[PATCH 2/2] arm64/dma-mapping: validate dma_masks against IORT defined limits

[Robin Murphy]

Hi Nate,

On 31/01/17 20:16, Nate Watterson wrote:
> Some drivers set the dma_mask of client devices based solely on values
> read from capability registers which may not account for platform
> specific bus address width limitations. Fortunately, the ACPI IORT table
> provides a way to report the effective number of address bits a device
> can use to access memory. This information, when present, is used to
> supplement the checks already being done in dma_supported() to avoid
> setting overly generous dma_masks.

This is equally a problem for DT, and I think in general we'd prefer not
to be dragging ACPI/DT specifics in at this level when there's a clean
way to address it more generally. There is some recent ongoing
discussion and work in this area (latest part at [1]) - I have a local
branch somewhere implementing the stricter "don't special case default
masks" version (after I came around to Arnd's viewpoint), which I must
refresh myself on because there was some anomaly in the core DT code
which that brought to light.

> Signed-off-by: Nate Watterson <nwatters at codeaurora.org>
> ---
>  arch/arm64/mm/dma-mapping.c | 20 +++++++++++++++++++-
>  1 file changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
> index e040827..467fd23 100644
> --- a/arch/arm64/mm/dma-mapping.c
> +++ b/arch/arm64/mm/dma-mapping.c
> @@ -19,6 +19,7 @@
>  
>  #include <linux/gfp.h>
>  #include <linux/acpi.h>
> +#include <linux/acpi_iort.h>
>  #include <linux/bootmem.h>
>  #include <linux/cache.h>
>  #include <linux/export.h>
> @@ -347,6 +348,12 @@ static int __swiotlb_get_sgtable(struct device *dev, struct sg_table *sgt,
>  
>  static int __swiotlb_dma_supported(struct device *hwdev, u64 mask)
>  {
> +	int dma_limit;
> +
> +	dma_limit = iort_get_memory_address_limit(hwdev);
> +	if (dma_limit >= 0 && DMA_BIT_MASK(dma_limit) < mask)
> +		return 0;
> +
>  	if (swiotlb)
>  		return swiotlb_dma_supported(hwdev, mask);
>  	return 1;
> @@ -784,6 +791,17 @@ static void __iommu_unmap_sg_attrs(struct device *dev,
>  	iommu_dma_unmap_sg(dev, sgl, nelems, dir, attrs);
>  }
>  
> +static int __iommu_dma_supported(struct device *hwdev, u64 mask)
> +{
> +	int dma_limit;
> +
> +	dma_limit = iort_get_memory_address_limit(hwdev);
> +	if (dma_limit >= 0 && DMA_BIT_MASK(dma_limit) < mask)
> +		return 0;
> +
> +	return iommu_dma_supported(hwdev, mask);

Either way, this reminds me that iommu_dma_supported() is another thing
I got completely wrong - time to write yet another patch...

Robin.

[1]:http://www.mail-archive.com/linux-renesas-soc@vger.kernel.org/msg10637.html

> +}
> +
>  static struct dma_map_ops iommu_dma_ops = {
>  	.alloc = __iommu_alloc_attrs,
>  	.free = __iommu_free_attrs,
> @@ -799,7 +817,7 @@ static void __iommu_unmap_sg_attrs(struct device *dev,
>  	.sync_sg_for_device = __iommu_sync_sg_for_device,
>  	.map_resource = iommu_dma_map_resource,
>  	.unmap_resource = iommu_dma_unmap_resource,
> -	.dma_supported = iommu_dma_supported,
> +	.dma_supported = __iommu_dma_supported,
>  	.mapping_error = iommu_dma_mapping_error,
>  };
>  
>