linux-kernel - Re: [PATCH v1 7/8] KVM: x86: Expose PEBS feature to guest

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Message-ID: <20191030095214.GT4097@hirez.programming.kicks-ass.net>
Date:   Wed, 30 Oct 2019 10:52:14 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Kang, Luwei" <luwei.kang@...el.com>
Cc:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "wanpengli@...cent.com" <wanpengli@...cent.com>,
        "jmattson@...gle.com" <jmattson@...gle.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "hpa@...or.com" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>,
        "acme@...nel.org" <acme@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "jolsa@...hat.com" <jolsa@...hat.com>,
        "namhyung@...nel.org" <namhyung@...nel.org>
Subject: Re: [PATCH v1 7/8] KVM: x86: Expose PEBS feature to guest

On Wed, Oct 30, 2019 at 04:07:03AM +0000, Kang, Luwei wrote:
> > > Expose PEBS feature to guest by IA32_MISC_ENABLE[bit12].
> > > IA32_MISC_ENABLE[bit12] is Processor Event Based Sampling (PEBS)
> > > Unavailable (RO) flag:
> > > 1 = PEBS is not supported; 0 = PEBS is supported.
> > 
> > Why does it make sense to expose this on SVM?
> 
> Thanks for the review. This patch won't expose the pebs feature to SVM and return not supported.

AFAICT it exposes/emulates an Intel MSR on AMD, which is just weird.