Re: [PATCH v7 09/22] dma-mapping: Add internal shared allocation attribute

[Jason Gunthorpe]

On Wed, Jul 01, 2026 at 11:19:13AM +0530, Aneesh Kumar K.V (Arm) wrote:
> DMA_ATTR_CC_SHARED describes an existing DMA mapping whose backing memory
> is already shared, or decrypted, for confidential computing. It is a
> mapping attribute: callers use it to request a shared DMA address encoding
> for memory that has already been prepared for shared DMA.
> 
> Allocation paths need a related but different state. Once the DMA core
> decides that an allocation must use shared backing pages, the lower-level
> allocation helpers need to select shared pools, decrypt newly allocated
> pages, derive the DMA address with the shared-memory translation and
> restore encryption on free. That state is internal to the DMA-mapping
> implementation and should not be passed by drivers to dma_alloc_attrs().
> 
> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@xxxxxxxxxx>
> ---
>  Documentation/core-api/dma-attributes.rst | 29 +++++++++++++++++++++++
>  include/linux/dma-mapping.h               |  8 +++++++
>  include/trace/events/dma.h                |  3 ++-
>  3 files changed, 39 insertions(+), 1 deletion(-)

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Jason