linux-kernel - Re: [PATCH v6 04/16] KVM: x86/pmu: Set MSR_IA32_MISC_ENABLE

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Date:   Mon, 17 May 2021 21:19:00 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Venkatesh Srinivas <venkateshs@...omium.org>
Cc:     "Xu, Like" <like.xu@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, weijiang.yang@...el.com,
        Kan Liang <kan.liang@...ux.intel.com>, ak@...ux.intel.com,
        wei.w.wang@...el.com, Stephane Eranian <eranian@...gle.com>,
        liuxiangdong5@...wei.com, linux-kernel@...r.kernel.org,
        x86@...nel.org, kvm@...r.kernel.org, Yao Yuan <yuan.yao@...el.com>,
        Like Xu <like.xu@...ux.intel.com>
Subject: Re: [PATCH v6 04/16] KVM: x86/pmu: Set MSR_IA32_MISC_ENABLE_EMON bit
 when vPMU is enabled

On Mon, May 17, 2021, Venkatesh Srinivas wrote:
> Should this bit be conditional on the host having it set?

No need, KVM advertises the architectural PMU to userspace iff hardware itself
has an architecture PMU.  Userspace is free to lie to its guests so long as doing
so doesn't put KVM at risk.