linux-kernel - Re: [PATCH v12 3/9] tee: implement protected DMA-heap

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Message-ID: <CAHUa44H3nGgY9q68YRRp5A7Q6Ku3P_URuv+L7H8chYzLAKd8mQ@mail.gmail.com>
Date: Thu, 2 Oct 2025 14:57:25 +0200
From: Jens Wiklander <jens.wiklander@...aro.org>
To: Maxime Ripard <mripard@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-media@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org, 
	op-tee@...ts.trustedfirmware.org, linux-arm-kernel@...ts.infradead.org, 
	Olivier Masse <olivier.masse@....com>, Thierry Reding <thierry.reding@...il.com>, 
	Yong Wu <yong.wu@...iatek.com>, Sumit Semwal <sumit.semwal@...aro.org>, 
	Benjamin Gaignard <benjamin.gaignard@...labora.com>, Brian Starkey <Brian.Starkey@....com>, 
	John Stultz <jstultz@...gle.com>, "T . J . Mercier" <tjmercier@...gle.com>, 
	Christian König <christian.koenig@....com>, 
	Sumit Garg <sumit.garg@...nel.org>, Matthias Brugger <matthias.bgg@...il.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, azarrabi@....qualcomm.com, 
	Simona Vetter <simona.vetter@...ll.ch>, Daniel Stone <daniel@...ishbar.org>, 
	Rouven Czerwinski <rouven.czerwinski@...aro.org>, robin.murphy@....com, 
	Sumit Garg <sumit.garg@....qualcomm.com>
Subject: Re: [PATCH v12 3/9] tee: implement protected DMA-heap

Hi,

On Thu, Oct 2, 2025 at 9:54 AM Maxime Ripard <mripard@...hat.com> wrote:
>
> On Thu, Sep 11, 2025 at 03:49:44PM +0200, Jens Wiklander wrote:
> > +static const char *heap_id_2_name(enum tee_dma_heap_id id)
> > +{
> > +     switch (id) {
> > +     case TEE_DMA_HEAP_SECURE_VIDEO_PLAY:
> > +             return "protected,secure-video";
> > +     case TEE_DMA_HEAP_TRUSTED_UI:
> > +             return "protected,trusted-ui";
> > +     case TEE_DMA_HEAP_SECURE_VIDEO_RECORD:
> > +             return "protected,secure-video-record";
> > +     default:
> > +             return NULL;
> > +     }
> > +}
>
> We've recently agreed on a naming guideline (even though it's not merged yet)
>
> https://lore.kernel.org/r/20250728-dma-buf-heap-names-doc-v4-1-f73f71cf0dfd@kernel.org

I wasn't aware of that (or had forgotten it), but during the revisions
of this patch set, we changed to use "protected".

>
> Secure and trusted should be defined I guess, because secure and
> protected at least seem redundant to me.

Depending on the use case, the protected buffer is only accessible to
a specific set of devices. This is typically configured by the TEE
firmware based on which heap we're using. To distinguish between the
different heaps, I've simply added the name of the use case after the
comma. So the name of the heap for the Trusted-UI use case is
"protected,trusted-ui". What would a heap called "protected,ui"
represent? Protected buffers for a UI use case? What kind of UI use
case? If the name of the heap is too generic, it might cover more than
one use case with conflicting requirements for which devices should be
able to access the protected memory.

Thanks,
Jens