Re: [PATCH v5 0/2] dma-buf: heaps: system: add an option to allocate explicitly shared/decrypted memory

Jason Gunthorpe
2026-03-27T12:10:24Z

On Fri, Mar 27, 2026 at 10:38:10AM +0100, Marek Szyprowski wrote:
> On 25.03.2026 20:23, Jiri Pirko wrote:
> > From: Jiri Pirko <jiri@nvidia.com>
> >
> > Confidential computing (CoCo) VMs/guests, such as AMD SEV and Intel TDX,
> > run with private/encrypted memory which creates a challenge
> > for devices that do not support DMA to it (no TDISP support).
> >
> > For kernel-only DMA operations, swiotlb bounce buffering provides a
> > transparent solution by copying data through shared memory.
> > However, the only way to get this memory into userspace is via the DMA
> > API's dma_alloc_pages()/dma_mmap_pages() type interfaces which limits
> > the use of the memory to a single DMA device, and is incompatible with
> > pin_user_pages().
> >
> > These limitations are particularly problematic for the RDMA subsystem
> > which makes heavy use of pin_user_pages() and expects flexible memory
> > usage between many different DMA devices.
> >
> > This patch series enables userspace to explicitly request shared
> > (decrypted) memory allocations from new dma-buf system_cc_shared heap.
> > Userspace can mmap this memory and pass the dma-buf fd to other
> > existing importers such as RDMA or DRM devices to access the
> > memory. The DMA API is improved to allow the dma heap exporter to DMA
> > map the shared memory to each importing device.
> >
> > Based on dma-mapping-for-next e7442a68cd1ee797b585f045d348781e9c0dde0d
>
> I would like to merge this to dma-mapping-next, but I feel a bit
> uncomfortable with my lack of knowledge about CoCo and friends. Could
> those who know a bit more about it provide some Reviewed-by tags?

I'm confident in the CC stuff, I was hoping to see someone from dmabuf
heap land ack that the uAPI design is OK.. TJ?

Jason