linux-kernel - Re: [PATCH] x86/cpufeature: drop *_MASK

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Date:   Tue, 27 Aug 2019 09:41:51 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Cao jin <caoj.fnst@...fujitsu.com>,
        Dave Hansen <dave.hansen@...el.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, tglx@...utronix.de,
        mingo@...hat.com, hpa@...or.com
Subject: Re: [PATCH] x86/cpufeature: drop *_MASK_CEHCK

On Tue, Aug 27, 2019 at 03:05:50PM +0800, Cao jin wrote:
> They are wrappers of BUILD_BUG_ON_ZERO(NCAPINTS != n), which is already
> present in corresponding *_MASK_BIT_SET. And fill the missing period in
> head comments by the way.
> 
> Signed-off-by: Cao jin <caoj.fnst@...fujitsu.com>
> ---
>  arch/x86/include/asm/cpufeature.h        | 2 --
>  arch/x86/include/asm/disabled-features.h | 1 -
>  arch/x86/include/asm/required-features.h | 3 +--
>  3 files changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
> index 58acda503817..232ffb88039c 100644
> --- a/arch/x86/include/asm/cpufeature.h
> +++ b/arch/x86/include/asm/cpufeature.h
> @@ -81,7 +81,6 @@ extern const char * const x86_bug_flags[NBUGINTS*32];
>  	   CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 16, feature_bit) ||	\
>  	   CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 17, feature_bit) ||	\
>  	   CHECK_BIT_IN_MASK_WORD(REQUIRED_MASK, 18, feature_bit) ||	\
> -	   REQUIRED_MASK_CHECK					  ||	\
>  	   BUILD_BUG_ON_ZERO(NCAPINTS != 19))
>  
>  #define DISABLED_MASK_BIT_SET(feature_bit)				\
> @@ -104,7 +103,6 @@ extern const char * const x86_bug_flags[NBUGINTS*32];
>  	   CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 16, feature_bit) ||	\
>  	   CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 17, feature_bit) ||	\
>  	   CHECK_BIT_IN_MASK_WORD(DISABLED_MASK, 18, feature_bit) ||	\
> -	   DISABLED_MASK_CHECK					  ||	\
>  	   BUILD_BUG_ON_ZERO(NCAPINTS != 19))
>  
>  #define cpu_has(c, bit)							\

If you do a little bit of git archeology:

$ git annotate arch/x86/include/asm/cpufeature.h

after a while, you'll see that this was added in:

1e61f78baf89 ("x86/cpufeature: Make sure DISABLED/REQUIRED macros are updated")

and then you could Cc Dave and ask what he was thinking then?

Leaving in the rest for reference.

> diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
> index a5ea841cc6d2..8a2eafa86739 100644
> --- a/arch/x86/include/asm/disabled-features.h
> +++ b/arch/x86/include/asm/disabled-features.h
> @@ -84,6 +84,5 @@
>  #define DISABLED_MASK16	(DISABLE_PKU|DISABLE_OSPKE|DISABLE_LA57|DISABLE_UMIP)
>  #define DISABLED_MASK17	0
>  #define DISABLED_MASK18	0
> -#define DISABLED_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != 19)
>  
>  #endif /* _ASM_X86_DISABLED_FEATURES_H */
> diff --git a/arch/x86/include/asm/required-features.h b/arch/x86/include/asm/required-features.h
> index 6847d85400a8..cb98b66d3e81 100644
> --- a/arch/x86/include/asm/required-features.h
> +++ b/arch/x86/include/asm/required-features.h
> @@ -1,7 +1,7 @@
>  #ifndef _ASM_X86_REQUIRED_FEATURES_H
>  #define _ASM_X86_REQUIRED_FEATURES_H
>  
> -/* Define minimum CPUID feature set for kernel These bits are checked
> +/* Define minimum CPUID feature set for kernel. These bits are checked
>     really early to actually display a visible error message before the
>     kernel dies.  Make sure to assign features to the proper mask!
>  
> @@ -101,6 +101,5 @@
>  #define REQUIRED_MASK16	0
>  #define REQUIRED_MASK17	0
>  #define REQUIRED_MASK18	0
> -#define REQUIRED_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != 19)
>  
>  #endif /* _ASM_X86_REQUIRED_FEATURES_H */
> -- 
> 2.17.0

-- 
Regards/Gruss,
    Boris.

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