Re: [Qemu-devel] [PATCH v2 2/2] kvm: migrate vPMU state

[Paolo Bonzini]

Il 28/07/2013 14:57, Gleb Natapov ha scritto:
>> @@ -1114,6 +1135,33 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
>>              kvm_msr_entry_set(&msrs[n++], MSR_KVM_STEAL_TIME,
>>                                env->steal_time_msr);
>>          }
>> +        if (has_msr_architectural_pmu) {
>> +            /* Stop the counter.  */
>> +            kvm_msr_entry_set(&msrs[n++], MSR_CORE_PERF_FIXED_CTR_CTRL, 0);
>> +            kvm_msr_entry_set(&msrs[n++], MSR_CORE_PERF_GLOBAL_CTRL, 0);
>> +
> Why is this needed?

In v1 it was in the commit message.  I'll fix it up before applying:

> Second, to avoid any possible side effects during the setting of MSRs
> I stop the PMU while setting the counters and event selector MSRs.
> Stopping the PMU snapshots the counters and ensures that no strange
> races can happen if the counters were saved close to their overflow
> value.

Paolo