[RFC PATCH 0/4] uapi, drm: Add and implement RLIMIT_GPUPRIO

[Joshua Ashton]

Hello all!

I would like to propose a new API for allowing processes to control
the priority of GPU queues similar to RLIMIT_NICE/RLIMIT_RTPRIO.

The main reason for this is for compositors such as Gamescope and
SteamVR vrcompositor to be able to create realtime async compute
queues on AMD without the need of CAP_SYS_NICE.

The current situation is bad for a few reasons, one being that in order
to setcap the executable, typically one must run as root which involves
a pretty high privelage escalation in order to achieve one
small feat, a realtime async compute queue queue for VR or a compositor.
The executable cannot be setcap'ed inside a
container nor can the setcap'ed executable be run in a container with
NO_NEW_PRIVS.

I go into more detail in the description in
`uapi: Add RLIMIT_GPUPRIO`.

My initial proposal here is to add a new RLIMIT, `RLIMIT_GPUPRIO`,
which seems to make most initial sense to me to solve the problem.

I am definitely not set that this is the best formulation however
or if this should be linked to DRM (in terms of it's scheduler
priority enum/definitions) in any way and and would really like other
people's opinions across the stack on this.

Once initial concern is that potentially this RLIMIT could out-live
the lifespan of DRM. It sounds crazy saying it right now, something
that definitely popped into my mind when touching `resource.h`. :-)

Anyway, please let me know what you think!
Definitely open to any feedback and advice you may have. :D

Thanks!
 - Joshie

Joshua Ashton (4):
  drm/scheduler: Add DRM_SCHED_PRIORITY_VERY_HIGH
  drm/scheduler: Split out drm_sched_priority to own file
  uapi: Add RLIMIT_GPUPRIO
  drm/amd/amdgpu: Check RLIMIT_GPUPRIO in priority permissions

 drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c | 13 ++++++--
 drivers/gpu/drm/msm/msm_gpu.h           |  2 +-
 fs/proc/base.c                          |  1 +
 include/asm-generic/resource.h          |  3 +-
 include/drm/drm_sched_priority.h        | 41 +++++++++++++++++++++++++
 include/drm/gpu_scheduler.h             | 14 +--------
 include/uapi/asm-generic/resource.h     |  3 +-
 7 files changed, 58 insertions(+), 19 deletions(-)
 create mode 100644 include/drm/drm_sched_priority.h

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2.40.0