linux-kernel - Re: [PATCH v3 2/2] KVM: x86: Expose CPUID.(EAX=7,ECX=1).EAX[12:10] to the guest

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Message-ID: <Yz+EzB0Y0tRl7rAz@google.com>
Date:   Fri, 7 Oct 2022 01:45:48 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     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>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        "Chang S. Bae" <chang.seok.bae@...el.com>,
        Babu Moger <babu.moger@....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 2/2] KVM: x86: Expose CPUID.(EAX=7,ECX=1).EAX[12:10]
 to the guest

The shortlog is trying to win some kind of award.

And technically, KVM_GET_SUPPORTED_CPUID advertises features to userspace, not
to the guest.  How about this?

  KVM: x86: Advertise fast REP string features inherent to the CPU

On Thu, Sep 01, 2022, Jim Mattson wrote:
> Fast zero-length REP MOVSB, fast short REP STOSB, and fast short REP
> {CMPSB,SCASB} are inherent features of the processor that cannot be
> hidden by the hypervisor. When these features are present on the host,
> enumerate them in KVM_GET_SUPPORTED_CPUID.
> 
> Signed-off-by: Jim Mattson <jmattson@...gle.com>

With a less cryptic shortlog,

Reviewed-by: Sean Christopherson <seanjc@...gle.com>