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 KVM_HINTS_REALTIME, Because
that hint guarantees we have a 1:1 vCPU:CPU binding and guaranteed
no over-commit.
And a per-VM capability is added to configure aperfmperf mode
Signed-off-by: Li RongQing <[email protected]>
Signed-off-by: Chai Wen <[email protected]>
Signed-off-by: Jia Lina <[email protected]>
---
diff v5:
return error if guest is configured with mperf/aperf, but host cpu has not
diff v4:
fix maybe-uninitialized warning
diff v3:
fix interception of MSR_IA32_MPERF/APERF in svm
diff v2:
support aperfmperf pass though
move common codes to kvm_get_msr_common
diff v1:
1. support AMD, but not test
2. support per-vm capability to enable
Documentation/virt/kvm/api.rst | 10 ++++++++++
arch/x86/include/asm/kvm_host.h | 11 +++++++++++
arch/x86/kvm/cpuid.c | 15 ++++++++++++++-
arch/x86/kvm/svm/svm.c | 8 ++++++++
arch/x86/kvm/vmx/vmx.c | 6 ++++++
arch/x86/kvm/x86.c | 42 +++++++++++++++++++++++++++++++++++++++++
arch/x86/kvm/x86.h | 15 +++++++++++++++
include/uapi/linux/kvm.h | 1 +
8 files changed, 107 insertions(+), 1 deletion(-)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index d871dacb984e..f854f4da6fd8 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6126,3 +6126,13 @@ 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, 1 for software emulation, 2 for pass-through
+:Returns: 0 on success; -1 on error
+
+This capability indicates that KVM supports APERF and MPERF MSR registers
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index fd78bd44b2d6..14643f8af9c4 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -824,6 +824,9 @@ struct kvm_vcpu_arch {
/* AMD MSRC001_0015 Hardware Configuration */
u64 msr_hwcr;
+
+ u64 v_mperf;
+ u64 v_aperf;
};
struct kvm_lpage_info {
@@ -889,6 +892,12 @@ 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
@@ -986,6 +995,8 @@ 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/cpuid.c b/arch/x86/kvm/cpuid.c
index cd708b0b460a..80f18b29a845 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -122,6 +122,16 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
MSR_IA32_MISC_ENABLE_MWAIT);
}
+ best = kvm_find_cpuid_entry(vcpu, 6, 0);
+ if (best) {
+ if (guest_has_aperfmperf(vcpu->kvm)) {
+ if (!boot_cpu_has(X86_FEATURE_APERFMPERF))
+ return -EINVAL;
+ best->ecx |= 1;
+ } else {
+ best->ecx &= ~1;
+ }
+ }
/* Note, maxphyaddr must be updated before tdp_level. */
vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
vcpu->arch.tdp_level = kvm_x86_ops.get_tdp_level(vcpu);
@@ -557,7 +567,10 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
case 6: /* Thermal management */
entry->eax = 0x4; /* allow ARAT */
entry->ebx = 0;
- entry->ecx = 0;
+ if (boot_cpu_has(X86_FEATURE_APERFMPERF))
+ entry->ecx = 0x1;
+ else
+ entry->ecx = 0x0;
entry->edx = 0;
break;
/* function 7 has additional index. */
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index e9c0fb68387d..1d38fe3afc0d 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1200,6 +1200,14 @@ 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 0ea5a225a579..18d02e95db04 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6916,6 +6916,12 @@ 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);
+ }
+
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 8ac69c16f153..de6406d51722 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3271,6 +3271,12 @@ 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:
+ 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->index, &msr_info->data);
@@ -3480,6 +3486,9 @@ 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;
}
@@ -4930,6 +4939,11 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
kvm->arch.exception_payload_enabled = cap->args[0];
r = 0;
break;
+ case KVM_CAP_APERFMPERF:
+ kvm->arch.aperfmperf_mode =
+ boot_cpu_has(X86_FEATURE_APERFMPERF) ? cap->args[0] : 0;
+ r = 0;
+ break;
default:
r = -EINVAL;
break;
@@ -8217,6 +8231,25 @@ 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)
+{
+ 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
@@ -8230,6 +8263,8 @@ 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)) {
@@ -8393,6 +8428,9 @@ 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);
/*
@@ -8514,6 +8552,10 @@ 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 ac9eba0289d1..57285a53078d 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1018,6 +1018,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_S390_PROTECTED 180
#define KVM_CAP_PPC_SECURE_GUEST 181
#define KVM_CAP_HALT_POLL 182
+#define KVM_CAP_APERFMPERF 183
#ifdef KVM_CAP_IRQ_ROUTING
--
2.16.2
Hi RongQing,
On 2020/6/5 9:44, 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
s/None/Note
>
> Software emulation: the period of aperf/mperf in guest mode are
> accumulated as emulated value
>
> Pass-though: it is only suitable for KVM_HINTS_REALTIME, Because
> that hint guarantees we have a 1:1 vCPU:CPU binding and guaranteed
> no over-commit.
