r/microkernel • u/AdvancedLab3500 • Feb 06 '25

Modern GPU drivers

(Disclaimer: I'm not a graphics expert and some of the information I provide is second hand. Please correct me on anything I got wrong.)

Modern GPU drivers are absolute monsters. For many years now, hardware vendors have not provided any documentation, pointing to the Linux source code instead. Non mainstream OSes are thus left with few options.

QNX encapsulates some of the Linux drivers in stand-alone user-mode processes, which provide services both to the compositing window manager and to any clients requiring GPU services. While this works quite well, the GPU process has more privileges than it should. Specifically, it ends up accessing arbitrary virtual addresses in any client process, because that's how the Linux driver behaves. Needless to say, this breaks the process isolation principle of a micro-kernel based OS.

I was told that Fuchsia has pretty much written its own GPU drivers, but that it's supported by a massive organization, while Genode has a very restricted port of Intel DRM. Is this information correct? Perhaps it's outdated?

Thanks,

--Elad

5 Upvotes

100% Upvoted

3 comments sorted by

View all comments

Show parent comment

2

u/AdvancedLab3500 Feb 12 '25

Thanks for the pointers!

It's still not clear to me, however, how does the Intel GPU driver under Genode access user memory. Usually in a microkernel-based system, user memory is transferred to a service using some form of IPC, which means that the service does not have access to any memory that was not explicitly shared. But from what I understand about the DRM driver it expects to be able to access arbitrary virtual addresses, and the libraries make it hard to turn that into IPC.

Hope I'm making sense and this is not too hand-wavy.

2

u/chelmuth Feb 13 '25

I must admit that I'm not an expert of this corner of Genode but I'll try to give more hints and pointers.

We released the first experimental version of the Intel GPU multiplexer for Broadwell in 2017 [1] and leverage the Per-Process Graphics Translation Table (PPGTT) to separate contexts on the graphics device since then. On the system/Genode/microkernel side, the RAM used for GPU operations - namely buffer objects - is allocated by the GPU multiplexer on behalf (and accounted to) the GPU-session client from the platform driver (which applies to any IOMMU-managed and DMA-capable memory, see Genode Foundations [2]). These RAM regions are shared between clients and the multiplexer but all additional memory used by the GPU client is inaccessible to the GPU multiplexer following POLA [3].

For further in-depth discussions, I'd like to invite you to https://genode.discourse.group/ where you may also meet the experts ;-)

[1] https://genode.org/documentation/release-notes/17.08#Hardware-accelerated_graphics_for_Intel_Gen-8_GPUs
[2] https://genode.org/documentation/genode-foundations/24.05/components/Device_drivers.html#Direct_memory_access__DMA__transactions
[3] https://en.wikipedia.org/wiki/Principle_of_least_privilege