linux-kernel - Re: [PATCH 01/74] x86/cpu/vfm: Add/initialize x86_vfm field to struct cpuinfo

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Message-ID: <20240328164811.GDZgWfSzAWZXO7dUky@fat_crate.local>
Date: Thu, 28 Mar 2024 17:48:11 +0100
From: Borislav Petkov <bp@...en8.de>
To: Tony Luck <tony.luck@...el.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/74] x86/cpu/vfm: Add/initialize x86_vfm field to
 struct cpuinfo_x86

On Thu, Mar 28, 2024 at 09:37:44AM -0700, Tony Luck wrote:
> Refactor struct cpuinfo_x86 so that the vendor, family, and model
> fields are overlayed in a union with a 32-bit field that combines
> all three (together with a one byte reserved field in the upper
> byte).
> 
> This will make it easy, cheap, and reliable to check all three
> values at once.
> 
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
>  arch/x86/include/asm/processor.h | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index 811548f131f4..87115e5d884f 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -108,9 +108,15 @@ struct cpuinfo_topology {
>  };
>  
>  struct cpuinfo_x86 {
> -	__u8			x86;		/* CPU family */
> -	__u8			x86_vendor;	/* CPU vendor */
> -	__u8			x86_model;
> +	union {
> +		struct {
> +			__u8	x86_vendor;	/* CPU vendor */
> +			__u8	x86;		/* CPU family */
> +			__u8	x86_model;
> +			__u8	x86_reserved;
> +		};
> +		__u32		x86_vfm;	/* combined vendor, family, model */
> +	};
>  	__u8			x86_stepping;

Why are you leaving out stepping?

And since we want to simplify all this, why aren't we replacing all
f/m/s checks by using the whole CPUID(1).EAX u32 instead?

Then the macros need to build that CPUID leaf simply.

-- 
Regards/Gruss,
    Boris.

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