Re: [PATCH 6/6] KVM: arm64: Upgrade PMU support to ARMv8.4

Auger Eric
2021-01-15T17:28:18Z

Hi Marc,

On 1/15/21 5:42 PM, Marc Zyngier wrote:
> Hi Eric,
>
> On 2021-01-15 14:01, Auger Eric wrote:
>> Hi Marc,
>>
>> On 1/14/21 11:56 AM, Marc Zyngier wrote:
>>> Upgrading the PMU code from ARMv8.1 to ARMv8.4 turns out to be
>>> pretty easy. All that is required is support for PMMIR_EL1, which
>>> is read-only, and for which returning 0 is a valid option.
>>>
>>> Let's just do that and adjust what we return to the guest.
>>>
>>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>>> ---
>>>  arch/arm64/kvm/sys_regs.c | 5 +++--
>>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>>> index 8f79ec1fffa7..2f4ecbd2abfb 100644
>>> --- a/arch/arm64/kvm/sys_regs.c
>>> +++ b/arch/arm64/kvm/sys_regs.c
>>> @@ -1051,10 +1051,10 @@ static u64 read_id_reg(const struct kvm_vcpu
>>> *vcpu,
>>>          /* Limit debug to ARMv8.0 */
>>>          val &= ~FEATURE(ID_AA64DFR0_DEBUGVER);
>>>          val |= FIELD_PREP(FEATURE(ID_AA64DFR0_DEBUGVER), 6);
>>> -        /* Limit guests to PMUv3 for ARMv8.1 */
>>> +        /* Limit guests to PMUv3 for ARMv8.4 */
>>>          val = cpuid_feature_cap_perfmon_field(val,
>>>                                ID_AA64DFR0_PMUVER_SHIFT,
>>> -                              kvm_vcpu_has_pmu(vcpu) ?
>>> ID_AA64DFR0_PMUVER_8_1 : 0);
>>> +                              kvm_vcpu_has_pmu(vcpu) ?
>>> ID_AA64DFR0_PMUVER_8_4 : 0);
>>>          break;
>>>      case SYS_ID_DFR0_EL1:
>>>          /* Limit guests to PMUv3 for ARMv8.1 */
>> what about the debug version in aarch32 state. Is it on purpose that you
>> leave it as 8_1?
>
> That's a good point. There is also the fact that we keep reporting
> STALL_SLOT as a valid event even in PMCEID0_EL1 despite PMMIR_EL1.SLOTS
> always reporting 0.
Hum OK. I did not notice that ;-)

Thanks

Eric
>
> I'll fix that and resend something next week.
>
> Thanks,
>
>         M.