[RFC v3 08/29] vhost: Route host->guest notification through shadow virtqueue

["Eugenio Pérez" <eperezma@redhat.com>]

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/virtio/vhost-shadow-virtqueue.h |  3 +
 include/hw/virtio/vhost.h          |  1 +
 hw/virtio/vhost-shadow-virtqueue.c | 95 ++++++++++++++++++++++++++++++
 hw/virtio/vhost.c                  | 15 +++++
 4 files changed, 114 insertions(+)

diff --git a/hw/virtio/vhost-shadow-virtqueue.h b/hw/virtio/vhost-shadow-virtqueue.h
index c891c6510d..2ca4b92b12 100644
--- a/hw/virtio/vhost-shadow-virtqueue.h
+++ b/hw/virtio/vhost-shadow-virtqueue.h
@@ -17,6 +17,9 @@
 
 typedef struct VhostShadowVirtqueue VhostShadowVirtqueue;
 
+void vhost_shadow_vq_mask(VhostShadowVirtqueue *svq, EventNotifier *masked);
+void vhost_shadow_vq_unmask(VhostShadowVirtqueue *svq);
+
 bool vhost_shadow_vq_start(struct vhost_dev *dev,
                            unsigned idx,
                            VhostShadowVirtqueue *svq);
diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
index 7ffdf9aea0..67cedf83da 100644
--- a/include/hw/virtio/vhost.h
+++ b/include/hw/virtio/vhost.h
@@ -28,6 +28,7 @@ struct vhost_virtqueue {
     unsigned avail_size;
     unsigned long long used_phys;
     unsigned used_size;
+    /* Access/writing to notifier_is_masked is protected by BQL */
     bool notifier_is_masked;
     EventNotifier masked_notifier;
     struct vhost_dev *dev;
diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index 3e43399e9c..7d76e271a5 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -32,8 +32,16 @@ typedef struct VhostShadowVirtqueue {
      */
     EventNotifier host_notifier;
 
+    /* (Possible) masked notifier */
+    struct {
+        EventNotifier *n;
+    } masked_notifier;
+
     /* Virtio queue shadowing */
     VirtQueue *vq;
+
+    /* Virtio device */
+    VirtIODevice *vdev;
 } VhostShadowVirtqueue;
 
 /* Forward guest notifications */
@@ -49,6 +57,58 @@ static void vhost_handle_guest_kick(EventNotifier *n)
     event_notifier_set(&svq->kick_notifier);
 }
 
+/* Forward vhost notifications */
+static void vhost_shadow_vq_handle_call_no_test(EventNotifier *n)
+{
+    VhostShadowVirtqueue *svq = container_of(n, VhostShadowVirtqueue,
+                                             call_notifier);
+    EventNotifier *masked_notifier;
+
+    masked_notifier = svq->masked_notifier.n;
+
+    if (!masked_notifier) {
+        unsigned n = virtio_get_queue_index(svq->vq);
+        virtio_queue_invalidate_signalled_used(svq->vdev, n);
+        virtio_notify_irqfd(svq->vdev, svq->vq);
+    } else {
+        event_notifier_set(svq->masked_notifier.n);
+    }
+}
+
+static void vhost_shadow_vq_handle_call(EventNotifier *n)
+{
+    if (likely(event_notifier_test_and_clear(n))) {
+        vhost_shadow_vq_handle_call_no_test(n);
+    }
+}
+
+/*
+ * Mask the shadow virtqueue.
+ *
+ * It can be called from a guest masking vmexit or shadow virtqueue start
+ * through QMP.
+ *
+ * @vq Shadow virtqueue
+ * @masked Masked notifier to signal instead of guest
+ */
+void vhost_shadow_vq_mask(VhostShadowVirtqueue *svq, EventNotifier *masked)
+{
+    svq->masked_notifier.n = masked;
+}
+
+/*
+ * Unmask the shadow virtqueue.
+ *
+ * It can be called from a guest unmasking vmexit or shadow virtqueue start
+ * through QMP.
+ *
+ * @vq Shadow virtqueue
+ */
+void vhost_shadow_vq_unmask(VhostShadowVirtqueue *svq)
+{
+    svq->masked_notifier.n = NULL;
+}
+
 /*
  * Restore the vhost guest to host notifier, i.e., disables svq effect.
  */
@@ -103,8 +163,33 @@ bool vhost_shadow_vq_start(struct vhost_dev *dev,
         goto err_set_vring_kick;
     }
 
