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References: <20220302111334.12689-1-likexu@tencent.com> <20220302111334.12689-8-likexu@tencent.com>
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From:   Jim Mattson <jmattson@google.com>
Date:   Mon, 7 Mar 2022 16:36:57 -0800
Message-ID: <CALMp9eQtzS6HEHZ4__K9VuG+-Duwt5uUFb_FcW4DaBKPDmcYkA@mail.gmail.com>
Subject: Re: [PATCH v2 07/12] KVM: x86/pmu: Use PERF_TYPE_RAW to merge
 reprogram_{gp, fixed}counter()
To:     Like Xu <like.xu.linux@gmail.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>, 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>
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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
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.

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