linux-kernel - Re: [RESEND v1 1/3] x86/cpufeatures: Add {required,disabled} feature configs

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Date: Wed, 12 Jun 2024 15:33:40 +0200
From: Borislav Petkov <bp@...en8.de>
To: "Xin Li (Intel)" <xin@...or.com>
Cc: linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
	tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
	x86@...nel.org, hpa@...or.com, will@...nel.org,
	peterz@...radead.org, akpm@...ux-foundation.org, acme@...nel.org,
	namhyung@...nel.org
Subject: Re: [RESEND v1 1/3] x86/cpufeatures: Add {required,disabled} feature
 configs

On Thu, May 09, 2024 at 01:53:38PM -0700, Xin Li (Intel) wrote:
> diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu
> index 2a7279d80460..719302d37053 100644
> --- a/arch/x86/Kconfig.cpu
> +++ b/arch/x86/Kconfig.cpu
> @@ -358,6 +358,10 @@ config X86_P6_NOP
>  	depends on X86_64
>  	depends on (MCORE2 || MPENTIUM4 || MPSC)
>  
> +config X86_REQUIRED_FEATURE_NOPL

Can we keep the X86_{REQUIRED,DISABLED}_ prefixes solely in
arch/x86/Kconfig.cpufeatures and not spill them out into the rest of the tree?

This way there will be no confusion between X86_FEATURE_, X86_REQUIRED_FEATURE_,
X86_DISABLED_FEATURE_ and so on, and which one I am supposed to use where...

> diff --git a/arch/x86/Kconfig.cpufeatures b/arch/x86/Kconfig.cpufeatures
> new file mode 100644
> index 000000000000..326a8410ff06
> --- /dev/null
> +++ b/arch/x86/Kconfig.cpufeatures
> @@ -0,0 +1,153 @@
> +# SPDX-License-Identifier: GPL-2.0
> +#
> +# x86 feature bits (see arch/x86/include/asm/cpufeatures.h) that are
> +# either REQUIRED to be enabled, or DISABLED (always ignored) for this
> +# particular compile-time configuration.  The tests for these features
> +# are turned into compile-time constants via the generated
> +# <asm/featuremasks.h>.
> +#
> +# The naming of these variables *must* match asm/cpufeatures.h.

I presume they must match X86_FEATURE_<name>?

And REQUIRED and DISABLED is manipulated in by the script?

I guess I'll see later.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette