vhost: init used ring after backend was set

Move the used ring initialization after backend was set. This
makes it possible to disable the backend and tweak the used ring,
then restart. This will also make it possible to log the used ring
write correctly.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 6 insertions, 8 deletions

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 5ef2f62becf4..9a108038fe52 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -629,15 +629,17 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
         return 0;
 }
 
-static int init_used(struct vhost_virtqueue *vq,
-                     struct vring_used __user *used)
+int vhost_init_used(struct vhost_virtqueue *vq)
 {
-        int r = put_user(vq->used_flags, &used->flags);
+        int r;
+        if (!vq->private_data)
+                return 0;
 
+        r = put_user(vq->used_flags, &vq->used->flags);
         if (r)
                 return r;
         vq->signalled_used_valid = false;
-        return get_user(vq->last_used_idx, &used->idx);
+        return get_user(vq->last_used_idx, &vq->used->idx);
 }
 
 static long vhost_set_vring(struct vhost_dev *d, int ioctl, void __user *argp)
@@ -752,10 +754,6 @@ static long vhost_set_vring(struct vhost_dev *d, int ioctl, void __user *argp)
                         }
                 }
 
-                r = init_used(vq, (struct vring_used __user *)(unsigned long)
-                              a.used_user_addr);
-                if (r)
-                        break;
                 vq->log_used = !!(a.flags & (0x1 << VHOST_VRING_F_LOG));
                 vq->desc = (void __user *)(unsigned long)a.desc_user_addr;
                 vq->avail = (void __user *)(unsigned long)a.avail_user_addr;