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

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

On 13/06/2019 10:39, Andrew Murray wrote:
> On Thu, Jun 13, 2019 at 08:30:51AM +0100, Julien Thierry wrote:
>> Hi Andrew,
>>
>> On 12/06/2019 20:04, Andrew Murray wrote:
>>> We currently use pmc->bitmask to determine the width of the pmc - however
>>> it's superfluous as the pmc index already describes if the pmc is a cycle
>>> counter or event counter. The architecture clearly describes the widths of
>>> these counters.
>>>
>>> Let's remove the bitmask to simplify the code.
>>>
>>> Signed-off-by: Andrew Murray <andrew.murray@arm.com>
>>> ---
>>>   include/kvm/arm_pmu.h |  1 -
>>>   virt/kvm/arm/pmu.c    | 19 +++++++++----------
>>>   2 files changed, 9 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
>>> index b73f31baca52..2f0e28dc5a9e 100644
>>> --- a/include/kvm/arm_pmu.h
>>> +++ b/include/kvm/arm_pmu.h
>>> @@ -28,7 +28,6 @@
>>>   struct kvm_pmc {
>>>   	u8 idx;	/* index into the pmu->pmc array */
>>>   	struct perf_event *perf_event;
>>> -	u64 bitmask;
>>>   };
>>>   
>>>   struct kvm_pmu {
>>> diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
>>> 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) ?

Cheers
Suzuki
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