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SubjectRe: [PATCH v6 3/7] dma-iommu: skip extra sync during unmap w/swiotlb
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On 2021-08-17 02:38, David Stevens wrote:
> From: David Stevens <stevensd@chromium.org>
>
> Calling the iommu_dma_sync_*_for_cpu functions during unmap can cause
> two copies out of the swiotlb buffer. Do the arch sync directly in
> __iommu_dma_unmap_swiotlb instead to avoid this. This makes the call to
> iommu_dma_sync_sg_for_cpu for untrusted devices in iommu_dma_unmap_sg no
> longer necessary, so move that invocation later in the function.

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

> Signed-off-by: David Stevens <stevensd@chromium.org>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> ---
> drivers/iommu/dma-iommu.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 8098ce593640..5dd2c517dbf5 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -504,6 +504,9 @@ static void __iommu_dma_unmap_swiotlb(struct device *dev, dma_addr_t dma_addr,
> if (WARN_ON(!phys))
> return;
>
> + if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) && !dev_is_dma_coherent(dev))
> + arch_sync_dma_for_cpu(phys, size, dir);
> +
> __iommu_dma_unmap(dev, dma_addr, size);
>
> if (unlikely(is_swiotlb_buffer(phys)))
> @@ -853,8 +856,6 @@ static dma_addr_t iommu_dma_map_page(struct device *dev, struct page *page,
> static void iommu_dma_unmap_page(struct device *dev, dma_addr_t dma_handle,
> size_t size, enum dma_data_direction dir, unsigned long attrs)
> {
> - if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
> - iommu_dma_sync_single_for_cpu(dev, dma_handle, size, dir);
> __iommu_dma_unmap_swiotlb(dev, dma_handle, size, dir, attrs);
> }
>
> @@ -1062,14 +1063,14 @@ static void iommu_dma_unmap_sg(struct device *dev, struct scatterlist *sg,
> struct scatterlist *tmp;
> int i;
>
> - if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
> - iommu_dma_sync_sg_for_cpu(dev, sg, nents, dir);
> -
> if (dev_is_untrusted(dev)) {
> iommu_dma_unmap_sg_swiotlb(dev, sg, nents, dir, attrs);
> return;
> }
>
> + if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
> + iommu_dma_sync_sg_for_cpu(dev, sg, nents, dir);
> +
> /*
> * The scatterlist segments are mapped into a single
> * contiguous IOVA allocation, so this is incredibly easy.
>

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