[RFC PATCH v2 4/5] vhost: push features to backend on force_modern

[Halil Pasic]

In vhost we don't push the features to the vhost device when the
features are set, but when the vhost device is started. This can
lead to problems when config space is implemented in the vhost
device, and the driver does some early config space reading (early in a
sense that it precedes setting FEATURES_OK).

Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
---
 hw/virtio/vhost.c         | 17 +++++++++++++++++
 include/hw/virtio/vhost.h |  2 ++
 2 files changed, 19 insertions(+)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index b4b29413e6..5764970298 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -1628,6 +1628,23 @@ void vhost_dev_free_inflight(struct vhost_inflight 
*inflight)
     }
 }
 
+int vhost_dev_force_modern(struct vhost_dev *hdev)
+{
+    uint64_t features;
+    int r;
+
+    assert(hdev->vhost_ops);
+
+    hdev->acked_features |= (0x1ULL << VIRTIO_F_VERSION_1);
+    features = hdev->acked_features;
+    r = hdev->vhost_ops->vhost_set_features(hdev, features);
+    if (r < 0) {
+        VHOST_OPS_DEBUG("vhost_set_features failed");
+        return -errno;
+    }
+    return 0;
+}
+
 static int vhost_dev_resize_inflight(struct vhost_inflight *inflight,
                                      uint64_t new_size)
 {
diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
index 1a9fc65089..9ef784e2e9 100644
--- a/include/hw/virtio/vhost.h
+++ b/include/hw/virtio/vhost.h
@@ -138,6 +138,8 @@ int vhost_dev_get_config(struct vhost_dev *hdev, uint8_t 
*config,
                          uint32_t config_len, Error **errp);
 int vhost_dev_set_config(struct vhost_dev *dev, const uint8_t *data,
                          uint32_t offset, uint32_t size, uint32_t flags);
+
+int vhost_dev_force_modern(struct vhost_dev *vdev);
 /* notifier callback in case vhost device config space changed
  */
 void vhost_dev_set_config_notifier(struct vhost_dev *dev,
-- 
2.25.1