Re: [PATCH 05/11] ARM: dma-mapping: Bypass the legacy path for core-owned DMA API domains

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] arm: loss of per-device IOVA bounds for core-owned domains in ARM32 IOMMU DMA
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commit ebe6429aeb25c05897865b7deefe9f71d234666a
Author: Mikko Perttunen <mperttunen@nvidia.com>

ARM: dma-mapping: Bypass the legacy path for core-owned DMA API domains

This commit updates the ARM DMA mapping logic to bypass custom IOMMU domain
management when a core-owned DMA default domain is requested. It adds checks
in arm_setup_iommu_dma_ops() and arm_teardown_iommu_dma_ops() to skip legacy
initialization and teardown steps if an existing cookie indicates core
ownership.

> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index e0d58778c5f54..91f12fb91509e 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -1761,9 +1761,18 @@ EXPORT_SYMBOL_GPL(arm_iommu_detach_device);
>  
>  static void arm_setup_iommu_dma_ops(struct device *dev)
>  {
> -	struct dma_iommu_mapping *mapping;
> +	struct dma_iommu_mapping *mapping = to_dma_iommu_mapping(dev);
>  	u64 dma_base = 0, size = 1ULL << 32;
>  
> +	/*
> +	 * An existing cookie means the core owns the domain. Only set the
> +	 * per-binding DMA ops.
> +	 */
> +	if (mapping) {
> +		set_dma_ops(dev, &iommu_ops);
> +		return;
> +	}
> +
>  	if (dev->dma_range_map) {

[Severity: High]
Does this early return cause core-owned domains to bypass the legacy logic
that extracts and applies per-device dma_range_map constraints to the IOVA
space?

If a device specifies a dma-ranges property in DT and operates under an
IOMMU driver that opts into the IOMMU_DOMAIN_DMA default domain, it seems
this early return bypasses the custom mapping initialization that previously
baked the dma_range_map constraints into mapping->base and mapping->size.

When iommu_ops.alloc is called, won't the ARM32 legacy allocator
__alloc_iova() assign IOVAs based solely on the generic IOMMU aperture
geometry, ignoring these device-specific constraints?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260915-b4-arm32-iommu-dma-cookie-v1-0-ba4f9d33a2b8@nvidia.com?part=5