Date:   Mon, 8 Jun 2020 20:41:35 +0800
From:   "Xu, Like" <like.xu@...el.com>
To:     Li RongQing <lirongqing@...du.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org, x86@...nel.org,
        hpa@...or.com, bp@...en8.de, mingo@...hat.com, tglx@...utronix.de,
        jmattson@...gle.com, wanpengli@...cent.com, vkuznets@...hat.com,
        sean.j.christopherson@...el.com, pbonzini@...hat.com,
        xiaoyao.li@...el.com, wei.huang2@....com
Subject: Re: [PATCH][v7] KVM: X86: support APERF/MPERF registers

Hi RongQing,

On 2020/6/8 17:34, Li RongQing wrote:
> Guest kernel reports a fixed cpu frequency in /proc/cpuinfo,
> this is confused to user when turbo is enable, and aperf/mperf
> can be used to show current cpu frequency after 7d5905dc14a
> "(x86 / CPU: Always show current CPU frequency in /proc/cpuinfo)"
> so guest should support aperf/mperf capability
>
> This patch implements aperf/mperf by three mode: none, software
> emulation, and pass-through
>
> None: default mode, guest does not support aperf/mperf
>
> Software emulation: the period of aperf/mperf in guest mode are
> accumulated as emulated value
>
> Pass-though: it is only suitable for pinned vcpu
I know the "pass-though" idea comes from PeterZ.

 From the guest point of view,
it would be inaccurate if guest/host share the
TSC Frequency clock counters in the pass-through mode
due to the cost from KVM part even in the vcpu pinned mode.

