linux-kernel - Re: [PATCH v11 08/11] KVM: x86/pmu: Emulate LBR feature via guest LBR event

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Date:   Tue, 19 May 2020 20:40:07 +0800
From:   "Xu, Like" <like.xu@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Like Xu <like.xu@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>, ak@...ux.intel.com,
        wei.w.wang@...el.com
Subject: Re: [PATCH v11 08/11] KVM: x86/pmu: Emulate LBR feature via guest LBR
 event

On 2020/5/19 19:03, Peter Zijlstra wrote:
> On Thu, May 14, 2020 at 04:30:51PM +0800, Like Xu wrote:
>> @@ -6698,6 +6698,7 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
>>   
>>   	if (vcpu_to_pmu(vcpu)->version)
>>   		atomic_switch_perf_msrs(vmx);
>> +
>>   	atomic_switch_umwait_control_msr(vmx);
>>   
>>   	if (enable_preemption_timer)
> Is this where the test to see if any of the KVM events went into ERROR
> state should go?
Yes, I chose the same location to do LBR availability check in the next 
patch 0010.

Actually for normal vPMU counters and their events,
I'm not sure whether pr_warn() should also be used widely.

The current approach is to keep vPMC silent when it may be inaccurate.

I may need @Paolo's attitude on this issue.

Thanks,
Like Xu
>
> 	if (event->state == PERF_EVENT_STATE_ERROR) {
> 		pr_warn("unhappy, someone stole our counter\n");
> 	}
>
> like..