The flag "KVM_HINTS_REALTIME 0" (in the Documentation/virt/kvm/cpuid.rst)
is claimed as "guest checks this feature bit to determine that vCPUs are never
preempted for an unlimited time allowing optimizations".
I couldn't see its relationship with "1:1 vCPU: pCPU binding".
The patch doesn't check this flag as well for your pass-through purpose.
Thanks,
Like Xu
>
> And a per-VM capability is added to configure aperfmperf mode
>
> Signed-off-by: Li RongQing <[email protected]>
> Signed-off-by: Chai Wen <[email protected]>
> Signed-off-by: Jia Lina <[email protected]>
> ---
> diff v5:
> return error if guest is configured with mperf/aperf, but host cpu has not
>
> diff v4:
> fix maybe-uninitialized warning
>
> diff v3:
> fix interception of MSR_IA32_MPERF/APERF in svm
>
> diff v2:
> support aperfmperf pass though
> move common codes to kvm_get_msr_common
>
> diff v1:
> 1. support AMD, but not test
> 2. support per-vm capability to enable
>
>
> Documentation/virt/kvm/api.rst | 10 ++++++++++
> arch/x86/include/asm/kvm_host.h | 11 +++++++++++
> arch/x86/kvm/cpuid.c | 15 ++++++++++++++-
> arch/x86/kvm/svm/svm.c | 8 ++++++++
> arch/x86/kvm/vmx/vmx.c | 6 ++++++
> arch/x86/kvm/x86.c | 42 +++++++++++++++++++++++++++++++++++++++++
> arch/x86/kvm/x86.h | 15 +++++++++++++++
> include/uapi/linux/kvm.h | 1 +
> 8 files changed, 107 insertions(+), 1 deletion(-)
> -----邮件原件-----
> 发件人: Xu, Like [mailto:[email protected]]
> 发送时间: 2020年6月5日 10:32
> 收件人: Li,Rongqing <[email protected]>
> 抄送: [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]
> 主题: Re: [PATCH][v6] KVM: X86: support APERF/MPERF registers
>
> Hi RongQing,
>
> On 2020/6/5 9:44, 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
> s/None/Note
> >
> > Software emulation: the period of aperf/mperf in guest mode are
> > accumulated as emulated value
> >
> > Pass-though: it is only suitable for KVM_HINTS_REALTIME, Because that
> > hint guarantees we have a 1:1 vCPU:CPU binding and guaranteed no
> > over-commit.
> The flag "KVM_HINTS_REALTIME 0" (in the Documentation/virt/kvm/cpuid.rst)
> is claimed as "guest checks this feature bit to determine that vCPUs are never
> preempted for an unlimited time allowing optimizations".
>
> I couldn't see its relationship with "1:1 vCPU: pCPU binding".
> The patch doesn't check this flag as well for your pass-through purpose.