The "software emulation" mode should be enough for your case.
>
> And a per-VM capability is added to configure aperfmperf mode
>
> Signed-off-by: Li RongQing <lirongqing@...du.com>
> Signed-off-by: Chai Wen <chaiwen@...du.com>
> Signed-off-by: Jia Lina <jialina01@...du.com>
> ---
> diff v6:
> drop the unneed check from kvm_update_cpuid and __do_cpuid_func
> add the validation check in kvm_vm_ioctl_enable_cap
> thank for Jim Mattson,  Paolo Bonzini and Xiaoyao Li
>
> diff v5:
> return error if guest is configured with aperf/mperf, but host cpu has not
>
> diff v4:
> fix maybe-uninitialized warning
>
> diff v3:
> fix interception of MSR_IA32_APERF/MPERF in svm
> thanks for wei.huang2
>
> diff v2:
> support aperfmperf pass though
> move common codes to kvm_get_msr_common
> thanks for Xiaoyao Li and Peter Zijlstra
>
> diff v1:
> 1. support AMD, but not test
> 2. support per-vm capability to enable
> Documentation/virt/kvm/api.rst  | 16 ++++++++++++
>   arch/x86/include/asm/kvm_host.h | 11 ++++++++
>   arch/x86/kvm/svm/svm.c          |  8 ++++++
>   arch/x86/kvm/vmx/vmx.c          |  6 +++++
>   arch/x86/kvm/x86.c              | 56 +++++++++++++++++++++++++++++++++++++++++
>   arch/x86/kvm/x86.h              | 15 +++++++++++
>   include/uapi/linux/kvm.h        |  1 +
>   7 files changed, 113 insertions(+)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 426f94582b7a..ae30ac02a771 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -6150,3 +6150,19 @@ KVM can therefore start protected VMs.
>   This capability governs the KVM_S390_PV_COMMAND ioctl and the
>   KVM_MP_STATE_LOAD MP_STATE. KVM_SET_MP_STATE can fail for protected
>   guests when the state change is invalid.
> +
> +8.23 KVM_CAP_APERFMPERF
> +----------------------------
> +
> +:Architectures: x86
> +:Parameters: args[0] is aperfmperf mode;
> +             0 for not support, it is default mode
> +             1 for software emulation
> +             2 for pass-through which is only suitable for pinned vcpu
> +:Returns: 0 on success, -EINVAL when args[0] contains invalid,
> +           -EBUSY if vcpus has been created
> +
> +Enabling this capability on a VM provides guest with aperf/mperf
> +register, which are used to get cpu running frequency currently
> +
> +Do not enable KVM_CAP_APERFMPERF if host does not support aperf/mperf
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 1da5858501ca..7d1d3668c4f1 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -829,6 +829,9 @@ struct kvm_vcpu_arch {
>   
>   	/* AMD MSRC001_0015 Hardware Configuration */
>   	u64 msr_hwcr;
> +
> +	u64 v_mperf;
> +	u64 v_aperf;
>   };
>   
>   struct kvm_lpage_info {
> @@ -907,6 +910,12 @@ enum kvm_irqchip_mode {
>   	KVM_IRQCHIP_SPLIT,        /* created with KVM_CAP_SPLIT_IRQCHIP */
>   };
>   
> +enum kvm_aperfmperf_mode {
> +	KVM_APERFMPERF_NONE,
> +	KVM_APERFMPERF_SOFT,      /* software emulate aperfmperf */
> +	KVM_APERFMPERF_PT,        /* pass-through aperfmperf to guest */
> +};
> +
>   #define APICV_INHIBIT_REASON_DISABLE    0
>   #define APICV_INHIBIT_REASON_HYPERV     1
>   #define APICV_INHIBIT_REASON_NESTED     2
> @@ -1004,6 +1013,8 @@ struct kvm_arch {
>   
>   	struct kvm_pmu_event_filter *pmu_event_filter;
>   	struct task_struct *nx_lpage_recovery_thread;
> +
> +	enum kvm_aperfmperf_mode aperfmperf_mode;
>   };
>   
>   struct kvm_vm_stat {
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 9e333b91ff78..0db7d866e09f 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -1198,6 +1198,14 @@ static int svm_create_vcpu(struct kvm_vcpu *vcpu)
>   	svm->msrpm = page_address(msrpm_pages);
>   	svm_vcpu_init_msrpm(svm->msrpm);
>   
> +	if (guest_aperfmperf_soft(vcpu->kvm)) {
> +		set_msr_interception(svm->msrpm, MSR_IA32_MPERF, 0, 0);
> +		set_msr_interception(svm->msrpm, MSR_IA32_APERF, 0, 0);
> +	} else if (guest_aperfmperf_pt(vcpu->kvm)) {
> +		set_msr_interception(svm->msrpm, MSR_IA32_MPERF, 1, 0);
> +		set_msr_interception(svm->msrpm, MSR_IA32_APERF, 1, 0);
> +	}
> +
>   	svm->nested.msrpm = page_address(nested_msrpm_pages);
>   	svm_vcpu_init_msrpm(svm->nested.msrpm);
>   
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 170cc76a581f..952e3728ca86 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6914,6 +6914,12 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu)
>   		vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C6_RESIDENCY, MSR_TYPE_R);
>   		vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C7_RESIDENCY, MSR_TYPE_R);
>   	}
> +
> +	if (guest_aperfmperf_pt(vcpu->kvm)) {
> +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_MPERF, MSR_TYPE_R);
> +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_APERF, MSR_TYPE_R);
Both two registers are writable on the Intel platforms with the description 
of "R/Write to clear",
and you lost this part in the kvm_set_msr_common() for "software emulation" 
mode.
> +	}
> +
>   	vmx->msr_bitmap_mode = 0;
>   
>   	vmx->loaded_vmcs = &vmx->vmcs01;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 9e41b5135340..84884f4778cb 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3324,6 +3324,12 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   	case MSR_K7_HWCR:
>   		msr_info->data = vcpu->arch.msr_hwcr;
>   		break;
> +	case MSR_IA32_MPERF:
What if vcpu CPUID doesn't set CPUID.06H: ECX[0] ?
> +		msr_info->data = vcpu->arch.v_mperf;
> +		break;
> +	case MSR_IA32_APERF:
> +		msr_info->data = vcpu->arch.v_aperf;
> +		break;
>   	default:
>   		if (kvm_pmu_is_valid_msr(vcpu, msr_info->index))
>   			return kvm_pmu_get_msr(vcpu, msr_info);
> @@ -3534,6 +3540,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>   	case KVM_CAP_HYPERV_ENLIGHTENED_VMCS:
>   		r = kvm_x86_ops.nested_ops->enable_evmcs != NULL;
>   		break;
> +	case KVM_CAP_APERFMPERF:
> +		r = boot_cpu_has(X86_FEATURE_APERFMPERF) ? 1 : 0;
> +		break;
>   	default:
>   		break;
>   	}
> @@ -4985,6 +4994,25 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
>   		kvm->arch.exception_payload_enabled = cap->args[0];
>   		r = 0;
>   		break;
> +	case KVM_CAP_APERFMPERF:
If the pass-through mode could be dropped,
we may en/disable the APERF/MPERF via CPUID.06H: ECX[0].
> +		r = 0;
> +		mutex_lock(&kvm->lock);
> +		if (kvm->created_vcpus)
> +			r = -EBUSY;
> +		if (r)
> +			goto aperfmperf_unlock;
> +
> +		r = -EINVAL;
> +		if (cap->args[0] > KVM_APERFMPERF_PT)
> +			goto aperfmperf_unlock;
> +		if (cap->args[0] != KVM_APERFMPERF_NONE
> +				&& !boot_cpu_has(X86_FEATURE_APERFMPERF))
> +			goto aperfmperf_unlock;
> +		r = 0;
> +		kvm->arch.aperfmperf_mode = cap->args[0];
> +aperfmperf_unlock:
> +		mutex_unlock(&kvm->lock);
> +		break;
>   	default:
>   		r = -EINVAL;
>   		break;
> @@ -8311,6 +8339,25 @@ void __kvm_request_immediate_exit(struct kvm_vcpu *vcpu)
>   }
>   EXPORT_SYMBOL_GPL(__kvm_request_immediate_exit);
>   
> +
> +static void guest_enter_aperfmperf(u64 *mperf, u64 *aperf)
> +{
It's called when the KVM_APERFMPERF_SOFT is enabled,
so there may be a #GP if host doesn't support.

