linux-kernel - Re: [RFC v1 1/9] KVM: x86: Add base address parameter for get_fixed

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Date:   Thu, 29 Aug 2019 12:01:34 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Luwei Kang <luwei.kang@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [RFC v1 1/9] KVM: x86: Add base address parameter for
 get_fixed_pmc function

On Wed, Aug 28, 2019 at 10:38 PM Luwei Kang <luwei.kang@...el.com> wrote:
>
> PEBS output Inte PT introduces some new MSRs (MSR_RELOAD_FIXED_CTRx)
> for fixed function counters that use for autoload the preset value
> after writing out a PEBS event.
>
> Introduce base MSRs address parameter to make this function can get
> performance monitor counter structure by MSR_RELOAD_FIXED_CTRx registers.
>
> Signed-off-by: Luwei Kang <luwei.kang@...el.com>
> ---
>  arch/x86/kvm/pmu.h           |  5 ++---
>  arch/x86/kvm/vmx/pmu_intel.c | 14 +++++++++-----
>  2 files changed, 11 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h
> index 58265f7..c62a1ff 100644
> --- a/arch/x86/kvm/pmu.h
> +++ b/arch/x86/kvm/pmu.h
> @@ -93,10 +93,9 @@ static inline struct kvm_pmc *get_gp_pmc(struct kvm_pmu *pmu, u32 msr,
>  }
>
>  /* returns fixed PMC with the specified MSR */
> -static inline struct kvm_pmc *get_fixed_pmc(struct kvm_pmu *pmu, u32 msr)
> +static inline struct kvm_pmc *get_fixed_pmc(struct kvm_pmu *pmu, u32 msr,
> +                                                               int base)
>  {
> -       int base = MSR_CORE_PERF_FIXED_CTR0;
> -
>         if (msr >= base && msr < base + pmu->nr_arch_fixed_counters)
>                 return &pmu->fixed_counters[msr - base];

IIUC, these new MSRs aren't new fixed PMCs, but are values to be
reloaded into the existing fixed PMCs when a PEBS event has been
written. This change makes it look like you are introducing an
additional set of fixed PMCs.