[PATCH 2/2] virtio/virtio_ring: Fix the dma_max_mapping_size call

[Eric Auger]

Do not call dma_max_mapping_size for devices that have no DMA
mask set, otherwise we can hit a NULL pointer dereference.

This occurs when a virtio-blk-pci device is protected with
a virtual IOMMU.

Fixes: e6d6dd6c875e ("virtio: Introduce virtio_max_dma_size()")
Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>
Suggested-by: Christoph Hellwig <hch@xxxxxx>
---
 drivers/virtio/virtio_ring.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index c8be1c4f5b55..37c143971211 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -262,7 +262,7 @@ size_t virtio_max_dma_size(struct virtio_device *vdev)
 {
 	size_t max_segment_size = SIZE_MAX;
 
-	if (vring_use_dma_api(vdev))
+	if (vring_use_dma_api(vdev) && vdev->dev.dma_mask)
 		max_segment_size = dma_max_mapping_size(&vdev->dev);
 
 	return max_segment_size;
-- 
2.20.1