linux-kernel - RE: [PATCH v1 3/8] KVM: x86: Allocate performance counter for PEBS event

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Message-ID: <82D7661F83C1A047AF7DC287873BF1E173835B1A@SHSMSX104.ccr.corp.intel.com>
Date:   Wed, 30 Oct 2019 04:06:36 +0000
From:   "Kang, Luwei" <luwei.kang@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
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>,
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        "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 3/8] KVM: x86: Allocate performance counter for PEBS
 event

> >  static void pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type,
> >  				  unsigned config, bool exclude_user,
> >  				  bool exclude_kernel, bool intr,
> > -				  bool in_tx, bool in_tx_cp)
> > +				  bool in_tx, bool in_tx_cp, bool pebs)
> >  {
> >  	struct perf_event *event;
> >  	struct perf_event_attr attr = {
> > @@ -111,9 +111,12 @@ static void pmc_reprogram_counter(struct kvm_pmc *pmc, u32 type,
> >  		.exclude_user = exclude_user,
> >  		.exclude_kernel = exclude_kernel,
> >  		.config = config,
> > +		.precise_ip = pebs ? 1 : 0,
> > +		.aux_output = pebs ? 1 : 0,
> 
> srsly?

Hi Peter,
    Thanks for review. For aux_output, I think it should be set 1 when the guest wants to enabled PEBS by Intel PT.
     For precise_ip, it is the precise level in perf and set by perf command line in KVM guest, this may not reflect the accurate value (can be 0~3) here. Here set to 1 is used to allocate a counter for PEBS event and set the MSR_IA32_PEBS_ENABLE register. For PMU virtualization, KVM will trap the guest's write operation to PMU registers and allocate/free event counter from host if a counter enable/disable in guest. We can't always deduce the exact parameter of perf command line from the value of the guest writers to the register.

Thanks,
Luwei Kang