Re: [PATCH v2 0/8] dma-mapping: Use DMA_ATTR_CC_SHARED through direct, pool and swiotlb paths

[Mostafa Saleh <smostafa@google.com>]

On Mon, Apr 20, 2026 at 11:44:07AM +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.

I tested this series on protected KVM and did not see regressions.
Tested-by: Mostafa Saleh <smostafa@google.com>

Next, I will:
- Send the pKVM CC patch separately.
- Review this series.

Thanks,
Mostafa

> 
> The series:
> - moves swiotlb-backed allocations out of __dma_direct_alloc_pages(),
> - propagates DMA_ATTR_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,
> - makes dma_direct_map_phys() choose the DMA address encoding from
>   attrs, and
> - uses the selected swiotlb pool state to derive the returned DMA
>   address.
> 
> Changes from v1:
> * rebased to latest kernel (change from DMA_ATTR_CC_DECRYPTED -> DMA_ATTR_CC_SHARED)
> * Update alloc path such that DMA_ATTR_CC_SHARED s not a caller-visible attribute.
> 
> Aneesh Kumar K.V (Arm) (8):
>   dma-direct: swiotlb: handle swiotlb alloc/free outside
>     __dma_direct_alloc_pages
>   dma-direct: use DMA_ATTR_CC_SHARED in alloc/free paths
>   dma-pool: track decrypted atomic pools and select them via attrs
>   dma: swiotlb: track pool encryption state and honor DMA_ATTR_CC_SHARED
>   dma-mapping: make dma_pgprot() honor DMA_ATTR_CC_SHARED
>   dma-direct: make dma_direct_map_phys() honor DMA_ATTR_CC_SHARED
>   dma-direct: set decrypted flag for remapped DMA allocations
>   dma-direct: select DMA address encoding from DMA_ATTR_CC_SHARED
> 
>  drivers/iommu/dma-iommu.c   |   2 +-
>  include/linux/dma-direct.h  |  10 ++
>  include/linux/dma-map-ops.h |   2 +-
>  include/linux/swiotlb.h     |   7 +-
>  kernel/dma/direct.c         | 185 ++++++++++++++++++++++++++++--------
>  kernel/dma/direct.h         |  25 ++---
>  kernel/dma/mapping.c        |  16 +++-
>  kernel/dma/pool.c           | 154 +++++++++++++++++++-----------
>  kernel/dma/swiotlb.c        |  89 +++++++++++++----
>  9 files changed, 355 insertions(+), 135 deletions(-)
> 
> 
> base-commit: c1f49dea2b8f335813d3b348fd39117fb8efb428
> -- 
> 2.43.0
>