[PATCH] vdpa-dev: Fix initialisation order to restore VDUSE compatibility

[Kevin Wolf <kwolf@redhat.com>]

VDUSE requires that virtqueues are first enabled before the DRIVER_OK
status flag is set; with the current API of the kernel module, it is
impossible to enable the opposite order in our block export code because
userspace is not notified when a virtqueue is enabled.

This requirement also mathces the normal initialisation order as done by
the generic vhost code in QEMU. However, commit 6c482547 accidentally
changed the order for vdpa-dev and broke access to VDUSE devices with
this.

This changes vdpa-dev to use the normal order again and use the standard
vhost callback .vhost_set_vring_enable for this. VDUSE devices can be
used with vdpa-dev again after this fix.

Cc: qemu-stable@nongnu.org
Fixes: 6c4825476a4351530bcac17abab72295b75ffe98
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 hw/virtio/vdpa-dev.c   |  5 +----
 hw/virtio/vhost-vdpa.c | 17 +++++++++++++++++
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/hw/virtio/vdpa-dev.c b/hw/virtio/vdpa-dev.c
index eb9ecea83b..13e87f06f6 100644
--- a/hw/virtio/vdpa-dev.c
+++ b/hw/virtio/vdpa-dev.c
@@ -253,14 +253,11 @@ static int vhost_vdpa_device_start(VirtIODevice *vdev, Error **errp)
 
     s->dev.acked_features = vdev->guest_features;
 
-    ret = vhost_dev_start(&s->dev, vdev, false);
+    ret = vhost_dev_start(&s->dev, vdev, true);
     if (ret < 0) {
         error_setg_errno(errp, -ret, "Error starting vhost");
         goto err_guest_notifiers;
     }
-    for (i = 0; i < s->dev.nvqs; ++i) {
-        vhost_vdpa_set_vring_ready(&s->vdpa, i);
-    }
     s->started = true;
 
     /*
diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
index 3a43beb312..c4574d56c5 100644
--- a/hw/virtio/vhost-vdpa.c
+++ b/hw/virtio/vhost-vdpa.c
@@ -904,6 +904,22 @@ int vhost_vdpa_set_vring_ready(struct vhost_vdpa *v, unsigned idx)
     return r;
 }
 
+static int vhost_vdpa_set_vring_enable(struct vhost_dev *dev, int enable)
+{
+    struct vhost_vdpa *v = dev->opaque;
+    unsigned int i;
+    int ret;
+
+    for (i = 0; i < dev->nvqs; ++i) {
+        ret = vhost_vdpa_set_vring_ready(v, i);
+        if (ret < 0) {
+            return ret;
+        }
+    }
+
+    return 0;
+}
+
 static int vhost_vdpa_set_config_call(struct vhost_dev *dev,
                                        int fd)
 {
@@ -1524,6 +1540,7 @@ const VhostOps vdpa_ops = {
         .vhost_set_features = vhost_vdpa_set_features,
         .vhost_reset_device = vhost_vdpa_reset_device,
         .vhost_get_vq_index = vhost_vdpa_get_vq_index,
+        .vhost_set_vring_enable = vhost_vdpa_set_vring_enable,
         .vhost_get_config  = vhost_vdpa_get_config,
         .vhost_set_config = vhost_vdpa_set_config,
         .vhost_requires_shm_log = NULL,
-- 
2.43.0