Thanks,
Like Xu
> +	rdmsrl(MSR_IA32_MPERF, *mperf);
> +	rdmsrl(MSR_IA32_APERF, *aperf);
> +}
> +
> +static void guest_exit_aperfmperf(struct kvm_vcpu *vcpu,
> +		u64 mperf, u64 aperf)
> +{
> +	u64 perf;
> +
> +	rdmsrl(MSR_IA32_MPERF, perf);
> +	vcpu->arch.v_mperf += perf - mperf;
> +
> +	rdmsrl(MSR_IA32_APERF, perf);
> +	vcpu->arch.v_aperf += perf - aperf;
> +}
> +
>   /*
>    * Returns 1 to let vcpu_run() continue the guest execution loop without
>    * exiting to the userspace.  Otherwise, the value will be returned to the
> @@ -8324,6 +8371,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>   		kvm_cpu_accept_dm_intr(vcpu);
>   	fastpath_t exit_fastpath;
>   
> +	bool enable_aperfmperf = guest_aperfmperf_soft(vcpu->kvm);
> +	u64 uninitialized_var(mperf), uninitialized_var(aperf);
>   	bool req_immediate_exit = false;
>   
>   	if (kvm_request_pending(vcpu)) {
> @@ -8462,6 +8511,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>   
>   	preempt_disable();
>   
> +	if (unlikely(enable_aperfmperf))
> +		guest_enter_aperfmperf(&mperf, &aperf);
> +
>   	kvm_x86_ops.prepare_guest_switch(vcpu);
>   
>   	/*
> @@ -8583,6 +8635,10 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>   	}
>   
>   	local_irq_enable();
> +
> +	if (unlikely(enable_aperfmperf))
> +		guest_exit_aperfmperf(vcpu, mperf, aperf);
> +
>   	preempt_enable();
>   
>   	vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index 6eb62e97e59f..8216f697c53c 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -361,6 +361,21 @@ static inline bool kvm_dr7_valid(u64 data)
>   	return !(data >> 32);
>   }
>   
> +static inline bool guest_has_aperfmperf(struct kvm *kvm)
> +{
> +	return kvm->arch.aperfmperf_mode != KVM_APERFMPERF_NONE;
> +}
> +
> +static inline bool guest_aperfmperf_soft(struct kvm *kvm)
> +{
> +	return kvm->arch.aperfmperf_mode == KVM_APERFMPERF_SOFT;
> +}
> +
> +static inline bool guest_aperfmperf_pt(struct kvm *kvm)
> +{
> +	return kvm->arch.aperfmperf_mode == KVM_APERFMPERF_PT;
> +}
> +
>   void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu);
>   void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu);
>   u64 kvm_spec_ctrl_valid_bits(struct kvm_vcpu *vcpu);
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 4fdf30316582..c240941d7821 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1031,6 +1031,7 @@ struct kvm_ppc_resize_hpt {
>   #define KVM_CAP_PPC_SECURE_GUEST 181
>   #define KVM_CAP_HALT_POLL 182
>   #define KVM_CAP_ASYNC_PF_INT 183
> +#define KVM_CAP_APERFMPERF 184
>   
>   #ifdef KVM_CAP_IRQ_ROUTING
>   

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