linux-kernel - Re: [PATCH v7 0/4] x86/cpufeatures: Automatically generate required and disabled feature masks

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Message-ID: <4b44eaec-2c45-4a68-80c5-6a8c0905b1ab@zytor.com>
Date: Fri, 7 Mar 2025 10:28:56 -0800
From: Xin Li <xin@...or.com>
To: linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Cc: 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,
        sraithal@....com, philip.li@...el.com
Subject: Re: [PATCH v7 0/4] x86/cpufeatures: Automatically generate required
 and disabled feature masks

On 3/5/2025 10:47 AM, Xin Li (Intel) 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 v6:
> https://lore.kernel.org/lkml/20250228082338.73859-1-xin@zytor.com/
> 
> Changes in v7:
> * Fix build error with "make distclean; make headers" (Aithal, Srikanth)
> * Collect reviewed-bys.
> 

This version v7 can be cleanly applied on tip/x86/cpu but NOT the latest 
tip/master.

I guess I don't have to rebase on the latest tip/master and resend it?

Thanks!
     Xin

> 
> H. Peter Anvin (Intel) (2):
>    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
> 
>   arch/x86/Kconfig                              |   2 +
>   arch/x86/Kconfig.cpufeatures                  | 197 ++++++++++++++++++
>   arch/x86/Makefile                             |  15 ++
>   arch/x86/boot/cpucheck.c                      |   3 +-
>   arch/x86/boot/cpuflags.c                      |   1 -
>   arch/x86/boot/mkcpustr.c                      |   3 +-
>   arch/x86/include/asm/Kbuild                   |   1 +
>   arch/x86/include/asm/cpufeature.h             |  70 +------
>   arch/x86/include/asm/cpufeatures.h            |   8 -
>   arch/x86/include/asm/disabled-features.h      | 161 --------------
>   arch/x86/include/asm/required-features.h      | 105 ----------
>   arch/x86/kernel/verify_cpu.S                  |   4 +
>   arch/x86/tools/featuremasks.awk               |  88 ++++++++
>   tools/arch/x86/include/asm/cpufeatures.h      |   8 -
>   .../arch/x86/include/asm/disabled-features.h  | 161 --------------
>   .../arch/x86/include/asm/required-features.h  | 105 ----------
>   tools/perf/check-headers.sh                   |   2 -
>   17 files changed, 311 insertions(+), 623 deletions(-)
>   create mode 100644 arch/x86/Kconfig.cpufeatures
>   delete mode 100644 arch/x86/include/asm/disabled-features.h
>   delete mode 100644 arch/x86/include/asm/required-features.h
>   create mode 100755 arch/x86/tools/featuremasks.awk
>   delete mode 100644 tools/arch/x86/include/asm/disabled-features.h
>   delete mode 100644 tools/arch/x86/include/asm/required-features.h
> 
> 
> base-commit: 32dc26a2f55f71907af0874468298c6ab8a8f7f9