valid = true;
We should move those idx tracking before checking event_flags. Otherwise
we may lose interrupts because of a wrong signalled_used value.
Thanks
+
+ if (unlikely(!v))
+ return true;
+
+ return vhost_vring_packed_need_event(vq, off_wrap, new, old);
+}
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