On Fri, Jul 17, 2026 at 11:34:27PM +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(). > > Reviewed-by: Jason Gunthorpe <[email protected]> > Signed-off-by: Aneesh Kumar K.V (Arm) <[email protected]>
Reviewed-by: Mostafa Saleh <[email protected]> Thanks, Mostafa > --- > 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(-) > > diff --git a/Documentation/core-api/dma-attributes.rst > b/Documentation/core-api/dma-attributes.rst > index 123c8468d58f..eee743184acd 100644 > --- a/Documentation/core-api/dma-attributes.rst > +++ b/Documentation/core-api/dma-attributes.rst > @@ -179,3 +179,32 @@ interface when building their uAPIs, when possible. > > It must never be used in an in-kernel driver that only works with > kernel memory. > + > +DMA_ATTR_CC_SHARED > +------------------ > + > +This attribute indicates that a DMA mapping is shared, or decrypted, for > +confidential computing guests. For normal system memory, the caller must > +already have marked the memory decrypted with set_memory_decrypted(). CPU > +PTEs for the mapping must use pgprot_decrypted(), and the same shared > +semantic may be passed to a vIOMMU when it sets up the IOPTE. > + > +This attribute describes an existing mapping. It does not allocate shared > +backing pages and must not be passed to dma_alloc_attrs(). For MMIO, use > +this together with DMA_ATTR_MMIO to indicate shared MMIO. Unless > +DMA_ATTR_MMIO is provided, the mapping requires a struct page. > + > +__DMA_ATTR_ALLOC_CC_SHARED > +-------------------------- > + > +This is an internal DMA-mapping attribute for confidential computing guests. > +It is used by allocation paths after the DMA core has determined that the > +backing pages must be shared, or decrypted. For example, the direct DMA and > +SWIOTLB allocation paths use it to select shared DMA pools, decrypt newly > +allocated pages, derive DMA addresses using the shared-memory translation, > and > +restore encryption on free. > + > +__DMA_ATTR_ALLOC_CC_SHARED differs from DMA_ATTR_CC_SHARED in that it is not > +a caller-visible DMA API attribute. DMA_ATTR_CC_SHARED describes an > +already-shared mapping and requires the caller to have prepared normal > +system memory before mapping it. > diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h > index cc0823a99cfd..a3e880649fa4 100644 > --- a/include/linux/dma-mapping.h > +++ b/include/linux/dma-mapping.h > @@ -103,6 +103,14 @@ > */ > #define DMA_ATTR_CC_SHARED (1UL << 13) > > +/* > + * __DMA_ATTR_ALLOC_CC_SHARED: Internal DMA-mapping attribute used by > + * allocation paths that create shared (decrypted) backing pages for > + * confidential computing guests. Drivers must not pass this attribute to > + * dma_alloc_attrs(). > + */ > +#define __DMA_ATTR_ALLOC_CC_SHARED (1UL << 14) > + > /* > * A dma_addr_t can hold any valid DMA or bus address for the platform. It > can > * be given to a device to use as a DMA source or target. It is specific to > a > diff --git a/include/trace/events/dma.h b/include/trace/events/dma.h > index 31c9ddf72c9d..9df02c1511de 100644 > --- a/include/trace/events/dma.h > +++ b/include/trace/events/dma.h > @@ -35,7 +35,8 @@ TRACE_DEFINE_ENUM(DMA_NONE); > { DMA_ATTR_MMIO, "MMIO" }, \ > { DMA_ATTR_DEBUGGING_IGNORE_CACHELINES, "CACHELINES_OVERLAP" }, > \ > { DMA_ATTR_REQUIRE_COHERENT, "REQUIRE_COHERENT" }, \ > - { DMA_ATTR_CC_SHARED, "CC_SHARED" }) > + { DMA_ATTR_CC_SHARED, "CC_SHARED" }, \ > + { __DMA_ATTR_ALLOC_CC_SHARED, "ALLOC_CC_SHARED" }) > > DECLARE_EVENT_CLASS(dma_map, > TP_PROTO(struct device *dev, phys_addr_t phys_addr, dma_addr_t dma_addr, > -- > 2.43.0 >
