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Subject: Re: [PATCH v2 4/4] KVM: x86/vPMU: Add lazy mechanism to release
 perf_event per vPMC
To:     Like Xu <like.xu@linux.intel.com>, kvm@vger.kernel.org
Cc:     peterz@infradead.org, Jim Mattson <jmattson@google.com>,
        rkrcmar@redhat.com, sean.j.christopherson@intel.com,
        vkuznets@redhat.com, Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        ak@linux.intel.com, wei.w.wang@intel.com, kan.liang@intel.com,
        like.xu@intel.com, ehankland@google.com, arbel.moshe@oracle.com,
        linux-kernel@vger.kernel.org
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 <5eb638a3-5ebe-219a-c975-19808ab702b9@redhat.com>
 <c2979d05-4536-e3b5-e2f6-3e6740c1a82d@linux.intel.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
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Date:   Mon, 21 Oct 2019 17:28:31 +0200
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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