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

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

"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?

-aneesh