[PATCH v2 03/14] vhost: Add Shadow VirtQueue call forwarding capabilities

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

This will make qemu aware of the device used buffers, allowing it to
write the guest memory with its contents if needed.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/virtio/vhost-shadow-virtqueue.h |  4 ++++
 hw/virtio/vhost-shadow-virtqueue.c | 34 ++++++++++++++++++++++++++++++
 hw/virtio/vhost-vdpa.c             | 31 +++++++++++++++++++++++++--
 3 files changed, 67 insertions(+), 2 deletions(-)

diff --git a/hw/virtio/vhost-shadow-virtqueue.h b/hw/virtio/vhost-shadow-virtqueue.h
index 1cbc87d5d8..1d4c160d0a 100644
--- a/hw/virtio/vhost-shadow-virtqueue.h
+++ b/hw/virtio/vhost-shadow-virtqueue.h
@@ -28,9 +28,13 @@ typedef struct VhostShadowVirtqueue {
      * So shadow virtqueue must not clean it, or we would lose VirtQueue one.
      */
     EventNotifier svq_kick;
+
+    /* Guest's call notifier, where the SVQ calls guest. */
+    EventNotifier svq_call;
 } VhostShadowVirtqueue;
 
 void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd);
+void vhost_svq_set_guest_call_notifier(VhostShadowVirtqueue *svq, int call_fd);
 
 void vhost_svq_stop(VhostShadowVirtqueue *svq);
 
diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index a5d0659f86..54c701a196 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -23,6 +23,38 @@ static void vhost_handle_guest_kick(EventNotifier *n)
     event_notifier_set(&svq->hdev_kick);
 }
 
+/* Forward vhost notifications */
+static void vhost_svq_handle_call(EventNotifier *n)
+{
+    VhostShadowVirtqueue *svq = container_of(n, VhostShadowVirtqueue,
+                                             hdev_call);
+    event_notifier_test_and_clear(n);
+    event_notifier_set(&svq->svq_call);
+}
+
+/**
+ * Set the call notifier for the SVQ to call the guest
+ *
+ * @svq Shadow virtqueue
+ * @call_fd call notifier
+ *
+ * Called on BQL context.
+ */
+void vhost_svq_set_guest_call_notifier(VhostShadowVirtqueue *svq, int call_fd)
+{
+    if (call_fd == VHOST_FILE_UNBIND) {
+        /*
+         * Fail event_notifier_set if called handling device call.
+         *
+         * SVQ still needs device notifications, since it needs to keep
+         * forwarding used buffers even with the unbind.
+         */
+        memset(&svq->svq_call, 0, sizeof(svq->svq_call));
+    } else {
+        event_notifier_init_fd(&svq->svq_call, call_fd);
+    }
+}
+
 /**
  * Set a new file descriptor for the guest to kick the SVQ and notify for avail
  *
@@ -90,6 +122,7 @@ VhostShadowVirtqueue *vhost_svq_new(void)
     }
 
     event_notifier_init_fd(&svq->svq_kick, VHOST_FILE_UNBIND);
+    event_notifier_set_handler(&svq->hdev_call, vhost_svq_handle_call);
     return g_steal_pointer(&svq);
 
 err_init_hdev_call:
@@ -109,6 +142,7 @@ void vhost_svq_free(gpointer pvq)
     VhostShadowVirtqueue *vq = pvq;
     vhost_svq_stop(vq);
     event_notifier_cleanup(&vq->hdev_kick);
+    event_notifier_set_handler(&vq->hdev_call, NULL);
     event_notifier_cleanup(&vq->hdev_call);
     g_free(vq);
 }
diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
index 454bf50735..c73215751d 100644
--- a/hw/virtio/vhost-vdpa.c
+++ b/hw/virtio/vhost-vdpa.c
@@ -724,6 +724,13 @@ static int vhost_vdpa_set_vring_dev_kick(struct vhost_dev *dev,
     return vhost_vdpa_call(dev, VHOST_SET_VRING_KICK, file);
 }
 
+static int vhost_vdpa_set_vring_dev_call(struct vhost_dev *dev,
+                                         struct vhost_vring_file *file)
+{
+    trace_vhost_vdpa_set_vring_call(dev, file->index, file->fd);
+    return vhost_vdpa_call(dev, VHOST_SET_VRING_CALL, file);
+}
+
 /**
  * Set the shadow virtqueue descriptors to the device
  *
@@ -731,6 +738,9 @@ static int vhost_vdpa_set_vring_dev_kick(struct vhost_dev *dev,
  * @svq   The shadow virtqueue
  * @idx   The index of the virtqueue in the vhost device
  * @errp  Error
+ *
+ * Note that this function does not rewind kick file descriptor if cannot set
+ * call one.
  */
 static bool vhost_vdpa_svq_setup(struct vhost_dev *dev,
                                  VhostShadowVirtqueue *svq,
@@ -747,6 +757,14 @@ static bool vhost_vdpa_svq_setup(struct vhost_dev *dev,
     r = vhost_vdpa_set_vring_dev_kick(dev, &file);
     if (unlikely(r != 0)) {
         error_setg_errno(errp, -r, "Can't set device kick fd");
+        return false;
+    }
+
+    event_notifier = &svq->hdev_call;
+    file.fd = event_notifier_get_fd(event_notifier);
+    r = vhost_vdpa_set_vring_dev_call(dev, &file);
+    if (unlikely(r != 0)) {
+        error_setg_errno(errp, -r, "Can't set device call fd");
     }
 
     return r == 0;
@@ -872,8 +890,17 @@ static int vhost_vdpa_set_vring_kick(struct vhost_dev *dev,
 static int vhost_vdpa_set_vring_call(struct vhost_dev *dev,
                                        struct vhost_vring_file *file)
 {
-    trace_vhost_vdpa_set_vring_call(dev, file->index, file->fd);
-    return vhost_vdpa_call(dev, VHOST_SET_VRING_CALL, file);
+    struct vhost_vdpa *v = dev->opaque;
+
+    if (v->shadow_vqs_enabled) {
+        int vdpa_idx = file->index - dev->vq_index;
+        VhostShadowVirtqueue *svq = g_ptr_array_index(v->shadow_vqs, vdpa_idx);
+
+        vhost_svq_set_guest_call_notifier(svq, file->fd);
+        return 0;
+    } else {
+        return vhost_vdpa_set_vring_dev_call(dev, file);
+    }
 }
 
 static int vhost_vdpa_get_features(struct vhost_dev *dev,
-- 
2.27.0