[V5,4/6] virtio: event suppression support for packed ring

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 4105fe2448..a70551d26d 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -236,6 +236,44 @@  static void vring_split_desc_read(VirtIODevice *vdev, VRingDesc *desc,
     virtio_tswap16s(vdev, &desc->next);
 }
 
+static void vring_packed_event_read(VirtIODevice *vdev,
+                                    MemoryRegionCache *cache,
+                                    VRingPackedDescEvent *e)
+{
+    hwaddr off_off = offsetof(VRingPackedDescEvent, off_wrap);
+    hwaddr off_flags = offsetof(VRingPackedDescEvent, flags);
+
+    address_space_read_cached(cache, off_flags, &e->flags,
+                              sizeof(e->flags));
+    /* Make sure flags is seen before off_wrap */
+    smp_rmb();
+    address_space_read_cached(cache, off_off, &e->off_wrap,
+                              sizeof(e->off_wrap));
+    virtio_tswap16s(vdev, &e->off_wrap);
+    virtio_tswap16s(vdev, &e->flags);
+}
+
+static void vring_packed_off_wrap_write(VirtIODevice *vdev,
+                                        MemoryRegionCache *cache,
+                                        uint16_t off_wrap)
+{
+    hwaddr off = offsetof(VRingPackedDescEvent, off_wrap);
+
+    virtio_tswap16s(vdev, &off_wrap);
+    address_space_write_cached(cache, off, &off_wrap, sizeof(off_wrap));
+    address_space_cache_invalidate(cache, off, sizeof(off_wrap));
+}
+
+static void vring_packed_flags_write(VirtIODevice *vdev,
+                                     MemoryRegionCache *cache, uint16_t flags)
+{
+    hwaddr off = offsetof(VRingPackedDescEvent, flags);
+
+    virtio_tswap16s(vdev, &flags);
+    address_space_write_cached(cache, off, &flags, sizeof(flags));
+    address_space_cache_invalidate(cache, off, sizeof(flags));
+}
+
 static VRingMemoryRegionCaches *vring_get_region_caches(struct VirtQueue *vq)
 {
     VRingMemoryRegionCaches *caches = atomic_rcu_read(&vq->vring.caches);
@@ -342,14 +380,8 @@  static inline void vring_set_avail_event(VirtQueue *vq, uint16_t val)
     address_space_cache_invalidate(&caches->used, pa, sizeof(val));
 }
 
-void virtio_queue_set_notification(VirtQueue *vq, int enable)
+static void virtio_queue_split_set_notification(VirtQueue *vq, int enable)
 {
-    vq->notification = enable;
-
-    if (!vq->vring.desc) {
-        return;
-    }
-
     rcu_read_lock();
     if (virtio_vdev_has_feature(vq->vdev, VIRTIO_RING_F_EVENT_IDX)) {
         vring_set_avail_event(vq, vring_avail_idx(vq));
@@ -365,6 +397,51 @@  void virtio_queue_set_notification(VirtQueue *vq, int enable)
     rcu_read_unlock();
 }
 
+static void virtio_queue_packed_set_notification(VirtQueue *vq, int enable)
+{
+    uint16_t off_wrap;
+    VRingPackedDescEvent e;
+    VRingMemoryRegionCaches *caches;
+
+    rcu_read_lock();
+    caches  = vring_get_region_caches(vq);
+    vring_packed_event_read(vq->vdev, &caches->used, &e);
+
+    if (!enable) {
+        e.flags = VRING_PACKED_EVENT_FLAG_DISABLE;
+    } else if (virtio_vdev_has_feature(vq->vdev, VIRTIO_RING_F_EVENT_IDX)) {
+        off_wrap = vq->shadow_avail_idx | vq->shadow_avail_wrap_counter << 15;
+        vring_packed_off_wrap_write(vq->vdev, &caches->used, off_wrap);
+        /* Make sure off_wrap is wrote before flags */
+        smp_wmb();
+        e.flags = VRING_PACKED_EVENT_FLAG_DESC;
+    } else {
+        e.flags = VRING_PACKED_EVENT_FLAG_ENABLE;
+    }
+
+    vring_packed_flags_write(vq->vdev, &caches->used, e.flags);
+    if (enable) {
+        /* Expose avail event/used flags before caller checks the avail idx. */
+        smp_mb();
+    }
+    rcu_read_unlock();
+}
+
+void virtio_queue_set_notification(VirtQueue *vq, int enable)
+{
+    vq->notification = enable;
+
+    if (!vq->vring.desc) {
+        return;
+    }
+
+    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
+        virtio_queue_packed_set_notification(vq, enable);
+    } else {
+        virtio_queue_split_set_notification(vq, enable);
+    }
+}
+
 int virtio_queue_ready(VirtQueue *vq)
 {
     return vq->vring.avail != 0;
@@ -2286,8 +2363,7 @@  static void virtio_set_isr(VirtIODevice *vdev, int value)
     }
 }
 
-/* Called within rcu_read_lock().  */
-static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq)
+static bool virtio_split_should_notify(VirtIODevice *vdev, VirtQueue *vq)
 {
     uint16_t old, new;
     bool v;
@@ -2310,6 +2386,54 @@  static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq)
     return !v || vring_need_event(vring_get_used_event(vq), new, old);
 }
 
+static bool vring_packed_need_event(VirtQueue *vq, bool wrap,
+                                    uint16_t off_wrap, uint16_t new,
+                                    uint16_t old)
+{
+    int off = off_wrap & ~(1 << 15);
+
+    if (wrap != off_wrap >> 15) {
+        off -= vq->vring.num;
+    }
+
+    return vring_need_event(off, new, old);
+}
+
+static bool virtio_packed_should_notify(VirtIODevice *vdev, VirtQueue *vq)
+{
+    VRingPackedDescEvent e;
+    uint16_t old, new;
+    bool v;
+    VRingMemoryRegionCaches *caches;
+
+    caches = vring_get_region_caches(vq);
+    vring_packed_event_read(vdev, &caches->avail, &e);
+
+    old = vq->signalled_used;
+    new = vq->signalled_used = vq->used_idx;
+    v = vq->signalled_used_valid;
+    vq->signalled_used_valid = true;
+
+    if (e.flags == VRING_PACKED_EVENT_FLAG_DISABLE) {
+        return false;
+    } else if (e.flags == VRING_PACKED_EVENT_FLAG_ENABLE) {
+        return true;
+    }
+
+    return !v || vring_packed_need_event(vq, vq->used_wrap_counter,
+                                         e.off_wrap, new, old);
+}
+
+/* Called within rcu_read_lock().  */
+static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq)
+{
+    if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
+        return virtio_packed_should_notify(vdev, vq);
+    } else {
+        return virtio_split_should_notify(vdev, vq);
+    }
+}
+
 void virtio_notify_irqfd(VirtIODevice *vdev, VirtQueue *vq)
 {
     bool should_notify;