linux-kernel - Re: Safety of opening up /dev/dma_heap/* to physically present users (udev uaccess tag) ?

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Message-ID: <d2a512b2-e6b1-4675-b406-478074bbbe95@linaro.org>
Date: Tue, 7 May 2024 16:15:05 +0100
From: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
 Hans de Goede <hdegoede@...hat.com>
Cc: 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>,
 Lennart Poettering <mzxreary@...inter.de>,
 Robert Mader <robert.mader@...labora.com>,
 Sebastien Bacher <sebastien.bacher@...onical.com>,
 Linux Media Mailing List <linux-media@...r.kernel.org>,
 "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
 linaro-mm-sig@...ts.linaro.org,
 Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
 Milan Zamazal <mzamazal@...hat.com>, Maxime Ripard <mripard@...hat.com>,
 Andrey Konovalov <andrey.konovalov.ynk@...il.com>
Subject: Re: Safety of opening up /dev/dma_heap/* to physically present users
 (udev uaccess tag) ?

On 07/05/2024 16:09, Dmitry Baryshkov wrote:
> Ah, I see. Then why do you require the DMA-ble buffer at all? If you are
> providing data to VPU or DRM, then you should be able to get the buffer
> from the data-consuming device.

Because we don't necessarily know what the consuming device is, if any.

Could be VPU, could be Zoom/Hangouts via pipewire, could for argument 
sake be GPU or DSP.

Also if we introduce a dependency on another device to allocate the 
output buffers - say always taking the output buffer from the GPU, then 
we've added another dependency which is more difficult to guarantee 
across different arches.

---
bod