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Date: Thu, 16 Apr 2020 22:40:34 +0800
From: Like Xu <like.xu@...ux.intel.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: Andi Kleen <ak@...ux.intel.com>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86/pmu: Support full width counting
Hi Paolo,
If there is anything needs to be improved for this patch,
please let me know.
Thanks,
Like Xu
On 2020/4/8 21:53, Like Xu wrote:
> Intel CPUs have a new alternative MSR range (starting from MSR_IA32_PMC0)
> for GP counters that allows writing the full counter width. Enable this
> range from a new capability bit (IA32_PERF_CAPABILITIES.FW_WRITE[bit 13]).
>
> The perf driver queries CPUID to get the counter width, and sign extends
> the counter values as needed. The traditional MSRs always limit to 32bit,
> even though the counter internally is larger (usually 48 bits).
>
> When the new capability is set, use the alternative range which do not
> have these restrictions. This lowers the overhead of perf stat slightly
> because it has to do less interrupts to accumulate the counter value.
>
> Signed-off-by: Like Xu <like.xu@...ux.intel.com>
> ---
> arch/x86/include/asm/kvm_host.h | 1 +
> arch/x86/kvm/vmx/capabilities.h | 15 +++++++++++++
> arch/x86/kvm/vmx/pmu_intel.c | 38 +++++++++++++++++++++++++++------
> arch/x86/kvm/vmx/vmx.c | 2 ++
> 4 files changed, 50 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 42a2d0d3984a..1c2e3e79490b 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -481,6 +481,7 @@ struct kvm_pmu {
> u64 counter_bitmask[2];
> u64 global_ctrl_mask;
> u64 global_ovf_ctrl_mask;
> + u64 perf_capabilities;
> u64 reserved_bits;
> u8 version;
> struct kvm_pmc gp_counters[INTEL_PMC_MAX_GENERIC];
> diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
> index 8903475f751e..3624568633bd 100644
> --- a/arch/x86/kvm/vmx/capabilities.h
> +++ b/arch/x86/kvm/vmx/capabilities.h
> @@ -367,4 +367,19 @@ static inline bool vmx_pt_mode_is_host_guest(void)
> return pt_mode == PT_MODE_HOST_GUEST;
> }
>
> +#define PMU_CAP_FW_WRITE (1ULL << 13)
> +
> +static inline u64 vmx_supported_perf_capabilities(void)
> +{
> + u64 perf_cap = 0;
> +
> + if (boot_cpu_has(X86_FEATURE_PDCM))
> + rdmsrl(MSR_IA32_PERF_CAPABILITIES, perf_cap);
> +
> + /* Currently, KVM only support Full-Width Writes. */
> + perf_cap &= PMU_CAP_FW_WRITE;
> +
> + return perf_cap;
> +}
> +
> #endif /* __KVM_X86_VMX_CAPS_H */
> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> index 7c857737b438..99563d1ec854 100644
> --- a/arch/x86/kvm/vmx/pmu_intel.c
> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> @@ -150,6 +150,12 @@ static struct kvm_pmc *intel_rdpmc_ecx_to_pmc(struct kvm_vcpu *vcpu,
> return &counters[array_index_nospec(idx, num_counters)];
> }
>
> +static inline bool full_width_writes_is_enabled(struct kvm_pmu *pmu)
> +{
> + return (vmx_supported_perf_capabilities() & PMU_CAP_FW_WRITE) &&
> + (pmu->perf_capabilities & PMU_CAP_FW_WRITE);
> +}
> +
> static bool intel_is_valid_msr(struct kvm_vcpu *vcpu, u32 msr)
> {
> struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
> @@ -162,10 +168,15 @@ static bool intel_is_valid_msr(struct kvm_vcpu *vcpu, u32 msr)
> case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
> ret = pmu->version > 1;
> break;
> + case MSR_IA32_PERF_CAPABILITIES:
> + ret = guest_cpuid_has(vcpu, X86_FEATURE_PDCM);
> + break;
> default:
> ret = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0) ||
> get_gp_pmc(pmu, msr, MSR_P6_EVNTSEL0) ||
> - get_fixed_pmc(pmu, msr);
> + get_fixed_pmc(pmu, msr) ||
> + (get_gp_pmc(pmu, msr, MSR_IA32_PMC0) &&
> + full_width_writes_is_enabled(pmu));
> break;
> }
>
> @@ -202,8 +213,12 @@ static int intel_pmu_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *data)
> case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
> *data = pmu->global_ovf_ctrl;
> return 0;
> + case MSR_IA32_PERF_CAPABILITIES:
> + *data = pmu->perf_capabilities;
> + return 0;
> default:
> - if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0))) {
> + if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0))
> + || (pmc = get_gp_pmc(pmu, msr, MSR_IA32_PMC0))) {
> u64 val = pmc_read_counter(pmc);
> *data = val & pmu->counter_bitmask[KVM_PMC_GP];
> return 0;
> @@ -258,9 +273,13 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> return 0;
> }
> break;
> + case MSR_IA32_PERF_CAPABILITIES:
> + return 1; /* RO MSR */
> default:
> - if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0))) {
> - if (!msr_info->host_initiated)
> + if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0))
> + || (pmc = get_gp_pmc(pmu, msr, MSR_IA32_PMC0))) {
> + if (!msr_info->host_initiated &&
> + !full_width_writes_is_enabled(pmu))
> data = (s64)(s32)data;
> pmc->counter += data - pmc_read_counter(pmc);
> if (pmc->perf_event)
> @@ -303,15 +322,18 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
>
> entry = kvm_find_cpuid_entry(vcpu, 0xa, 0);
> if (!entry)
> - return;
> + goto end;
> eax.full = entry->eax;
> edx.full = entry->edx;
>
> pmu->version = eax.split.version_id;
> if (!pmu->version)
> - return;
> + goto end;
>
> perf_get_x86_pmu_capability(&x86_pmu);
> + pmu->perf_capabilities = vmx_supported_perf_capabilities();
> + if (!pmu->perf_capabilities)
> + guest_cpuid_clear(vcpu, X86_FEATURE_PDCM);
>
> pmu->nr_arch_gp_counters = min_t(int, eax.split.num_counters,
> x86_pmu.num_counters_gp);
> @@ -351,6 +373,10 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
> INTEL_PMC_MAX_GENERIC, pmu->nr_arch_fixed_counters);
>
> nested_vmx_pmu_entry_exit_ctls_update(vcpu);
> + return;
> +
> +end:
> + guest_cpuid_clear(vcpu, X86_FEATURE_PDCM);
> }
>
> static void intel_pmu_init(struct kvm_vcpu *vcpu)
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 4f844257a72d..abc0f15a4de5 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7112,6 +7112,8 @@ static __init void vmx_set_cpu_caps(void)
> kvm_cpu_cap_check_and_set(X86_FEATURE_INVPCID);
> if (vmx_pt_mode_is_host_guest())
> kvm_cpu_cap_check_and_set(X86_FEATURE_INTEL_PT);
> + if (vmx_supported_perf_capabilities())
> + kvm_cpu_cap_check_and_set(X86_FEATURE_PDCM);
>
> /* PKU is not yet implemented for shadow paging. */
> if (enable_ept && boot_cpu_has(X86_FEATURE_OSPKE))
>
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