linux-kernel - Re: [PATCH v2 4/4] KVM: x86/vPMU: Add lazy mechanism to release perf

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Message-ID: <2175c2cd-2c1e-22e8-2f67-3fc334ef2a40@redhat.com>
Date:   Mon, 21 Oct 2019 17:28:31 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Like Xu <like.xu@...ux.intel.com>, kvm@...r.kernel.org
Cc:     peterz@...radead.org, Jim Mattson <jmattson@...gle.com>,
        rkrcmar@...hat.com, sean.j.christopherson@...el.com,
        vkuznets@...hat.com, Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        ak@...ux.intel.com, wei.w.wang@...el.com, kan.liang@...el.com,
        like.xu@...el.com, ehankland@...gle.com, arbel.moshe@...cle.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/4] KVM: x86/vPMU: Add lazy mechanism to release
 perf_event per vPMC

On 21/10/19 16:04, Like Xu wrote:
> 
>>
>> 2) introduce a new callback msr_idx_to_pmc that returns a struct
>> kvm_pmc*, and change kvm_pmu_is_valid_msr to do
> 
> For callback msr_idx_to_pmc,
> how do we deal with the input 'MSR_CORE_PERF_FIXED_CTR_CTRL'
> which may return several fixed kvm_pmcs not just one?

For RDMSR, do not do anything.  For WRMSR, you can handle it in the
set_msr callback.

>>
>> static int kvm_pmu_mark_pmc_in_use(struct kvm_vcpu *vcpu, u32 msr)
> 
> s/static int/static void/.
> 
>> {
>>     struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
>>     struct kvm_pmc *pmc = kvm_x86_ops->pmu_ops->msr_idx_to_pmc(vcpu, msr);
> 
> We need 'if(pmc)' here.

Agreed, sorry for the sloppiness.  Never interpret my suggestions as
more than pseudocode. :)

Paolo