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SubjectRe: [PATCH] intel-iommu: Obey coherent_dma_mask for alloc_coherent on passthrough
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On Wed, 04 Nov 2009 15:59:34 -0700
Alex Williamson <alex.williamson@hp.com> wrote:

> intel_alloc_coherent() needs to follow DMA mapping convention and
> make use of the coherent_dma_mask of the device for identity mappings.
> Without this, devices may get buffers they can't use. This patch
> provides best effort allocations and fails the request if the mask
> requirements are not met rather than returning an unusable buffer.
>
> Signed-off-by: Alex Williamson <alex.williamson@hp.com>
> ---
>
> This patch fixes a regression introduced since 2.6.31 that prevents
> devices with a restricted coherent_dma_mask from working in passthrough
> mode.
>
> drivers/pci/intel-iommu.c | 12 ++++++++++--
> 1 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
> index b1e97e6..8283df9 100644
> --- a/drivers/pci/intel-iommu.c
> +++ b/drivers/pci/intel-iommu.c
> @@ -2582,7 +2582,7 @@ static dma_addr_t __intel_map_single(struct device *hwdev, phys_addr_t paddr,
> BUG_ON(dir == DMA_NONE);
>
> if (iommu_no_mapping(hwdev))
> - return paddr;
> + return paddr + size > dma_mask ? 0 : paddr;

You can use dma_capable(hwdev, paddr, size) here.


> domain = get_valid_domain_for_dev(pdev);
> if (!domain)
> @@ -2767,7 +2767,15 @@ static void *intel_alloc_coherent(struct device *hwdev, size_t size,
>
> size = PAGE_ALIGN(size);
> order = get_order(size);
> - flags &= ~(GFP_DMA | GFP_DMA32);
> +
> + if (!iommu_no_mapping(hwdev))
> + flags &= ~(GFP_DMA | GFP_DMA32);
> + else if (hwdev->coherent_dma_mask != DMA_BIT_MASK(64)) {
> + if (hwdev->coherent_dma_mask < DMA_BIT_MASK(32))
> + flags |= GFP_DMA;
> + else
> + flags |= GFP_DMA32;
> + }

This is fine for 2.6.32 but we'll cleanly fix this by using
swiotlb_dma_ops later, right?


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