+    /* Set vhost call */
+    file.fd = event_notifier_get_fd(&svq->call_notifier),
+    r = dev->vhost_ops->vhost_set_vring_call(dev, &file);
+    if (unlikely(r != 0)) {
+        error_report("Couldn't set call fd: %s", strerror(errno));
+        goto err_set_vring_call;
+    }
+
+    /* Set shadow vq -> guest notifier */
+    assert(dev->shadow_vqs_enabled);
+    vhost_virtqueue_mask(dev, dev->vdev, dev->vq_index + idx,
+                         dev->vqs[idx].notifier_is_masked);
+
+    if (dev->vqs[idx].notifier_is_masked &&
+               event_notifier_test_and_clear(&dev->vqs[idx].masked_notifier)) {
+        /* Check for pending notifications from the device */
+        vhost_shadow_vq_handle_call_no_test(&svq->call_notifier);
+    }
+
     return true;
 
+err_set_vring_call:
+    r = vhost_shadow_vq_restore_vdev_host_notifier(dev, idx, svq);
+    if (unlikely(r < 0)) {
+        error_report("Couldn't restore vq kick fd: %s", strerror(-r));
+    }
+
 err_set_vring_kick:
     event_notifier_set_handler(&svq->host_notifier, NULL);
 
@@ -126,7 +211,13 @@ void vhost_shadow_vq_stop(struct vhost_dev *dev,
         error_report("Couldn't restore vq kick fd: %s", strerror(-r));
     }
 
+    assert(!dev->shadow_vqs_enabled);
+
     event_notifier_set_handler(&svq->host_notifier, NULL);
+
+    /* Restore vhost call */
+    vhost_virtqueue_mask(dev, dev->vdev, dev->vq_index + idx,
+                         dev->vqs[idx].notifier_is_masked);
 }
 
 /*
@@ -154,6 +245,9 @@ VhostShadowVirtqueue *vhost_shadow_vq_new(struct vhost_dev *dev, int idx)
     }
 
     svq->vq = virtio_get_queue(dev->vdev, vq_idx);
+    svq->vdev = dev->vdev;
+    event_notifier_set_handler(&svq->call_notifier,
+                               vhost_shadow_vq_handle_call);
     return g_steal_pointer(&svq);
 
 err_init_call_notifier:
@@ -169,6 +263,7 @@ err_init_kick_notifier:
 void vhost_shadow_vq_free(VhostShadowVirtqueue *vq)
 {
     event_notifier_cleanup(&vq->kick_notifier);
+    event_notifier_set_handler(&vq->call_notifier, NULL);
     event_notifier_cleanup(&vq->call_notifier);
     g_free(vq);
 }
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 84091b5251..9c9c63345b 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -1591,6 +1591,21 @@ void vhost_virtqueue_mask(struct vhost_dev *hdev, VirtIODevice *vdev, int n,
     /* should only be called after backend is connected */
     assert(hdev->vhost_ops);
 
+    if (hdev->shadow_vqs_enabled) {
+        if (mask) {
+            vhost_shadow_vq_mask(hdev->shadow_vqs[index],
+                                 &hdev->vqs[index].masked_notifier);
+        } else {
+            vhost_shadow_vq_unmask(hdev->shadow_vqs[index]);
+        }
+
+        /*
+         * Vhost call fd must remain the same since shadow vq is not polling
+         * for changes
+         */
+        return;
+    }
+
     if (mask) {
         assert(vdev->use_guest_notifier_mask);
         file.fd = event_notifier_get_fd(&hdev->vqs[index].masked_notifier);
-- 
2.27.0