>
> Thanks,
> Like Xu
I think this is user space jobs to bind HINT_REALTIME and mperf passthrough, KVM just do what userspace wants.
and this gives user space a possibility, guest has passthrough mperfaperf without HINT_REALTIME, guest can get coarse cpu frequency without performance effect if guest can endure error frequency occasionally
-Li
On 6/5/2020 9:44 AM, 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 KVM_HINTS_REALTIME, Because
> that hint guarantees we have a 1:1 vCPU:CPU binding and guaranteed
> no over-commit.
>
> And a per-VM capability is added to configure aperfmperf mode
>
> Signed-off-by: Li RongQing <[email protected]>
> Signed-off-by: Chai Wen <[email protected]>
> Signed-off-by: Jia Lina <[email protected]>
> ---
> diff v5:
> return error if guest is configured with mperf/aperf, but host cpu has not
>
> diff v4:
> fix maybe-uninitialized warning
>
> diff v3:
> fix interception of MSR_IA32_MPERF/APERF in svm
>
> diff v2:
> support aperfmperf pass though
> move common codes to kvm_get_msr_common
>
> diff v1:
> 1. support AMD, but not test
> 2. support per-vm capability to enable
>
>
> Documentation/virt/kvm/api.rst | 10 ++++++++++
> arch/x86/include/asm/kvm_host.h | 11 +++++++++++
> arch/x86/kvm/cpuid.c | 15 ++++++++++++++-
> arch/x86/kvm/svm/svm.c | 8 ++++++++
> arch/x86/kvm/vmx/vmx.c | 6 ++++++
> arch/x86/kvm/x86.c | 42 +++++++++++++++++++++++++++++++++++++++++
> arch/x86/kvm/x86.h | 15 +++++++++++++++
> include/uapi/linux/kvm.h | 1 +
> 8 files changed, 107 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index d871dacb984e..f854f4da6fd8 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -6126,3 +6126,13 @@ 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, 1 for software emulation, 2 for pass-through
> +:Returns: 0 on success; -1 on error
> +
> +This capability indicates that KVM supports APERF and MPERF MSR registers
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index fd78bd44b2d6..14643f8af9c4 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -824,6 +824,9 @@ struct kvm_vcpu_arch {
>
> /* AMD MSRC001_0015 Hardware Configuration */
> u64 msr_hwcr;
> +
> + u64 v_mperf;
> + u64 v_aperf;
> };
>
> struct kvm_lpage_info {
> @@ -889,6 +892,12 @@ 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
> @@ -986,6 +995,8 @@ 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/cpuid.c b/arch/x86/kvm/cpuid.c
> index cd708b0b460a..80f18b29a845 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -122,6 +122,16 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
> MSR_IA32_MISC_ENABLE_MWAIT);
> }
>
> + best = kvm_find_cpuid_entry(vcpu, 6, 0);
> + if (best) {
> + if (guest_has_aperfmperf(vcpu->kvm)) {
> + if (!boot_cpu_has(X86_FEATURE_APERFMPERF))
> + return -EINVAL;
kvm_vm_ioctl_enable_cap() ensures that guest_has_aperfmperf() always
aligns with boot_cpu_has(X86_FEATURE_APERFMPERF). So above is unnecessary.
> + best->ecx |= 1;
> + } else {
> + best->ecx &= ~1;
> + }
> + }
you could do
bool guest_cpuid_aperfmperf = false;
if (best)
guest_cpuid_aperfmperf = !!(best->ecx & BIT(0));
if (guest_cpuid_aperfmerf != guest_has_aperfmperf(vcpu->kvm))
return -EINVAL;
In fact, I think we can do nothing here. Leave it as what usersapce
wants just like how KVM treats other CPUID bits.
Paolo,
What's your point?
> /* Note, maxphyaddr must be updated before tdp_level. */
> vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
> vcpu->arch.tdp_level = kvm_x86_ops.get_tdp_level(vcpu);
[...]
