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

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Message-ID: <CAHUa44EGWuVPjoxpG-S66he=6dkvkwzxNewaGKVKXUxrO41ztg@mail.gmail.com>
Date: Tue, 8 Apr 2025 15:28:45 +0200
From: Jens Wiklander <jens.wiklander@...aro.org>
To: Sumit Garg <sumit.garg@...nel.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 8, 2025 at 11:14 AM Sumit Garg <sumit.garg@...nel.org> wrote:
>
> 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.

I hope, without too much difficulty. They are after all looking for a
way to allocate memory from a DMA heap.

> So it's better we provide a generic kernel
> Kconfig which enables all the default features.

I disagree, it should be possible to configure without DMABUF_HEAPS if desired.

>
> > 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.

I was saving that for a later patch set as a later problem. We may
save some time by not doing it now.

Cheers,
Jens

>
> -Sumit
>
> >
> > Cheers,
> > Jens