linux-kernel - Re: [PATCH v6 05/10] tee: implement restricted DMA-heap

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Message-ID: <Z_To9V-JOKZ7ChhE@sumit-X1>
Date: Tue, 8 Apr 2025 14:44:29 +0530
From: Sumit Garg <sumit.garg@...nel.org>
To: Jens Wiklander <jens.wiklander@...aro.org>
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>,
	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>
Subject: Re: [PATCH v6 05/10] tee: implement restricted DMA-heap

On Tue, Apr 01, 2025 at 10:33:04AM +0200, Jens Wiklander wrote:
> On Tue, Apr 1, 2025 at 9:58 AM Sumit Garg <sumit.garg@...nel.org> wrote:
> >
> > On Tue, Mar 25, 2025 at 11:55:46AM +0100, Jens Wiklander wrote:
> > > Hi Sumit,
> > >
> >
> > <snip>
> >
> > >
> > > >
> > > > > +
> > > > > +#include "tee_private.h"
> > > > > +
> > > > > +struct tee_dma_heap {
> > > > > +     struct dma_heap *heap;
> > > > > +     enum tee_dma_heap_id id;
> > > > > +     struct tee_rstmem_pool *pool;
> > > > > +     struct tee_device *teedev;
> > > > > +     /* Protects pool and teedev above */
> > > > > +     struct mutex mu;
> > > > > +};
> > > > > +
> > > > > +struct tee_heap_buffer {
> > > > > +     struct tee_rstmem_pool *pool;
> > > > > +     struct tee_device *teedev;
> > > > > +     size_t size;
> > > > > +     size_t offs;
> > > > > +     struct sg_table table;
> > > > > +};
> > > > > +
> > > > > +struct tee_heap_attachment {
> > > > > +     struct sg_table table;
> > > > > +     struct device *dev;
> > > > > +};
> > > > > +
> > > > > +struct tee_rstmem_static_pool {
> > > > > +     struct tee_rstmem_pool pool;
> > > > > +     struct gen_pool *gen_pool;
> > > > > +     phys_addr_t pa_base;
> > > > > +};
> > > > > +
> > > > > +#if !IS_MODULE(CONFIG_TEE) && IS_ENABLED(CONFIG_DMABUF_HEAPS)
> > > >
> > > > Can this dependency rather be better managed via Kconfig?
> > >
> > > This was the easiest yet somewhat flexible solution I could find. If
> > > you have something better, let's use that instead.
> > >
> >
> > --- a/drivers/tee/optee/Kconfig
> > +++ b/drivers/tee/optee/Kconfig
> > @@ -5,6 +5,7 @@ config OPTEE
> >         depends on HAVE_ARM_SMCCC
> >         depends on MMU
> >         depends on RPMB || !RPMB
> > +       select DMABUF_HEAPS
> >         help
> >           This implements the OP-TEE Trusted Execution Environment (TEE)
> >           driver.
> 
> I wanted to avoid that since there are plenty of use cases where
> DMABUF_HEAPS aren't needed.

Yeah, but how the users will figure out the dependency to enable DMA
heaps with TEE subsystem. So it's better we provide a generic kernel
Kconfig which enables all the default features.

> This seems to do the job:
> +config TEE_DMABUF_HEAP
> + bool
> + depends on TEE = y && DMABUF_HEAPS
> 
> We can only use DMABUF_HEAPS if the TEE subsystem is compiled into the kernel.

Ah, I see. So we aren't exporting the DMA heaps APIs for TEE subsystem
to use. We should do that such that there isn't a hard dependency to
compile them into the kernel. 

-Sumit

> 
> Cheers,
> Jens