Re: [PATCH v9 4/5] KVM: arm/arm64: remove pmc->bitmask

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 17/06/2019 16:43, Andrew Murray wrote:
> On Thu, Jun 13, 2019 at 05:50:43PM +0100, Suzuki K Poulose wrote:
>>
>>
>> On 13/06/2019 10:39, Andrew Murray wrote:
>>> On Thu, Jun 13, 2019 at 08:30:51AM +0100, Julien Thierry wrote:

>>>>> index ae1e886d4a1a..88ce24ae0b45 100644
>>>>> --- a/virt/kvm/arm/pmu.c
>>>>> +++ b/virt/kvm/arm/pmu.c
>>>>> @@ -47,7 +47,10 @@ u64 kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu, u64 select_idx)
>>>>>    		counter += perf_event_read_value(pmc->perf_event, &enabled,
>>>>>    						 &running);
>>>>> -	return counter & pmc->bitmask;
>>>>> +	if (select_idx != ARMV8_PMU_CYCLE_IDX)
>>>>> +		counter = lower_32_bits(counter);
>>>>
>>>> Shouldn't this depend on PMCR.LC as well? If PMCR.LC is clear we only
>>>> want the lower 32bits of the cycle counter.
>>>
>>> Yes that's correct. The hunk should look like this:
>>>
>>> -       return counter & pmc->bitmask;
>>> +       if (!(select_idx == ARMV8_PMU_CYCLE_IDX &&
>>> +             __vcpu_sys_reg(vcpu, PMCR_EL0) & ARMV8_PMU_PMCR_LC))
>>> +               counter = lower_32_bits(counter);
>>> +
>>> +       return counter;
>>
>> May be you could add a macro :
>>
>> #define vcpu_pmu_counter_is_64bit(vcpu, idx) ?
> 
> Yes I think a helper would be useful - though I'd prefer the name
> 'kvm_pmu_idx_is_long_cycle_counter'. This seems a little clearer as
> you could otherwise argue that a chained counter is also 64 bits.

When you get to add 64bit PMU counter (v8.5), this would be handy. So
having it de-coupled from the cycle counter may be a good idea. Anyways,
I leave that to you.

Cheers
Suzuki
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