Re: [RFC PATCH V2 8/8] vhost: event suppression for packed ring

+
+static bool vhost_notify_packed(struct vhost_dev *dev,
+				struct vhost_virtqueue *vq)
+{
+	__virtio16 event_off_wrap, event_flags;
+	__u16 old, new;
+	bool v, wrap;
+	int off;
+
+	/* 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->desc_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_DESC)))
+		return event_flags ==
+		       cpu_to_vhost16(vq, RING_EVENT_FLAGS_ENABLE);

+
+	/* Read desc event flags before event_off and event_wrap */
+	smp_rmb();
+
+	if (vhost_get_avail(vq, event_off_wrap,
+			    &vq->driver_event->desc_event_off_warp) < 0) {
+		vq_err(vq, "Failed to get driver desc_event_off/wrap");
+		return true;
+	}
+
+	off = vhost16_to_cpu(vq, event_off_wrap);
+
+	wrap = off & 0x1;
+	off >>= 1;

+
+
+	old = vq->signalled_used;
+	v = vq->signalled_used_valid;
+	new = vq->signalled_used = vq->last_used_idx;
+	vq->signalled_used_valid = true;
+
+	if (unlikely(!v))
+		return true;
+
+	return vhost_vring_packed_need_event(vq, new, old, off) &&
+	       wrap == vq->used_wrap_counter;
+}
+
+static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
+{
+	if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED))
+		return vhost_notify_packed(dev, vq);
+	else
+		return vhost_notify_split(dev, vq);
+}
+
 /* This actually signals the guest, using eventfd. */
 void vhost_signal(struct vhost_dev *dev, struct vhost_virtqueue *vq)
 {

@@ -2789,7 +2911,17 @@ static bool vhost_enable_notify_packed(struct vhost_dev *dev,
 	__virtio16 flags;
 	int ret;
 
-	/* FIXME: disable notification through device area */
+	if (!(vq->used_flags & VRING_USED_F_NO_NOTIFY))
+		return false;
+	vq->used_flags &= ~VRING_USED_F_NO_NOTIFY;
+
+	flags = cpu_to_vhost16(vq, RING_EVENT_FLAGS_ENABLE);
+	ret = vhost_update_device_flags(vq, flags);
+	if (ret) {
+		vq_err(vq, "Failed to enable notification at %p: %d\n",
+		       &vq->device_event->desc_event_flags, ret);
+		return false;
+	}
 
 	/* They could have slipped one in as we were doing that: make
 	 * sure it's written, then check again. */

@@ -2855,7 +2987,18 @@ EXPORT_SYMBOL_GPL(vhost_enable_notify);
 static void vhost_disable_notify_packed(struct vhost_dev *dev,
 					struct vhost_virtqueue *vq)
 {
-	/* FIXME: disable notification through device area */
+	__virtio16 flags;
+	int r;
+
+	if (vq->used_flags & VRING_USED_F_NO_NOTIFY)
+		return;
+	vq->used_flags |= VRING_USED_F_NO_NOTIFY;
+
+	flags = cpu_to_vhost16(vq, RING_EVENT_FLAGS_DISABLE);
+	r = vhost_update_device_flags(vq, flags);
+	if (r)
+		vq_err(vq, "Failed to enable notification at %p: %d\n",
+		       &vq->device_event->desc_event_flags, r);
 }
 
 static void vhost_disable_notify_split(struct vhost_dev *dev,

diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 8a9df4f..02d7a36 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h

@@ -96,8 +96,14 @@ struct vhost_virtqueue {
 		struct vring_desc __user *desc;
 		struct vring_desc_packed __user *desc_packed;

 	};
-	struct vring_avail __user *avail;
-	struct vring_used __user *used;
+	union {
+		struct vring_avail __user *avail;
+		struct vring_packed_desc_event __user *driver_event;
+	};
+	union {
+		struct vring_used __user *used;
+		struct vring_packed_desc_event __user *device_event;
+	};
 	const struct vhost_umem_node *meta_iotlb[VHOST_NUM_ADDRS];
 	struct file *kick;
 	struct eventfd_ctx *call_ctx;

diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
index e297580..7cdbf06 100644
--- a/include/uapi/linux/virtio_ring.h
+++ b/include/uapi/linux/virtio_ring.h

@@ -75,6 +75,25 @@ struct vring_desc_packed {
 	__virtio16 flags;
 };
 
+/* Enable events */
+#define RING_EVENT_FLAGS_ENABLE 0x0
+/* Disable events */
+#define RING_EVENT_FLAGS_DISABLE 0x1
+/*
+ * Enable events for a specific descriptor
+ * (as specified by Descriptor Ring Change Event Offset/Wrap Counter).
+ * Only valid if VIRTIO_F_RING_EVENT_IDX has been negotiated.
+ */
+#define RING_EVENT_FLAGS_DESC 0x2
+/* The value 0x3 is reserved */
+
+struct vring_packed_desc_event {
+	/* Descriptor Ring Change Event Offset and Wrap Counter */
+	__virtio16 desc_event_off_warp;
+	/* Descriptor Ring Change Event Flags */
+	__virtio16 desc_event_flags;