Re: [PATCH v8 00/23] dma-mapping: Track shared DMA state through direct, pool and swiotlb paths

[Marek Szyprowski]

On 25.07.2026 09:09, Aneesh Kumar K.V wrote:
> "Aneesh Kumar K.V (Arm)" <aneesh.kumar@xxxxxxxxxx> writes:
>> This series tracks confidential-computing shared DMA state 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.
>>
>> The series separates mapping and allocation state:
>> - DMA_ATTR_CC_SHARED describes the DMA address attribute requested for a
>>   mapping. It tells the DMA mapping path that the DMA address must target
>>   shared/decrypted memory.
>> - __DMA_ATTR_ALLOC_CC_SHARED is an internal DMA-mapping attribute used only
>>   by allocation paths after the DMA core decides that the backing pages
>>   must be allocated as shared/decrypted memory.
>>
>> The series:
>> - moves swiotlb-backed allocations out of __dma_direct_alloc_pages(),
>> - uses __DMA_ATTR_ALLOC_CC_SHARED through the dma-direct alloc/free paths
>> - teaches the atomic DMA pools to track encrypted versus decrypted
>>   state
>> - tracks swiotlb pool encryption state and enforces strict pool
>>   selection
>> - centralizes encrypted/decrypted pgprot handling in dma_pgprot() using
>>   DMA attributes
>> - passes DMA attributes down to dma_capable() so capability checks can
>>   validate whether the selected DMA address encoding matches
>>   DMA_ATTR_CC_SHARED
>> - makes dma_direct_map_phys() choose the DMA address encoding from
>>   DMA_ATTR_CC_SHARED and fall back to swiotlb when a shared DMA request
>>   cannot use the direct mapping, which lets arm64 and x86 CCA guests stop
>>   relying on SWIOTLB_FORCE for DMA mappings
>> - use the selected swiotlb pool state to derive the returned DMA
>>   address
>> - reports CC_ATTR_GUEST_MEM_ENCRYPT for arm64 Realms, powerpc secure
>>   guests, and s390 protected virtualization guests.
>>
>> Dependency:
>> This series depends on the pKVM changes posted at:
>> https://lore.kernel.org/all/20260603110522.3331819-1-smostafa@xxxxxxxxxx
>>
>> Please merge this series only after the pKVM changes above are merged.
>> Otherwise pKVM will be broken.
>>
> pKVM topic branch is now available 
>
> https://lore.kernel.org/all/178467286876.125042.12010461715645610054.b4-ty@xxxxxxxxxx/
>
> https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-next/coco
I've just got back from my holiday's and I see that there is everything ready to give
this patchset some tests in linux-next. I hope nothing will break.

I've applied this patchset to dma-mapping-for-next, on top of pKVM topic branch with
patch "[PATCH v8 17/23] dma-direct: make dma_direct_map_phys() honor DMA_ATTR_CC_SHARED"
rebased onto latest changes in arch/arm64/mm/init.c.

The remaining items pointed in the review can be fixed incrementally.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland