Re: [PATCH v7 00/22] dma-mapping: Track shared DMA state through direct, pool and swiotlb paths

[Marek Szyprowski <m.szyprowski@samsung.com>]

On 07.07.2026 10:06, Aneesh Kumar K.V wrote:
> "Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel.org> 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@google.com
>>
>> Please merge this series only after the pKVM changes above are merged.
>> Otherwise pKVM will be broken.
>>
> A rebased tree on top of the dependent pKVM changes can be found at:
> https://gitlab.arm.com/linux-arm/linux-cca/-/tree/scratch/pkvm/testing?ref_type=heads
>
> The patches had minor conflicts. I am not sure how we want to get this
> merged.
>
> Should we ask the pKVM maintainers for a topic branch, and then I can
> repost the updated series on top of that?
I'm fine with merging on top of the topic branch and I assume that this
patchset is mature enough to give it a try in linux-next, but first I
would like to get a review or at least acks from others with good CC
knowledge or experience.

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