> @@ -4930,6 +4939,11 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
> kvm->arch.exception_payload_enabled = cap->args[0];
> r = 0;
> break;
> + case KVM_CAP_APERFMPERF:
> + kvm->arch.aperfmperf_mode =
> + boot_cpu_has(X86_FEATURE_APERFMPERF) ? cap->args[0] : 0;
Shouldn't check whether cap->args[0] is a valid value?
> + r = 0;
> + break;
> default:
> r = -EINVAL;
> break;
On 2020/6/5 12:23, Li,Rongqing wrote:
>
>
>> -----邮件原件-----
>> 发件人: Xu, Like [mailto:[email protected]]
>> 发送时间: 2020年6月5日 10:32
>> 收件人: Li,Rongqing <[email protected]>
>> 抄送: [email protected]; [email protected]; [email protected];
>> [email protected]; [email protected]; [email protected]; [email protected];
>> [email protected]; [email protected]; [email protected];
>> [email protected]; [email protected]; [email protected];
>> [email protected]
>> 主题: Re: [PATCH][v6] KVM: X86: support APERF/MPERF registers
>>
>> Hi RongQing,
>>
>> On 2020/6/5 9:44, 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
>> s/None/Note
>>>
>>> Software emulation: the period of aperf/mperf in guest mode are
>>> accumulated as emulated value
>>>
>>> Pass-though: it is only suitable for KVM_HINTS_REALTIME, Because that
>>> hint guarantees we have a 1:1 vCPU:CPU binding and guaranteed no
>>> over-commit.
>> The flag "KVM_HINTS_REALTIME 0" (in the Documentation/virt/kvm/cpuid.rst)
>> is claimed as "guest checks this feature bit to determine that vCPUs are never
>> preempted for an unlimited time allowing optimizations".
>>
>> I couldn't see its relationship with "1:1 vCPU: pCPU binding".
>> The patch doesn't check this flag as well for your pass-through purpose.
>>
>> Thanks,
>> Like Xu
>
>
> I think this is user space jobs to bind HINT_REALTIME and mperf passthrough, KVM just do what userspace wants.
>
That's fine for user space to bind HINT_REALTIME and mperf passthrough，
But I was asking why HINT_REALTIME means "1:1 vCPU: pCPU binding".
As you said, "Pass-though: it is only suitable for KVM_HINTS_REALTIME",
which means, KVM needs to make sure the kvm->arch.aperfmperf_mode value
could "only" be set to KVM_APERFMPERF_PT when the check
kvm_para_has_hint(KVM_HINTS_REALTIME) is passed.
Specifically, the KVM_HINTS_REALTIME is a per-kvm capability
while the kvm_aperfmperf_mode is a per-vm capability. It's unresolved.
KVM doesn't always do what userspace wants especially
you're trying to expose some features about
power and thermal management in the virtualization context.
> and this gives user space a possibility, guest has passthrough mperfaperf without HINT_REALTIME, guest can get coarse cpu frequency without performance effect if guest can endure error frequency occasionally
>
>
> -Li
>
On 05/06/20 07:00, Xiaoyao Li wrote:
> you could do
>
> bool guest_cpuid_aperfmperf = false;
> if (best)
> guest_cpuid_aperfmperf = !!(best->ecx & BIT(0));
>
> if (guest_cpuid_aperfmerf != guest_has_aperfmperf(vcpu->kvm))
> return -EINVAL;
>
>
> In fact, I think we can do nothing here. Leave it as what usersapce
> wants just like how KVM treats other CPUID bits.
The reason to do it like Rongqing did is that it's suggested to take the
output of KVM_GET_SUPPORTED_CPUID and pass it down to KVM_SET_CPUID2.
Unfortunately we have KVM_GET_SUPPORTED_CPUID as a /dev/kvm (not VM)
ioctl, otherwise you could have used guest_has_aperfmperf to affect the
output of KVM_GET_SUPPORTED_CPUID.
I think it's okay however to keep it simple as you suggest. In this
case however __do_cpuid_func must not return the X86_FEATURE_APERFMPERF bit.
