Re: [PATCH V8 06/44] mm/pkeys: Add Kconfig options for PKS

Dave Hansen
2022-01-28T22:54:35Z

On 1/27/22 09:54, ira.weiny@intel.com wrote:
> From: Ira Weiny <ira.weiny@intel.com>
>
> Protection Key Supervisor, PKS, is a feature used by kernel code only.
> As such if no kernel users are configured the PKS code is unnecessary
> overhead.
>
> Define a Kconfig structure which allows kernel code to detect PKS
> support by an architecture and then subsequently enable that support
> within the architecture.
>
> ARCH_HAS_SUPERVISOR_PKEYS indicates to kernel consumers that an
> architecture supports pkeys. PKS users can then select
> ARCH_ENABLE_SUPERVISOR_PKEYS to turn on the support within the
> architecture.
>
> If ARCH_ENABLE_SUPERVISOR_PKEYS is not selected architectures avoid the
> PKS overhead.
>
> ARCH_ENABLE_SUPERVISOR_PKEYS remains off until the first kernel use case
> sets it.

This is heavy on the "what" and weak on the "why".

Why isn't this an x86-specific Kconfig? Why do we need two Kconfigs?
Good old user pkeys only has one:

config ARCH_HAS_PKEYS
bool

and it's in arch-generic code because there are ppc and x86
implementations *and* the pkey support touches generic code.

This might become evident later in the series, but it's clear as mud as
it stands.