linux-kernel - Re: [PATCH] virtio_ring: Fix querying of maximum DMA mapping size for virtio device

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Message-ID: <a39f8dff-8be5-c739-d0eb-7cdab3b76a05@arm.com>
Date:   Fri, 3 Dec 2021 15:50:41 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Will Deacon <will@...nel.org>,
        virtualization@...ts.linux-foundation.org
Cc:     linux-kernel@...r.kernel.org, Marc Zyngier <maz@...nel.org>,
        Quentin Perret <qperret@...gle.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>
Subject: Re: [PATCH] virtio_ring: Fix querying of maximum DMA mapping size for
 virtio device

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@...nel.org>
> Cc: Quentin Perret <qperret@...gle.com>
> Cc: "Michael S. Tsirkin" <mst@...hat.com>
> Cc: Jason Wang <jasowang@...hat.com>
> Signed-off-by: Will Deacon <will@...nel.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@....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;
>   }
>