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SubjectRe: [PATCH 2/2] virtio/virtio_ring: Fix the dma_max_mapping_size call
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On 22/07/2019 15:55, Eric Auger wrote:
> 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@redhat.com>
> Suggested-by: Christoph Hellwig <hch@lst.de>
> ---
> 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)

Hmm, might it make sense to roll that check up into vring_use_dma_api()
itself? After all, if the device has no mask then it's likely that other
DMA API ops wouldn't really work as expected either.

Robin.

> max_segment_size = dma_max_mapping_size(&vdev->dev);
>
> return max_segment_size;
>

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