virtio: event index support

Add support for event_idx feature, and utilize it to
reduce the number of interrupts and exits for the guest.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/hw/virtio.h b/hw/virtio.h
index bc722896c9..69e6bb1a4e 100644
--- a/hw/virtio.h
+++ b/hw/virtio.h
@@ -46,6 +46,11 @@
 #define VIRTIO_F_NOTIFY_ON_EMPTY        24
 /* We support indirect buffer descriptors */
 #define VIRTIO_RING_F_INDIRECT_DESC     28
+/* The Guest publishes the used index for which it expects an interrupt
+ * at the end of the avail ring. Host should ignore the avail->flags field. */
+/* The Host publishes the avail index for which it expects a kick
+ * at the end of the used ring. Guest should ignore the used->flags field. */
+#define VIRTIO_RING_F_EVENT_IDX         29
 /* A guest should never accept this.  It implies negotiation is broken. */
 #define VIRTIO_F_BAD_FEATURE		30
 
@@ -210,7 +215,9 @@ void virtio_serial_exit(VirtIODevice *vdev);
 
 #define DEFINE_VIRTIO_COMMON_FEATURES(_state, _field) \
 	DEFINE_PROP_BIT("indirect_desc", _state, _field, \
-			VIRTIO_RING_F_INDIRECT_DESC, true)
+			VIRTIO_RING_F_INDIRECT_DESC, true), \
+	DEFINE_PROP_BIT("event_idx", _state, _field, \
+			VIRTIO_RING_F_EVENT_IDX, true)
 
 target_phys_addr_t virtio_queue_get_desc_addr(VirtIODevice *vdev, int n);
 target_phys_addr_t virtio_queue_get_avail_addr(VirtIODevice *vdev, int n);