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

Sumit Semwal
2026-04-02T04:41:45Z

Hello Jiri,

On Thu, 26 Mar 2026 at 00:53, Jiri Pirko <jiri@resnulli.us> 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.

Thank you for the patch series, it looks good to me.

Marek, if you are ok, please could you take it through your tree, with my
Acked-by: Sumit Semwal <sumit.semwal@linaro.org>

Best,
Sumit.
>
> Based on dma-mapping-for-next e7442a68cd1ee797b585f045d348781e9c0dde0d
>
> Jiri Pirko (2):
> dma-mapping: introduce DMA_ATTR_CC_SHARED for shared memory
> dma-buf: heaps: system: add system_cc_shared heap for explicitly
> shared memory
>
> drivers/dma-buf/heaps/system_heap.c | 103 ++++++++++++++++++++++++++--
> include/linux/dma-mapping.h | 10 +++
> include/trace/events/dma.h | 3 +-
> kernel/dma/direct.h | 14 +++-
> kernel/dma/mapping.c | 13 +++-
> 5 files changed, 132 insertions(+), 11 deletions(-)
>
> --
> 2.51.1
>