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

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Message-ID: <9d0e381758c0e83882b57102fb09c5d3a36fbf57.camel@ndufresne.ca>
Date: Thu, 30 Jan 2025 12:47:02 -0500
From: Nicolas Dufresne <nicolas@...fresne.ca>
To: Maxime Ripard <mripard@...nel.org>
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

Le jeudi 30 janvier 2025 à 17:38 +0100, Maxime Ripard a écrit :
> 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.

I get that using memory region is somewhat more of an HW description, and
aligned with what a DT is supposed to describe. One of the challenge is that
Mediatek heap proposal endup calling into their TEE, meaning knowing the region
is not that useful. You actually need the TEE APP guid and its IPC protocol. If
we can dell drivers to use a head instead, we can abstract that SoC specific
complexity. I believe each allocated addressed has to be mapped to a zone, and
that can only be done in the secure application. I can imagine similar needs
when the protection is done using some sort of a VM / hypervisor.

Nicolas

> 
> > 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