linux-kernel - Re: [PATCH v3 1/2] x86/cpufeatures: Add macros for Intel's new fast rep string features

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Date:   Thu, 1 Sep 2022 21:14:24 -0700
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Jim Mattson <jmattson@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Babu Moger <babu.moger@....com>,
        "Chang S. Bae" <chang.seok.bae@...el.com>,
        Wyes Karny <wyes.karny@....com>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>,
        "open list:KERNEL VIRTUAL MACHINE FOR X86 (KVM/x86)" 
        <kvm@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] x86/cpufeatures: Add macros for Intel's new fast
 rep string features

On 9/1/22 14:18, Jim Mattson wrote:
> KVM_GET_SUPPORTED_CPUID should reflect these host CPUID bits. The bits
> are already cached in word 12. Give the bits X86_FEATURE names, so
> that they can be easily referenced. Hide these bits from
> /proc/cpuinfo, since the host kernel makes no use of them at present.
> 
> Signed-off-by: Jim Mattson <jmattson@...gle.com>
> ---
>   arch/x86/include/asm/cpufeatures.h | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index ef4775c6db01..454f0faa8e90 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -308,6 +308,9 @@
>   /* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */
>   #define X86_FEATURE_AVX_VNNI		(12*32+ 4) /* AVX VNNI instructions */
>   #define X86_FEATURE_AVX512_BF16		(12*32+ 5) /* AVX512 BFLOAT16 instructions */
> +#define X86_FEATURE_FZRM		(12*32+10) /* "" Fast zero-length REP MOVSB */
> +#define X86_FEATURE_FSRS		(12*32+11) /* "" Fast short REP STOSB */
> +#define X86_FEATURE_FSRC		(12*32+12) /* "" Fast short REP {CMPSB,SCASB} */
>   
>   /* AMD-defined CPU features, CPUID level 0x80000008 (EBX), word 13 */
>   #define X86_FEATURE_CLZERO		(13*32+ 0) /* CLZERO instruction */

Any reason why these bits are hidden from /proc/cpuinfo?

	-hpa