linux-kernel - Re: [PATCH 2/3] KVM: vPMU: Fill get_msr MSR_CORE_PERF_GLOBAL_OVF

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Date:   Fri, 8 Oct 2021 19:17:39 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Like Xu <like.xu.linux@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 2/3] KVM: vPMU: Fill get_msr MSR_CORE_PERF_GLOBAL_OVF_CTRL
 w/ 0

On Fri, 8 Oct 2021 at 19:02, Like Xu <like.xu.linux@...il.com> wrote:
>
> cc Andi,
>
> On 8/10/2021 5:57 pm, Wanpeng Li wrote:
> > From: Wanpeng Li <wanpengli@...cent.com>
> >
> > SDM section 18.2.3 mentioned that:
> >
> >    "IA32_PERF_GLOBAL_OVF_CTL MSR allows software to clear overflow indicator(s) of
> >     any general-purpose or fixed-function counters via a single WRMSR."
> >
> > It is R/W mentioned by SDM, we read this msr on bare-metal during perf testing,
> > the value is always 0 for CLX/SKX boxes on hands. Let's fill get_msr
> > MSR_CORE_PERF_GLOBAL_OVF_CTRL w/ 0 as hardware behavior.
> >
> > Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> > ---
> > Btw, xen also fills get_msr MSR_CORE_PERF_GLOBAL_OVF_CTRL 0.
> >
> >   arch/x86/kvm/vmx/pmu_intel.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> > index 10cc4f65c4ef..47260a8563f9 100644
> > --- a/arch/x86/kvm/vmx/pmu_intel.c
> > +++ b/arch/x86/kvm/vmx/pmu_intel.c
> > @@ -365,7 +365,7 @@ static int intel_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> >               msr_info->data = pmu->global_ctrl;
> >               return 0;
> >       case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
> > -             msr_info->data = pmu->global_ovf_ctrl;
> > +             msr_info->data = 0;
>
> Tested-by: Like Xu <likexu@...cent.com>

Thanks.

> Further, better to drop 'u64 global_ovf_ctrl' directly.

Good suggestion. :)

    Wanpeng