linux-kernel - Re: [PATCH v9 04/12] x86/mm: get INVLPGB count max from CPUID

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Message-ID: <CA+i-1C2NAFTrmZBFfBf8PFaji9YxQm68pV2qc7VbgHWFTji+Xw@mail.gmail.com>
Date: Fri, 7 Feb 2025 16:10:51 +0100
From: Brendan Jackman <jackmanb@...gle.com>
To: Rik van Riel <riel@...riel.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, bp@...en8.de, 
	peterz@...radead.org, dave.hansen@...ux.intel.com, zhengqi.arch@...edance.com, 
	nadav.amit@...il.com, thomas.lendacky@....com, kernel-team@...a.com, 
	linux-mm@...ck.org, akpm@...ux-foundation.org, jannh@...gle.com, 
	mhklinux@...look.com, andrew.cooper3@...rix.com, 
	Manali Shukla <Manali.Shukla@....com>
Subject: Re: [PATCH v9 04/12] x86/mm: get INVLPGB count max from CPUID

On Thu, 6 Feb 2025 at 05:45, Rik van Riel <riel@...riel.com> wrote:
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index 17b6590748c0..f9b832e971c5 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -338,6 +338,7 @@
>  #define X86_FEATURE_CLZERO             (13*32+ 0) /* "clzero" CLZERO instruction */
>  #define X86_FEATURE_IRPERF             (13*32+ 1) /* "irperf" Instructions Retired Count */
>  #define X86_FEATURE_XSAVEERPTR         (13*32+ 2) /* "xsaveerptr" Always save/restore FP error pointers */
> +#define X86_FEATURE_INVLPGB            (13*32+ 3) /* INVLPGB and TLBSYNC instruction supported. */

Why no "invlpgb" here? Seems like having this flag visible in cpuinfo
would be worthwhile.

If there's a reason to hide it maybe add a comment to explain the
reason? Sorry if this is a stupid question - I also can't see an
obvious rationale for why existing flags do or don't get a name at
runtime.