Re: [PATCH][v7] KVM: X86: support APERF/MPERF registers

From: Xu, Like
Date: Mon Jun 08 2020 - 08:41:43 EST

Next message: Michael S. Tsirkin: "[PATCH] vhost/test: fix up after API change"
Previous message: Paolo Bonzini: "Re: [PATCH kvm-unit-tests 1/2] svm: Add ability to execute test via test_run on a vcpu other than vcpu 0"
In reply to: Li RongQing: "[PATCH][v7] KVM: X86: support APERF/MPERF registers"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

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@xxxxxxxxx>
Signed-off-by: Chai Wen <chaiwen@xxxxxxxxx>
Signed-off-by: Jia Lina <jialina01@xxxxxxxxx>
---
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

Next message: Michael S. Tsirkin: "[PATCH] vhost/test: fix up after API change"
Previous message: Paolo Bonzini: "Re: [PATCH kvm-unit-tests 1/2] svm: Add ability to execute test via test_run on a vcpu other than vcpu 0"
In reply to: Li RongQing: "[PATCH][v7] KVM: X86: support APERF/MPERF registers"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]