Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <888d5878-a2be-4624-d2c5-227fa19c8150@gmail.com>
Date:   Tue, 8 Mar 2022 19:43:59 +0800
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0)
 Gecko/20100101 Thunderbird/91.6.2
Subject: Re: [PATCH v2 07/12] KVM: x86/pmu: Use PERF_TYPE_RAW to merge
 reprogram_{gp, fixed}counter()
Content-Language: en-US
To:     Jim Mattson <jmattson@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>
Cc:     kvm@vger.kernel.org, Sean Christopherson <seanjc@google.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Joerg Roedel <joro@8bytes.org>, linux-kernel@vger.kernel.org,
        Like Xu <likexu@tencent.com>,
        Peter Zijlstra <peterz@infradead.org>
References: <20220302111334.12689-1-likexu@tencent.com>
 <20220302111334.12689-8-likexu@tencent.com>
 <CALMp9eQtzS6HEHZ4__K9VuG+-Duwt5uUFb_FcW4DaBKPDmcYkA@mail.gmail.com>
From:   Like Xu <like.xu.linux@gmail.com>
Organization: Tencent
In-Reply-To: <CALMp9eQtzS6HEHZ4__K9VuG+-Duwt5uUFb_FcW4DaBKPDmcYkA@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 8/3/2022 8:36 am, Jim Mattson wrote:
> On Wed, Mar 2, 2022 at 3:14 AM Like Xu <like.xu.linux@gmail.com> wrote:
>>
>> From: Like Xu <likexu@tencent.com>
>>
>> The code sketch for reprogram_{gp, fixed}_counter() is similar, while the
>> fixed counter using the PERF_TYPE_HARDWAR type and the gp being
>> able to use either PERF_TYPE_HARDWAR or PERF_TYPE_RAW type
>> depending on the pmc->eventsel value.
>>
>> After 'commit 761875634a5e ("KVM: x86/pmu: Setup pmc->eventsel
>> for fixed PMCs")', the pmc->eventsel of the fixed counter will also have
>> been setup with the same semantic value and will not be changed during
>> the guest runtime. But essentially, "the HARDWARE is just a convenience
>> wrapper over RAW IIRC", quoated from Peterz. So it could be pretty safe
>> to use the PERF_TYPE_RAW type only to program both gp and fixed
>> counters naturally in the reprogram_counter().
>>
>> To make the gp and fixed counters more semantically symmetrical,
>> the selection of EVENTSEL_{USER, OS, INT} bits is temporarily translated
>> via fixed_ctr_ctrl before the pmc_reprogram_counter() call.
>>
>> Cc: Peter Zijlstra <peterz@infradead.org>
>> Suggested-by: Jim Mattson <jmattson@google.com>
>> Signed-off-by: Like Xu <likexu@tencent.com>
>> ---
>>   arch/x86/kvm/pmu.c           | 128 +++++++++++++----------------------
>>   arch/x86/kvm/vmx/pmu_intel.c |   2 +-
>>   2 files changed, 47 insertions(+), 83 deletions(-)
>>
>> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
>> index 5299488b002c..00e1660c10ca 100644
>> --- a/arch/x86/kvm/pmu.c
>> +++ b/arch/x86/kvm/pmu.c
>> @@ -215,85 +215,60 @@ static bool check_pmu_event_filter(struct kvm_pmc *pmc)
>>          return allow_event;
>>   }
>>
>> -static void reprogram_gp_counter(struct kvm_pmc *pmc)
>> -{
>> -       u64 config;
>> -       u32 type = PERF_TYPE_RAW;
>> -       u64 eventsel = pmc->eventsel;
>> -
>> -       if (eventsel & ARCH_PERFMON_EVENTSEL_PIN_CONTROL)
>> -               printk_once("kvm pmu: pin control bit is ignored\n");
>> -
>> -       pmc_pause_counter(pmc);
>> -
>> -       if (!(eventsel & ARCH_PERFMON_EVENTSEL_ENABLE) || !pmc_is_enabled(pmc))
>> -               return;
>> -
>> -       if (!check_pmu_event_filter(pmc))
>> -               return;
>> -
>> -       if (!(eventsel & (ARCH_PERFMON_EVENTSEL_EDGE |
>> -                         ARCH_PERFMON_EVENTSEL_INV |
>> -                         ARCH_PERFMON_EVENTSEL_CMASK |
>> -                         HSW_IN_TX |
>> -                         HSW_IN_TX_CHECKPOINTED))) {
>> -               config = kvm_x86_ops.pmu_ops->pmc_perf_hw_id(pmc);
>> -               if (config != PERF_COUNT_HW_MAX)
>> -                       type = PERF_TYPE_HARDWARE;
>> -       }
>> -
>> -       if (type == PERF_TYPE_RAW)
>> -               config = eventsel & AMD64_RAW_EVENT_MASK;
>> -
>> -       if (pmc->current_config == eventsel && pmc_resume_counter(pmc))
>> -               return;
>> -
>> -       pmc_release_perf_event(pmc);
>> -
