[PATCH v2 0/2] dma-buf: heaps: system: add an option to allocate explicitly decrypted memory

[Jiri Pirko <jiri@resnulli.us>]

From: Jiri Pirko <jiri@nvidia.com>

Confidential computing (CoCo) VMs/guests, such as AMD SEV and Intel TDX,
run with encrypted/protected 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 decrypted 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 decrypted
(shared) memory allocations from the dma-buf system 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.

---
v1->v2:
 patch1:
  - rebased on top of recent dma-mapping-fixes
 patch2:
  - fixed build errors on s390 by including mem_encrypt.h
  - converted system heap flag implementation to a separate heap

Based on dma-mapping-fixes HEAD d5b5e8149af0f5efed58653cbebf1cb3258ce49a

Jiri Pirko (2):
  dma-mapping: introduce DMA_ATTR_CC_DECRYPTED for pre-decrypted memory
  dma-buf: heaps: system: add system_cc_decrypted heap for explicitly
    decrypted memory

 drivers/dma-buf/heaps/system_heap.c | 103 ++++++++++++++++++++++++++--
 include/linux/dma-heap.h            |   1 +
 include/linux/dma-mapping.h         |   6 ++
 include/trace/events/dma.h          |   3 +-
 include/uapi/linux/dma-heap.h       |   3 +-
 kernel/dma/direct.h                 |  14 +++-
 6 files changed, 119 insertions(+), 11 deletions(-)

-- 
2.51.1