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Date:   Thu, 3 Feb 2022 12:25:43 -0800
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To:     Jim Mattson <jmattson@google.com>,
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References: <20220203194308.2469117-1-jmattson@google.com>
 <20220203194308.2469117-2-jmattson@google.com>
From:   Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCH 2/2] x86/cpufeatures: Add macros for Intel's new fast rep
 string features
In-Reply-To: <20220203194308.2469117-2-jmattson@google.com>
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On 2/3/22 11:43, Jim Mattson wrote:
> Even if no one else cares, these features should be exposed to kvm
> guests, and the code for the KVM_GET_SUPPORTED_CPUID ioctl is more
> readable if the bits have corresponding X86_FEATURE macros.

I went digging around KVM_GET_SUPPORTED_CPUID and didn't see any obvious
unreadable things resulting from not having these defines.  Maybe I'm
looking in the wrong spot.  Do you have a slightly more specific pointer?

> +#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} */

If the use really is for inside the kernel, maybe we should hide them
from cpuinfo:

#define X86_FEATURE_FSRC		(12*32+12) /* "" Fast short REP {CMPSB,SCASB} */