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SubjectRe: [PATCH] virtio_ring: Fix querying of maximum DMA mapping size for virtio device
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On 01/12/2021 11:20, Will Deacon wrote:
> virtio_max_dma_size() returns the maximum DMA mapping size of the virtio
> device by querying dma_max_mapping_size() for the device when the DMA
> API is in use for the vring. Unfortunately, the device passed is
> initialised by register_virtio_device() and does not inherit the DMA
> configuration from its parent, resulting in SWIOTLB errors when bouncing
> is enabled and the default 256K mapping limit (IO_TLB_SEGSIZE) is not
> respected:
>
> | virtio-pci 0000:00:01.0: swiotlb buffer is full (sz: 294912 bytes), total 1024 (slots), used 725 (slots)
>
> Follow the pattern used elsewhere in the virtio_ring code when calling
> into the DMA layer and pass the parent device to dma_max_mapping_size()
> instead.
>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Quentin Perret <qperret@google.com>
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Cc: Jason Wang <jasowang@redhat.com>
> Signed-off-by: Will Deacon <will@kernel.org>

We hit a similar problem and ended up in the same patch, a bit late [0].

FWIW:

Tested-by: Suzuki K Poulose <suzuki.poulose@arm.com>

[0]
https://lkml.kernel.org/r/20211203121614.3380162-1-suzuki.poulose@arm.com


> ---
> 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 6d2614e34470..028b05d44546 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -268,7 +268,7 @@ size_t virtio_max_dma_size(struct virtio_device *vdev)
> size_t max_segment_size = SIZE_MAX;
>
> if (vring_use_dma_api(vdev))
> - max_segment_size = dma_max_mapping_size(&vdev->dev);
> + max_segment_size = dma_max_mapping_size(vdev->dev.parent);
>
> return max_segment_size;
> }
>

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