linux-kernel - Re: [PATCH] KVM: x86/pmu: Distinguish EVENTSEL bitmasks for uniform event creation and filtering

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Message-ID: <ebd57e6b-c4c4-cdd5-6bd0-c872f2e0382d@gmail.com>
Date:   Thu, 17 Feb 2022 17:05:36 +0800
From:   Like Xu <like.xu.linux@...il.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86/pmu: Distinguish EVENTSEL bitmasks for uniform
 event creation and filtering

On 10/2/2022 10:09 pm, Jim Mattson wrote:
> On Thu, Feb 10, 2022 at 2:26 AM Like Xu <like.xu.linux@...il.com> wrote:
>>
>> From: Like Xu <likexu@...cent.com>
>>
>> The current usage of EVENTSEL_* macro is a mess in the KVM context. Partly
>> because we have a conceptual ambiguity when choosing to create a RAW or
>> HARDWARE event: when bits other than HARDWARE_EVENT_MASK are set,
>> the pmc_reprogram_counter() will use the RAW type.
>>
>> By introducing the new macro AMD64_EXTRA_EVENTSEL_EVENT to simplify,
>> the following three issues can be addressed in one go:
>>
>> - the 12 selection bits are used as comparison keys for allow or deny;
>> - NON_HARDWARE_EVENT_MASK is only used to determine if a HARDWARE
>>    event is programmed or not, a 12-bit selected event will be a RAW event;
>>    (jmattson helped report this issue)
>> - by reusing AMD64_RAW_EVENT_MASK, the extra 4 selection bits (if set) are
>>    passed to the perf correctly and not filtered out by X86_RAW_EVENT_MASK;.
>>
>> Signed-off-by: Like Xu <likexu@...cent.com>
>> ---
>>   arch/x86/include/asm/perf_event.h |  3 ++-
>>   arch/x86/kvm/pmu.c                | 11 ++++-------
>>   arch/x86/kvm/pmu.h                |  6 ++++++
>>   3 files changed, 12 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
>> index 8fc1b5003713..bd068fd19043 100644
>> --- a/arch/x86/include/asm/perf_event.h
>> +++ b/arch/x86/include/asm/perf_event.h
>> @@ -43,8 +43,9 @@
>>   #define AMD64_EVENTSEL_INT_CORE_SEL_MASK               \
>>          (0xFULL << AMD64_EVENTSEL_INT_CORE_SEL_SHIFT)
>>
>> +#define AMD64_EXTRA_EVENTSEL_EVENT                             (0x0FULL << 32)
>>   #define AMD64_EVENTSEL_EVENT   \
>> -       (ARCH_PERFMON_EVENTSEL_EVENT | (0x0FULL << 32))
>> +       (ARCH_PERFMON_EVENTSEL_EVENT | AMD64_EXTRA_EVENTSEL_EVENT)
>>   #define INTEL_ARCH_EVENT_MASK  \
>>          (ARCH_PERFMON_EVENTSEL_UMASK | ARCH_PERFMON_EVENTSEL_EVENT)
>>
>> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
>> index 2c98f3ee8df4..99426a8d7f18 100644
>> --- a/arch/x86/kvm/pmu.c
>> +++ b/arch/x86/kvm/pmu.c
>> @@ -198,7 +198,8 @@ void reprogram_gp_counter(struct kvm_pmc *pmc, u64 eventsel)
>>
>>          filter = srcu_dereference(kvm->arch.pmu_event_filter, &kvm->srcu);
>>          if (filter) {
>> -               __u64 key = eventsel & AMD64_RAW_EVENT_MASK_NB;
>> +               __u64 key = eventsel & (INTEL_ARCH_EVENT_MASK |
>> +                                       AMD64_EXTRA_EVENTSEL_EVENT);
>>
>>                  if (bsearch(&key, filter->events, filter->nevents,
>>                              sizeof(__u64), cmp_u64))
>> @@ -209,18 +210,14 @@ void reprogram_gp_counter(struct kvm_pmc *pmc, u64 eventsel)
>>          if (!allow_event)
>>                  return;
>>
>> -       if (!(eventsel & (ARCH_PERFMON_EVENTSEL_EDGE |
>> -                         ARCH_PERFMON_EVENTSEL_INV |
>> -                         ARCH_PERFMON_EVENTSEL_CMASK |
>> -                         HSW_IN_TX |
>> -                         HSW_IN_TX_CHECKPOINTED))) {
>> +       if (!(eventsel & NON_HARDWARE_EVENT_MASK)) {
> 
> I still don't understand why we even bother doing this lookup in the
> first place. What's wrong with simply requesting PERF_TYPE_RAW every
> time?

Thanks for the constant chasing, I finally got a reply from Peterz:
"think so; the HARDWARE is just a convenience wrapper over RAW IIRC".

Let me take this step and clean it up a bit.