[RFC PATCH 04/12] vdpa: delay set_vring_ready after DRIVER_OK

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

To restore the device in the destination of a live migration we send the
commands through control virtqueue. For a device to read CVQ it must
have received DRIVER_OK status bit.

However this open a window where the device could start receiving
packets in rx queue 0 before it receive the RSS configuration. To avoid
that, we will not send vring_enable until all configuration is used by
the device.

As a first step, reverse the DRIVER_OK and SET_VRING_ENABLE steps.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/virtio/vhost-vdpa.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
index 906c365036..1d8829c619 100644
--- a/hw/virtio/vhost-vdpa.c
+++ b/hw/virtio/vhost-vdpa.c
@@ -730,13 +730,18 @@ static int vhost_vdpa_get_vq_index(struct vhost_dev *dev, int idx)
     return idx;
 }
 
+/**
+ * Set ready all vring of the device
+ *
+ * @dev: Vhost device
+ */
 static int vhost_vdpa_set_vring_ready(struct vhost_dev *dev)
 {
     int i;
     trace_vhost_vdpa_set_vring_ready(dev);
-    for (i = 0; i < dev->nvqs; ++i) {
+    for (i = 0; i < dev->vq_index_end; ++i) {
         struct vhost_vring_state state = {
-            .index = dev->vq_index + i,
+            .index = i,
             .num = 1,
         };
         vhost_vdpa_call(dev, VHOST_VDPA_SET_VRING_ENABLE, &state);
@@ -1111,7 +1116,6 @@ static int vhost_vdpa_dev_start(struct vhost_dev *dev, bool started)
         if (unlikely(!ok)) {
             return -1;
         }
-        vhost_vdpa_set_vring_ready(dev);
     } else {
         ok = vhost_vdpa_svqs_stop(dev);
         if (unlikely(!ok)) {
@@ -1125,16 +1129,22 @@ static int vhost_vdpa_dev_start(struct vhost_dev *dev, bool started)
     }
 
     if (started) {
+        int r;
+
         memory_listener_register(&v->listener, &address_space_memory);
-        return vhost_vdpa_add_status(dev, VIRTIO_CONFIG_S_DRIVER_OK);
+        r = vhost_vdpa_add_status(dev, VIRTIO_CONFIG_S_DRIVER_OK);
+        if (unlikely(r)) {
+            return r;
+        }
+        vhost_vdpa_set_vring_ready(dev);
     } else {
         vhost_vdpa_reset_device(dev);
         vhost_vdpa_add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE |
                                    VIRTIO_CONFIG_S_DRIVER);
         memory_listener_unregister(&v->listener);
-
-        return 0;
     }
+
+    return 0;
 }
 
 static int vhost_vdpa_set_log_base(struct vhost_dev *dev, uint64_t base,
-- 
2.31.1