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

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Date:   Mon, 14 Feb 2022 11:20:20 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Ira Weiny <ira.weiny@...el.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V8 06/44] mm/pkeys: Add Kconfig options for PKS

On 2/8/22 21:34, Ira Weiny wrote:
>>> In other words, there are two things that must happen before the code
>>> gets compiled in:
>>>
>>> 1. Arch support
>>> 2. One or more features to use the arch support
>> Yes.  I really think we are both say the same thing with different words.
> Is the following more clear?
> 
> <commit>
> 
> PKS is only useful to kernel consumers and is only available on some
> architectures.  If no kernel consumers are configured or PKS support is
> not available the PKS code can be eliminated from the compile.
> 
> Define a Kconfig structure which allows kernel consumers to detect
> architecture support (ARCH_HAS_SUPERVISOR_PKEYS) and, if available,
> indicate that PKS should be compiled in (ARCH_ENABLE_SUPERVISOR_PKEYS).
> 
> In this patch ARCH_ENABLE_SUPERVISOR_PKEYS remains off until the first
> kernel consumer sets it.

It's a bit more clear.  I wish it was more clear about the problem.  I
think it would be well-served to add some specifics and clarify the
*problem*.  Maybe something like:

== Problem ==

PKS support is provided by core x86 architecture code.  Its consumers,
however, may be far-flung device drivers like NVDIMM support.  The PKS
core architecture code is dead weight without a consumer.

--- maybe add one example ---

== Solution ==

Avoid even compiling in the core PKS code if there are no consumers.

== Details ==