linux-kernel - Re: [PATCH v5 1/5] x86/cpufeatures: Add {required,disabled} feature configs

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Message-ID: <20250215142017.GCZ7CioRHgpm6a-eIZ@fat_crate.local>
Date: Sat, 15 Feb 2025 15:20:17 +0100
From: Borislav Petkov <bp@...en8.de>
To: "H. Peter Anvin" <hpa@...or.com>
Cc: "Xin Li (Intel)" <xin@...or.com>, 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,
	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 v5 1/5] x86/cpufeatures: Add {required,disabled} feature
 configs

On Sat, Feb 15, 2025 at 02:12:35AM -0800, H. Peter Anvin wrote:
> CX8 is the name of the CPUID flag, for better or worse. 

Right, so a separate patch:

git grep X86_CMPXCHG64
arch/x86/Kconfig:135:   select ARCH_USE_CMPXCHG_LOCKREF         if X86_CMPXCHG64
arch/x86/Kconfig.cpu:369:config X86_CMPXCHG64
arch/x86/Kconfig.cpu:383:       default "5" if X86_32 && X86_CMPXCHG64
arch/x86/include/asm/asm-prototypes.h:19:#ifndef CONFIG_X86_CMPXCHG64
arch/x86/include/asm/atomic64_32.h:51:#ifdef CONFIG_X86_CMPXCHG64
arch/x86/include/asm/cmpxchg_32.h:72:#ifdef CONFIG_X86_CMPXCHG64
arch/x86/include/asm/required-features.h:26:#ifdef CONFIG_X86_CMPXCHG64
arch/x86/lib/Makefile:59:ifneq ($(CONFIG_X86_CMPXCHG64),y)
arch/x86/lib/cmpxchg8b_emu.S:10:#ifndef CONFIG_X86_CMPXCHG64
lib/atomic64_test.c:257:#elif defined(CONFIG_X86_CMPXCHG64)
tools/arch/x86/include/asm/required-features.h:26:#ifdef CONFIG_X86_CMPXCHG64

should be easy.

> It seems to me to be a bit silly to have dummy symbols that mean literally
> the same thing, but ...

Why if they're confined and encapsulated in a single file:
arch/x86/Kconfig.cpufeatures ?

Rest of the kernel doesn't need to know whether a feature is required or not,
right?

-- 
Regards/Gruss,
    Boris.

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