linux-kernel - Re: [RFC PATCH 0/5] drm/panthor: Protected mode support for Mali CSF GPUs

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Message-ID: <ppznh3xnfuqrozhrc7juyi3enxc4v3meu4wadkwwzecj7oxex7@moln2fiibbxo>
Date: Thu, 30 Jan 2025 17:38:29 +0100
From: Maxime Ripard <mripard@...nel.org>
To: Nicolas Dufresne <nicolas@...fresne.ca>
Cc: Florent Tomasin <florent.tomasin@....com>, 
	Vinod Koul <vkoul@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Boris Brezillon <boris.brezillon@...labora.com>, Steven Price <steven.price@....com>, 
	Liviu Dudau <liviu.dudau@....com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, 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>, Yong Wu <yong.wu@...iatek.com>, dmaengine@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	linux-media@...r.kernel.org, linaro-mm-sig@...ts.linaro.org, 
	linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org, nd@....com, 
	Akash Goel <akash.goel@....com>
Subject: Re: [RFC PATCH 0/5] drm/panthor: Protected mode support for Mali CSF
 GPUs

Hi Nicolas,

On Thu, Jan 30, 2025 at 10:59:56AM -0500, Nicolas Dufresne wrote:
> Le jeudi 30 janvier 2025 à 14:46 +0100, Maxime Ripard a écrit :
> > Hi,
> > 
> > I started to review it, but it's probably best to discuss it here.
> > 
> > On Thu, Jan 30, 2025 at 01:08:56PM +0000, Florent Tomasin wrote:
> > > Hi,
> > > 
> > > This is a patch series covering the support for protected mode execution in
> > > Mali Panthor CSF kernel driver.
> > > 
> > > The Mali CSF GPUs come with the support for protected mode execution at the
> > > HW level. This feature requires two main changes in the kernel driver:
> > > 
> > > 1) Configure the GPU with a protected buffer. The system must provide a DMA
> > >    heap from which the driver can allocate a protected buffer.
> > >    It can be a carved-out memory or dynamically allocated protected memory region.
> > >    Some system includes a trusted FW which is in charge of the protected memory.
> > >    Since this problem is integration specific, the Mali Panthor CSF kernel
> > >    driver must import the protected memory from a device specific exporter.
> > 
> > Why do you need a heap for it in the first place? My understanding of
> > your series is that you have a carved out memory region somewhere, and
> > you want to allocate from that carved out memory region your buffers.
> > 
> > How is that any different from using a reserved-memory region, adding
> > the reserved-memory property to the GPU device and doing all your
> > allocation through the usual dma_alloc_* API?
> 
> How do you then multiplex this region so it can be shared between
> GPU/Camera/Display/Codec drivers and also userspace ?

You could point all the devices to the same reserved memory region, and
they would all allocate from there, including for their userspace-facing
allocations.

> Also, how the secure memory is allocted / obtained is a process that
> can vary a lot between SoC, so implementation details assumption
> should not be coded in the driver.

But yeah, we agree there, it's also the point I was trying to make :)

Maxime

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