virtio/balloon: verify device has config space

Some devices might not implement config space access
(e.g. remoteproc used not to - before 3.9).
virtio/balloon needs config space access so make it
fail gracefully if not there.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 50c5f42d7a9f..3176ea4028a8 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -466,6 +466,12 @@ static int virtballoon_probe(struct virtio_device *vdev)
         struct virtio_balloon *vb;
         int err;
 
+        if (!vdev->config->get) {
+                dev_err(&vdev->dev, "%s failure: config access disabled\n",
+                        __func__);
+                return -EINVAL;
+        }
+
         vdev->priv = vb = kmalloc(sizeof(*vb), GFP_KERNEL);
         if (!vb) {
                 err = -ENOMEM;