[PATCH v2] dma-buf: heaps: system: document system_cc_shared heap

[Jiri Pirko <jiri@resnulli.us>]

From: Jiri Pirko <jiri@nvidia.com>

Document the system_cc_shared dma-buf heap that was introduced
recently. Describe its purpose, availability conditions and
relation to confidential computing VMs.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: T.J.Mercier <tjmercier@google.com>
---
 Documentation/userspace-api/dma-buf-heaps.rst | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/userspace-api/dma-buf-heaps.rst b/Documentation/userspace-api/dma-buf-heaps.rst
index 05445c83b79a..f56b743cdb36 100644
--- a/Documentation/userspace-api/dma-buf-heaps.rst
+++ b/Documentation/userspace-api/dma-buf-heaps.rst
@@ -16,6 +16,13 @@ following heaps:
 
  - The ``system`` heap allocates virtually contiguous, cacheable, buffers.
 
+ - The ``system_cc_shared`` heap allocates virtually contiguous, cacheable,
+   buffers using shared (decrypted) memory. It is only present on
+   confidential computing (CoCo) VMs where memory encryption is active
+   (e.g., AMD SEV, Intel TDX). The allocated pages have the encryption
+   bit cleared, making them accessible for device DMA without TDISP
+   support. On non-CoCo VM configurations, this heap is not registered.
+
  - The ``default_cma_region`` heap allocates physically contiguous,
    cacheable, buffers. Only present if a CMA region is present. Such a
    region is usually created either through the kernel commandline
-- 
2.51.1