virtio: Honour 'may_reduce_num' in vring_create_virtqueue

commit cf94db21905333e610e479688add629397a4b384 upstream.

vring_create_virtqueue() allows the caller to specify via the
may_reduce_num parameter whether the vring code is allowed to
allocate a smaller ring than specified.

However, the split ring allocation code tries to allocate a
smaller ring on allocation failure regardless of what the
caller specified. This may cause trouble for e.g. virtio-pci
in legacy mode, which does not support ring resizing. (The
packed ring code does not resize in any case.)

Let's fix this by bailing out immediately in the split ring code
if the requested size cannot be allocated and may_reduce_num has
not been specified.

While at it, fix a typo in the usage instructions.

Fixes: 2a2d1382fe9d ("virtio: Add improved queue allocation API")
Cc: stable@vger.kernel.org # v4.6+
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
Reviewed-by: Jens Freimann <jfreimann@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 8977f40ea4417b2f8d2a5ef9c5eb883ba8a54f7f..2f09294c5946090c5f54e78b5f32ac2c07eeede8 100644 (file)
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1040,6 +1040,8 @@ struct virtqueue *vring_create_virtqueue(
                                          GFP_KERNEL|__GFP_NOWARN|__GFP_ZERO);
                if (queue)
                        break;
+               if (!may_reduce_num)
+                       return NULL;
        }
 
        if (!num)

diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index e8d36938f09a56cfe4729c17b0ee8175b4991bbe..b38c1871b7354455bed3657381159578189efcf3 100644 (file)
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -62,7 +62,7 @@ struct virtqueue;
 /*
  * Creates a virtqueue and allocates the descriptor ring.  If
  * may_reduce_num is set, then this may allocate a smaller ring than
- * expected.  The caller should query virtqueue_get_ring_size to learn
+ * expected.  The caller should query virtqueue_get_vring_size to learn
  * the actual size of the ring.
  */
 struct virtqueue *vring_create_virtqueue(unsigned int index,