[RFC PATCH v2 7/7] Revert "virtio_ring: enable premapped mode whatever use_dma_api"

["Michael S. Tsirkin" <mst@xxxxxxxxxx>]

This reverts commit f9dac92ba9081062a6477ee015bd3b8c5914efc4.

leads to crashes with no ACCESS_PLATFORM when
sysctl net.core.high_order_alloc_disable=1

Cc: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
Reported-by: Si-Wei Liu <si-wei.liu@xxxxxxxxxx>
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
 drivers/virtio/virtio_ring.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index be7309b1e860..06b5bdf0920e 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -2782,7 +2782,7 @@ EXPORT_SYMBOL_GPL(virtqueue_resize);
  *
  * Returns zero or a negative error.
  * 0: success.
- * -EINVAL: too late to enable premapped mode, the vq already contains buffers.
+ * -EINVAL: vring does not use the dma api, so we can not enable premapped mode.
  */
 int virtqueue_set_dma_premapped(struct virtqueue *_vq)
 {
@@ -2798,6 +2798,11 @@ int virtqueue_set_dma_premapped(struct virtqueue *_vq)
 		return -EINVAL;
 	}
 
+	if (!vq->use_dma_api) {
+		END_USE(vq);
+		return -EINVAL;
+	}
+
 	vq->premapped = true;
 	vq->do_unmap = false;
 
-- 
MST