Re: [PATCH 6/8] dma-mapping: fail early if physical address is mapped through platform callback

[Robin Murphy <robin.murphy@arm.com>]

On 2025-06-25 2:19 pm, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@nvidia.com>
> 
> All platforms which implement map_page interface don't support physical
> addresses without real struct page. Add condition to check it.

As-is, the condition also needs to cover iommu-dma, because that also 
still doesn't support non-page-backed addresses. You can't just do a 
simple s/page/phys/ rename and hope it's OK because you happen to get 
away with it for coherent, 64-bit, trusted devices.

Thanks,
Robin.

> Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
> ---
>   kernel/dma/mapping.c | 15 ++++++++++++++-
>   1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
> index 709405d46b2b..74efb6909103 100644
> --- a/kernel/dma/mapping.c
> +++ b/kernel/dma/mapping.c
> @@ -158,6 +158,7 @@ dma_addr_t dma_map_page_attrs(struct device *dev, struct page *page,
>   {
>   	const struct dma_map_ops *ops = get_dma_ops(dev);
>   	phys_addr_t phys = page_to_phys(page) + offset;
> +	bool is_pfn_valid = true;
>   	dma_addr_t addr;
>   
>   	BUG_ON(!valid_dma_direction(dir));
> @@ -170,8 +171,20 @@ dma_addr_t dma_map_page_attrs(struct device *dev, struct page *page,
>   		addr = dma_direct_map_phys(dev, phys, size, dir, attrs);
>   	else if (use_dma_iommu(dev))
>   		addr = iommu_dma_map_phys(dev, phys, size, dir, attrs);
> -	else
> +	else {
> +		if (IS_ENABLED(CONFIG_DMA_API_DEBUG))
> +			is_pfn_valid = pfn_valid(PHYS_PFN(phys));
> +
> +		if (unlikely(!is_pfn_valid))
> +			return DMA_MAPPING_ERROR;
> +
> +		/*
> +		 * All platforms which implement .map_page() don't support
> +		 * non-struct page backed addresses.
> +		 */
>   		addr = ops->map_page(dev, page, offset, size, dir, attrs);
> +	}
> +
>   	kmsan_handle_dma(phys, size, dir);
>   	trace_dma_map_phys(dev, phys, addr, size, dir, attrs);
>   	debug_dma_map_phys(dev, phys, size, dir, addr, attrs);