Re: [PATCH v6 00/20] dma-mapping: Use DMA_ATTR_CC_SHARED through direct, pool and swiotlb paths

[Aneesh Kumar K.V <aneesh.kumar@kernel.org>]

Catalin Marinas <catalin.marinas@arm.com> writes:

> On Thu, Jun 04, 2026 at 02:09:39PM +0530, Aneesh Kumar K.V (Arm) wrote:
>> This series propagates DMA_ATTR_CC_SHARED through the dma-direct,
>> dma-pool, and swiotlb paths so that encrypted and decrypted DMA buffers
>> are handled consistently.
>> 
>> Today, the direct DMA path mostly relies on force_dma_unencrypted() for
>> shared/decrypted buffer handling. This series consolidates the
>> force_dma_unencrypted() checks in the top-level functions and ensures
>> that the remaining DMA interfaces use DMA attributes to make the correct
>> decisions.
>
> Please check Sashiko's reports, it has some good points:
>
> https://sashiko.dev/#/patchset/20260604083959.1265923-1-aneesh.kumar@kernel.org
>
> I think the main one is the swiotlb_tbl_map_single() changes which break
> AMD SME host support. There cc_platform_has(CC_ATTR_MEM_ENCRYPT) is true
> but force_dma_unencrypted() is false. Normally you'd not end up on this
> path but you can have swiotlb=force.
>

I would consider the above similar to a trusted device requiring swiotlb
bouncing. At some point, based on real-world use cases, we may need to
add protected io_tlb_mem pools. We have not done that yet because no
such use case has come so far.

-aneesh