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

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

[Jiri Pirko]

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>
---
 Documentation/userspace-api/dma-buf-heaps.rst | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Documentation/userspace-api/dma-buf-heaps.rst b/Documentation/userspace-api/dma-buf-heaps.rst
index 05445c83b79a..591732393e7d 100644
--- a/Documentation/userspace-api/dma-buf-heaps.rst
+++ b/Documentation/userspace-api/dma-buf-heaps.rst
@@ -16,6 +16,14 @@ 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 VMs 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

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

[T.J. Mercier]

On Thu, Apr 2, 2026 at 7:11 AM Jiri Pirko <jiri@resnulli.us> wrote:
>
> 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>
> ---
>  Documentation/userspace-api/dma-buf-heaps.rst | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/Documentation/userspace-api/dma-buf-heaps.rst b/Documentation/userspace-api/dma-buf-heaps.rst
> index 05445c83b79a..591732393e7d 100644
> --- a/Documentation/userspace-api/dma-buf-heaps.rst
> +++ b/Documentation/userspace-api/dma-buf-heaps.rst
> @@ -16,6 +16,14 @@ 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 VMs configurations, this heap is

"non-CoCo VM configurations"

> +   not registered.

Doesn't seem like you need to wrap this line.

with that: Reviewed-by: T.J.Mercier <tjmercier@google.com>

> +
>   - 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

Each paragraph starting with '-' confused me for a second there. Those
aren't part of the diff. :)

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

[Jiri Pirko]

Mon, Apr 06, 2026 at 10:20:33PM +0200, tjmercier@google.com wrote:
>On Thu, Apr 2, 2026 at 7:11 AM Jiri Pirko <jiri@resnulli.us> wrote:
>>
>> 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>
>> ---
>>  Documentation/userspace-api/dma-buf-heaps.rst | 8 ++++++++
>>  1 file changed, 8 insertions(+)
>>
>> diff --git a/Documentation/userspace-api/dma-buf-heaps.rst b/Documentation/userspace-api/dma-buf-heaps.rst
>> index 05445c83b79a..591732393e7d 100644
>> --- a/Documentation/userspace-api/dma-buf-heaps.rst
>> +++ b/Documentation/userspace-api/dma-buf-heaps.rst
>> @@ -16,6 +16,14 @@ 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 VMs configurations, this heap is
>
>"non-CoCo VM configurations"
>
>> +   not registered.
>
>Doesn't seem like you need to wrap this line.
>
>with that: Reviewed-by: T.J.Mercier <tjmercier@google.com>

Okay. Thanks!


>
>> +
>>   - 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
>
>Each paragraph starting with '-' confused me for a second there. Those
>aren't part of the diff. :)