Re: [RFC PATCH v2 1/3] arm64: add CPU prefetch and cache modulation sysfs interface

[Will Deacon <will@kernel.org>]

On Thu, Oct 15, 2026 at 08:29:06PM +0800, Koba Ko wrote:
> Thanks for explaining the rebase, rollout and debugging costs of carrying
> this out of tree. That's useful context from someone using the patchset.
> 
> CONFIG_EXPERT plus tainting on use could make experimental use more
> explicit. Those safeguards alone would not establish that firmware
> access, virtualization and runtime register updates are handled safely;
> the local restrictions still need validation against the hardware and
> firmware requirements.
> 
> I'd like to hear Will's view on whether this opt-in approach could be
> acceptable in principle, and what requirements it would need to meet.
> I'm not planning to submit v3.

No, this isn't something we should be maintaining in the upstream kernel
and if we take this then we'll suddenly grow a zoo full of this stuff.

If Nvidia has imp-def controls that they believe are useful to expose to
userspace, then I suggest working with Arm to get something architectural
that we can support across different pieces of hardware and which would
integrate properly with the rest of the architecture (including things
like virtualisation and debug).

Will