>> -       pmc->current_config = eventsel;
>> -       pmc_reprogram_counter(pmc, type, config,
>> -                             !(eventsel & ARCH_PERFMON_EVENTSEL_USR),
>> -                             !(eventsel & ARCH_PERFMON_EVENTSEL_OS),
>> -                             eventsel & ARCH_PERFMON_EVENTSEL_INT,
>> -                             (eventsel & HSW_IN_TX),
>> -                             (eventsel & HSW_IN_TX_CHECKPOINTED));
>> -}
>> -
>> -static void reprogram_fixed_counter(struct kvm_pmc *pmc)
>> +static inline bool pmc_speculative_in_use(struct kvm_pmc *pmc)
>>   {
>>          struct kvm_pmu *pmu = pmc_to_pmu(pmc);
>> -       int idx = pmc->idx - INTEL_PMC_IDX_FIXED;
>> -       u8 ctrl = fixed_ctrl_field(pmu->fixed_ctr_ctrl, idx);
>> -       unsigned en_field = ctrl & 0x3;
>> -       bool pmi = ctrl & 0x8;
>>
>> -       pmc_pause_counter(pmc);
>> +       if (pmc_is_fixed(pmc))
>> +               return fixed_ctrl_field(pmu->fixed_ctr_ctrl,
>> +                       pmc->idx - INTEL_PMC_IDX_FIXED) & 0x3;
>>
>> -       if (!en_field || !pmc_is_enabled(pmc))
>> -               return;
>> -
>> -       if (!check_pmu_event_filter(pmc))
>> -               return;
>> -
>> -       if (pmc->current_config == (u64)ctrl && pmc_resume_counter(pmc))
>> -               return;
>> -
>> -       pmc_release_perf_event(pmc);
>> -
>> -       pmc->current_config = (u64)ctrl;
>> -       pmc_reprogram_counter(pmc, PERF_TYPE_HARDWARE,
>> -                             kvm_x86_ops.pmu_ops->pmc_perf_hw_id(pmc),
>> -                             !(en_field & 0x2), /* exclude user */
>> -                             !(en_field & 0x1), /* exclude kernel */
>> -                             pmi, false, false);
>> +       return pmc->eventsel & ARCH_PERFMON_EVENTSEL_ENABLE;
>>   }
>>
>>   void reprogram_counter(struct kvm_pmc *pmc)
>>   {
>> -       if (pmc_is_gp(pmc))
>> -               reprogram_gp_counter(pmc);
>> -       else
>> -               reprogram_fixed_counter(pmc);
>> +       struct kvm_pmu *pmu = pmc_to_pmu(pmc);
>> +       u64 eventsel = pmc->eventsel;
>> +       u64 new_config = eventsel;
>> +       u8 fixed_ctr_ctrl;
>> +
>> +       pmc_pause_counter(pmc);
>> +
>> +       if (!pmc_speculative_in_use(pmc) || !pmc_is_enabled(pmc))
>> +               return;
>> +
>> +       if (!check_pmu_event_filter(pmc))
>> +               return;
>> +
>> +       if (eventsel & ARCH_PERFMON_EVENTSEL_PIN_CONTROL)
>> +               printk_once("kvm pmu: pin control bit is ignored\n");
>> +
>> +       if (pmc_is_fixed(pmc)) {
>> +               fixed_ctr_ctrl = fixed_ctrl_field(pmu->fixed_ctr_ctrl,
>> +                                                 pmc->idx - INTEL_PMC_IDX_FIXED);
>> +               if (fixed_ctr_ctrl & 0x1)
>> +                       eventsel |= ARCH_PERFMON_EVENTSEL_OS;
>> +               if (fixed_ctr_ctrl & 0x2)
>> +                       eventsel |= ARCH_PERFMON_EVENTSEL_USR;
>> +               if (fixed_ctr_ctrl & 0x8)
>> +                       eventsel |= ARCH_PERFMON_EVENTSEL_INT;
>> +               new_config = (u64)fixed_ctr_ctrl;
>> +       }
>> +
>> +       if (pmc->current_config == new_config && pmc_resume_counter(pmc))
>> +               return;
>> +
>> +       pmc_release_perf_event(pmc);
>> +
>> +       pmc->current_config = new_config;
>> +       pmc_reprogram_counter(pmc, PERF_TYPE_RAW,
>> +                       (eventsel & AMD64_RAW_EVENT_MASK),
>> +                       !(eventsel & ARCH_PERFMON_EVENTSEL_USR),
>> +                       !(eventsel & ARCH_PERFMON_EVENTSEL_OS),
>> +                       eventsel & ARCH_PERFMON_EVENTSEL_INT,
>> +                       (eventsel & HSW_IN_TX),
>> +                       (eventsel & HSW_IN_TX_CHECKPOINTED));
> 
> It seems that this extremely long argument list was motivated by the
> differences between the two original call sites. Now that you have
> mocked up a full eventsel (with USR, OS, INT, IN_TX, and IN_TXCP bits)
> for the fixed counters, why not pass the entire eventsel as the third

