linux-kernel - Re: [PATCH v6 0/5] x86/cpufeatures: Automatically generate required and disabled feature masks

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Message-ID: <Z8GBS81JWP7dl5s2@gmail.com>
Date: Fri, 28 Feb 2025 10:26:35 +0100
From: Ingo Molnar <mingo@...nel.org>
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, bp@...en8.de,
	dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
	will@...nel.org, peterz@...radead.org, yury.norov@...il.com,
	akpm@...ux-foundation.org, acme@...nel.org, namhyung@...nel.org,
	brgerst@...il.com, andrew.cooper3@...rix.com, nik.borisov@...e.com
Subject: Re: [PATCH v6 0/5] x86/cpufeatures: Automatically generate required
 and disabled feature masks


* Xin Li (Intel) <xin@...or.com> wrote:

> The x86 build process first generates required and disabled feature
> masks based on current build config, and then uses these generated
> masks to compile the source code.  When a CPU feature is not enabled
> in a build config, e.g., when CONFIG_X86_FRED=n, its feature disable
> flag, i.e., DISABLE_FRED, needs to be properly defined and added to
> a specific disabled CPU features mask in <asm/disabled-features.h>,
> as the following patch does:
> https://lore.kernel.org/all/20231205105030.8698-8-xin3.li@intel.com/.
> As a result, the FRED feature bit is surely cleared in the generated
> kernel binary when CONFIG_X86_FRED=n.
> 
> Recently there is another case to repeat the same exercise for the
> AMD SEV-SNP CPU feature:
> https://lore.kernel.org/all/20240126041126.1927228-2-michael.roth@amd.com/.
> https://lore.kernel.org/all/20240126041126.1927228-23-michael.roth@amd.com/.
> 
> It was one thing when there were four of CPU feature masks, but with
> over 20 it is going to cause mistakes, e.g.,
> https://lore.kernel.org/lkml/aaed79d5-d683-d1bc-7ba1-b33c8d6db618@suse.com/.
> 
> We want to eliminate the stupidly repeated exercise to manually assign
> features to CPU feature words through introducing an AWK script to
> automatically generate a header with required and disabled CPU feature
> masks based on current build config, and this patch set does that.
> 
> Link to v5:
> https://lore.kernel.org/lkml/20250106070727.3211006-1-xin@zytor.com/
> 
> 
> H. Peter Anvin (Intel) (3):
>   x86/cpufeatures: Rename X86_CMPXCHG64 to X86_CX8
>   x86/cpufeatures: Add {required,disabled} feature configs
>   x86/cpufeatures: Generate a feature mask header based on build config
> 
> Xin Li (Intel) (2):
>   x86/cpufeatures: Remove {disabled,required}-features.h
>   x86/cpufeatures: Use AWK to generate {REQUIRED|DISABLED}_MASK_BIT_SET

>  24 files changed, 320 insertions(+), 634 deletions(-)

Very nice!

Reviewed-by: Ingo Molnar <mingo@...nel.org>

Thanks,

	Ingo