[RFC PATCH 10/43] powerpc/64s: Always set PMU control registers to frozen/disabled when not in use

[Nicholas Piggin]

Excerpts from Nicholas Piggin's message of July 12, 2021 12:41 pm:
> Excerpts from Athira Rajeev's message of July 10, 2021 12:50 pm:
>> 
>> 
>>> On 22-Jun-2021, at 4:27 PM, Nicholas Piggin <npiggin at gmail.com> wrote:
>>> 
>>> KVM PMU management code looks for particular frozen/disabled bits in
>>> the PMU registers so it knows whether it must clear them when coming
>>> out of a guest or not. Setting this up helps KVM make these optimisations
>>> without getting confused. Longer term the better approach might be to
>>> move guest/host PMU switching to the perf subsystem.
>>> 
>>> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
>>> ---
>>> arch/powerpc/kernel/cpu_setup_power.c | 4 ++--
>>> arch/powerpc/kernel/dt_cpu_ftrs.c     | 6 +++---
>>> arch/powerpc/kvm/book3s_hv.c          | 5 +++++
>>> arch/powerpc/perf/core-book3s.c       | 7 +++++++
>>> 4 files changed, 17 insertions(+), 5 deletions(-)
>>> 
>>> diff --git a/arch/powerpc/kernel/cpu_setup_power.c b/arch/powerpc/kernel/cpu_setup_power.c
>>> index a29dc8326622..3dc61e203f37 100644
>>> --- a/arch/powerpc/kernel/cpu_setup_power.c
>>> +++ b/arch/powerpc/kernel/cpu_setup_power.c
>>> @@ -109,7 +109,7 @@ static void init_PMU_HV_ISA207(void)
>>> static void init_PMU(void)
>>> {
>>> 	mtspr(SPRN_MMCRA, 0);
>>> -	mtspr(SPRN_MMCR0, 0);
>>> +	mtspr(SPRN_MMCR0, MMCR0_FC);
>>> 	mtspr(SPRN_MMCR1, 0);
>>> 	mtspr(SPRN_MMCR2, 0);
>>> }
>>> @@ -123,7 +123,7 @@ static void init_PMU_ISA31(void)
>>> {
>>> 	mtspr(SPRN_MMCR3, 0);
>>> 	mtspr(SPRN_MMCRA, MMCRA_BHRB_DISABLE);
>>> -	mtspr(SPRN_MMCR0, MMCR0_PMCCEXT);
>>> +	mtspr(SPRN_MMCR0, MMCR0_FC | MMCR0_PMCCEXT);
>>> }
>>> 
>>> /*
>>> diff --git a/arch/powerpc/kernel/dt_cpu_ftrs.c b/arch/powerpc/kernel/dt_cpu_ftrs.c
>>> index 0a6b36b4bda8..06a089fbeaa7 100644
>>> --- a/arch/powerpc/kernel/dt_cpu_ftrs.c
>>> +++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
>>> @@ -353,7 +353,7 @@ static void init_pmu_power8(void)
>>> 	}
>>> 
>>> 	mtspr(SPRN_MMCRA, 0);
>>> -	mtspr(SPRN_MMCR0, 0);
>>> +	mtspr(SPRN_MMCR0, MMCR0_FC);
>>> 	mtspr(SPRN_MMCR1, 0);
>>> 	mtspr(SPRN_MMCR2, 0);
>>> 	mtspr(SPRN_MMCRS, 0);
>>> @@ -392,7 +392,7 @@ static void init_pmu_power9(void)
>>> 		mtspr(SPRN_MMCRC, 0);
>>> 
>>> 	mtspr(SPRN_MMCRA, 0);
>>> -	mtspr(SPRN_MMCR0, 0);
>>> +	mtspr(SPRN_MMCR0, MMCR0_FC);
>>> 	mtspr(SPRN_MMCR1, 0);
>>> 	mtspr(SPRN_MMCR2, 0);
>>> }
>>> @@ -428,7 +428,7 @@ static void init_pmu_power10(void)
>>> 
>>> 	mtspr(SPRN_MMCR3, 0);
>>> 	mtspr(SPRN_MMCRA, MMCRA_BHRB_DISABLE);
>>> -	mtspr(SPRN_MMCR0, MMCR0_PMCCEXT);
>>> +	mtspr(SPRN_MMCR0, MMCR0_FC | MMCR0_PMCCEXT);
>>> }
>>> 
>>> static int __init feat_enable_pmu_power10(struct dt_cpu_feature *f)
>>> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
>>> index 1f30f98b09d1..f7349d150828 100644
>>> --- a/arch/powerpc/kvm/book3s_hv.c
>>> +++ b/arch/powerpc/kvm/book3s_hv.c
>>> @@ -2593,6 +2593,11 @@ static int kvmppc_core_vcpu_create_hv(struct kvm_vcpu *vcpu)
>>> #endif
>>> #endif
>>> 	vcpu->arch.mmcr[0] = MMCR0_FC;
>>> +	if (cpu_has_feature(CPU_FTR_ARCH_31)) {
>>> +		vcpu->arch.mmcr[0] |= MMCR0_PMCCEXT;
>>> +		vcpu->arch.mmcra = MMCRA_BHRB_DISABLE;
>>> +	}
>>> +
>>> 	vcpu->arch.ctrl = CTRL_RUNLATCH;
>>> 	/* default to host PVR, since we can't spoof it */
>>> 	kvmppc_set_pvr_hv(vcpu, mfspr(SPRN_PVR));
>>> diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
>>> index 51622411a7cc..e33b29ec1a65 100644
>>> --- a/arch/powerpc/perf/core-book3s.c
>>> +++ b/arch/powerpc/perf/core-book3s.c
>>> @@ -1361,6 +1361,13 @@ static void power_pmu_enable(struct pmu *pmu)
>>> 		goto out;
>>> 
>>> 	if (cpuhw->n_events == 0) {
>>> +		if (cpu_has_feature(CPU_FTR_ARCH_31)) {
>>> +			mtspr(SPRN_MMCRA, MMCRA_BHRB_DISABLE);
>>> +			mtspr(SPRN_MMCR0, MMCR0_FC | MMCR0_PMCCEXT);
>>> +		} else {
>>> +			mtspr(SPRN_MMCRA, 0);
>>> +			mtspr(SPRN_MMCR0, MMCR0_FC);
>>> +		}
>> 
>> 
>> Hi Nick,
>> 
>> We are setting these bits in “power_pmu_disable” function. And disable will be called before any event gets deleted/stopped. Can you please help to understand why this is needed in power_pmu_enable path also ?
> 
> I'll have to go back and check what I needed it for.

Okay, MMCRA is getting MMCRA_SDAR_MODE_DCACHE set on POWER9, by the looks.

That's not necessarily a problem, but KVM sets MMCRA to 0 to disable
SDAR updates. So KVM and perf don't agree on what the "correct" value
for disabled is. Which could be a problem with POWER10 not setting BHRB
disable before my series.

I'll get rid of this hunk for now, I expect things won't be exactly clean
or consistent until the KVM host PMU code is moved into perf/ though.

Thanks,
Nick