I've thought about it.

I'm trying to pass-in generic bits (EVENT_MASK, USER, OS, INT) to
pmc_reprogram_counter() and let the latter handle the implementation details
of assembling the "struct perf_event_attr" to talk carefully with perf core.

I suppose the fixed counters doesn't support IN_TX* bits and I try to
clean those two away in another patch as you know.

In terms of code readability, the current one achieves a good balance.

> argument and drop all of the rest? Then, pmc_reprogram_counter() can
> extract/check the bits of interest.
> 
>>   }
>>   EXPORT_SYMBOL_GPL(reprogram_counter);
>>
>> @@ -451,17 +426,6 @@ void kvm_pmu_init(struct kvm_vcpu *vcpu)
>>          kvm_pmu_refresh(vcpu);
>>   }
>>
>> -static inline bool pmc_speculative_in_use(struct kvm_pmc *pmc)
>> -{
>> -       struct kvm_pmu *pmu = pmc_to_pmu(pmc);
>> -
>> -       if (pmc_is_fixed(pmc))
>> -               return fixed_ctrl_field(pmu->fixed_ctr_ctrl,
>> -                       pmc->idx - INTEL_PMC_IDX_FIXED) & 0x3;
>> -
>> -       return pmc->eventsel & ARCH_PERFMON_EVENTSEL_ENABLE;
>> -}
>> -
>>   /* Release perf_events for vPMCs that have been unused for a full time slice.  */
>>   void kvm_pmu_cleanup(struct kvm_vcpu *vcpu)
>>   {
>> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
>> index 19b78a9d9d47..d823fbe4e155 100644
>> --- a/arch/x86/kvm/vmx/pmu_intel.c
>> +++ b/arch/x86/kvm/vmx/pmu_intel.c
>> @@ -492,7 +492,7 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
>>          pmu->reserved_bits = 0xffffffff00200000ull;
>>
>>          entry = kvm_find_cpuid_entry(vcpu, 0xa, 0);
>> -       if (!entry || !vcpu->kvm->arch.enable_pmu)
>> +       if (!entry || !vcpu->kvm->arch.enable_pmu || !boot_cpu_has(X86_FEATURE_ARCH_PERFMON))
> 
> This change seems unrelated.

The intention of using the PERF_TYPE_HARDWARE type is to emulate guest architecture
PMU on a host without architecture PMU (the oldest Pentium 4), for which the 
guest vPMC
needs to be reprogrammed using the kernel generic perf_hw_id.

This is the most original story of PERF_TYPE_HARDWARE, thanks to history teacher 
Paolo,
who also suggested this way to drop this kind of support.

> 
>>                  return;
>>          eax.full = entry->eax;
>>          edx.full = entry->edx;
>> --
>> 2.35.1
>>