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

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Date:   Thu, 2 Dec 2021 11:12:25 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Will Deacon <will@...nel.org>
Cc:     virtualization <virtualization@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Marc Zyngier <maz@...nel.org>,
        Quentin Perret <qperret@...gle.com>,
        "Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH] virtio_ring: Fix querying of maximum DMA mapping size for
 virtio device

On Wed, Dec 1, 2021 at 7:20 PM Will Deacon <will@...nel.org> 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>

Acked-by: Jason Wang <jasowang@...hat.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;
>  }
> --
> 2.34.0.rc2.393.gf8c9666880-goog
>