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

Marc Zyngier
2021-01-15T16:43:28Z

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.

I'll fix that and resend something next week.

Thanks,

M.
--
Jazz is not dead. It just smells funny...