dma-direct: relax addressability checks in dma_direct_supported (91ef26f9) · Commits · 戴 / test

dma_direct_supported tries to find the minimum addressable bitmask based on the end pfn and optional magic that architectures can use to communicate the size of the magic ZONE_DMA that can be used for bounce buffering. But between the DMA offsets that can change per device (or sometimes even region), the fact the ZONE_DMA isn't even guaranteed to be the lowest addresses and failure of having proper interfaces to the MM code this fails at least for one arm subarchitecture. As all the legacy DMA implementations have supported 32-bit DMA masks, and 32-bit masks are guranteed to always work by the API contract (using bounce buffers if needed), we can short cut the complicated check and always return true without breaking existing assumptions. Hopefully we can properly clean up the interaction with the arch defined zones and the bootmem allocator eventually. Fixes: ("arm: use swiotlb for bounce buffering on LPAE configs") Reported-by:

Peter Ujfalusi <peter.ujfalusi@ti.com> Signed-off-by:

Christoph Hellwig <hch@lst.de> Tested-by:

Peter Ujfalusi <peter.ujfalusi@ti.com>

kernel/dma/direct.c

+11 −13

Original line number	Diff line number	Diff line
		@@ -472,28 +472,26 @@ int dma_direct_mmap(struct device dev, struct vm_area_struct vma,
		}
		#endif /* CONFIG_MMU */

		/*
		* Because 32-bit DMA masks are so common we expect every architecture to be
		* able to satisfy them - either by not supporting more physical memory, or by
		* providing a ZONE_DMA32. If neither is the case, the architecture needs to
		* use an IOMMU instead of the direct mapping.
		*/
		int dma_direct_supported(struct device *dev, u64 mask)
		{
		u64 min_mask;

		if (IS_ENABLED(CONFIG_ZONE_DMA))
		min_mask = DMA_BIT_MASK(zone_dma_bits);
		else
		min_mask = DMA_BIT_MASK(32);
		u64 min_mask = (max_pfn - 1) << PAGE_SHIFT;

		min_mask = min_t(u64, min_mask, (max_pfn - 1) << PAGE_SHIFT);
		/*
		* Because 32-bit DMA masks are so common we expect every architecture
		* to be able to satisfy them - either by not supporting more physical
		* memory, or by providing a ZONE_DMA32. If neither is the case, the
		* architecture needs to use an IOMMU instead of the direct mapping.
		*/
		if (mask >= DMA_BIT_MASK(32))
		return 1;

		/*
		* This check needs to be against the actual bit mask value, so
		* use __phys_to_dma() here so that the SME encryption mask isn't
		* part of the check.
		*/
		if (IS_ENABLED(CONFIG_ZONE_DMA))
		min_mask = min_t(u64, min_mask, DMA_BIT_MASK(zone_dma_bits));
		return mask >= __phys_to_dma(dev, min_mask);
		}

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