The guest can instead check for the availability of KVM_CAP_APERFMPERF,
which is already done in Rongqing's patch.
>> @@ -4930,6 +4939,11 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
>> kvm->arch.exception_payload_enabled = cap->args[0];
>> r = 0;
>> break;
>> + case KVM_CAP_APERFMPERF:
>> + kvm->arch.aperfmperf_mode =
>> + boot_cpu_has(X86_FEATURE_APERFMPERF) ? cap->args[0] : 0;
>
> Shouldn't check whether cap->args[0] is a valid value?
Yes, only valid values should be allowed.
Also, it should fail with -EINVAL if the host does not have
X86_FEATURE_APERFMPERF.
Thanks,
Paolo
> -----邮件原件-----
> 发件人: Like Xu [mailto:[email protected]]
> 发送时间: 2020年6月5日 13:29
> 收件人: Li,Rongqing <[email protected]>; [email protected]
> 抄送: [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]
> 主题: Re: 答复: [PATCH][v6] KVM: X86: support APERF/MPERF registers
>
> On 2020/6/5 12:23, Li,Rongqing wrote:
> >
> >
> >> -----邮件原件-----
> >> 发件人: Xu, Like [mailto:[email protected]]
> >> 发送时间: 2020年6月5日 10:32
> >> 收件人: Li,Rongqing <[email protected]>
> >> 抄送: [email protected]; [email protected];
> >> [email protected]; [email protected]; [email protected]; [email protected];
> >> [email protected]; [email protected]; [email protected];
> >> [email protected]; [email protected];
> >> [email protected]; [email protected]; [email protected]
> >> 主题: Re: [PATCH][v6] KVM: X86: support APERF/MPERF registers
> >>
> >> Hi RongQing,
> >>
> >> On 2020/6/5 9:44, 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
> >> s/None/Note
> >>>
> >>> Software emulation: the period of aperf/mperf in guest mode are
> >>> accumulated as emulated value
> >>>
> >>> Pass-though: it is only suitable for KVM_HINTS_REALTIME, Because
> >>> that hint guarantees we have a 1:1 vCPU:CPU binding and guaranteed
> >>> no over-commit.
> >> The flag "KVM_HINTS_REALTIME 0" (in the
> >> Documentation/virt/kvm/cpuid.rst) is claimed as "guest checks this
> >> feature bit to determine that vCPUs are never preempted for an unlimited
> time allowing optimizations".
> >>
> >> I couldn't see its relationship with "1:1 vCPU: pCPU binding".
> >> The patch doesn't check this flag as well for your pass-through purpose.
> >>
> >> Thanks,
> >> Like Xu
> >
> >
> > I think this is user space jobs to bind HINT_REALTIME and mperf passthrough,
> KVM just do what userspace wants.
> >
>
> That's fine for user space to bind HINT_REALTIME and mperf passthrough，
> But I was asking why HINT_REALTIME means "1:1 vCPU: pCPU binding".
>
> As you said, "Pass-though: it is only suitable for KVM_HINTS_REALTIME", which
> means, KVM needs to make sure the kvm->arch.aperfmperf_mode value could
> "only" be set to KVM_APERFMPERF_PT when the check
> kvm_para_has_hint(KVM_HINTS_REALTIME) is passed.
>
pining vcpu can ensure that guest get correct mperf/aperf, but a user
has the choice to not pin, at that condition, do not think it is bug, this wants to say
> Specifically, the KVM_HINTS_REALTIME is a per-kvm capability while the
> kvm_aperfmperf_mode is a per-vm capability. It's unresolved.
>
Do you have any solution?
-Rongqing
> KVM doesn't always do what userspace wants especially you're trying to
> expose some features about power and thermal management in the
> virtualization context.
>
> > and this gives user space a possibility, guest has passthrough
> > mperfaperf without HINT_REALTIME, guest can get coarse cpu frequency
> > without performance effect if guest can endure error frequency
> > occasionally
> >
>
>
> >
> > -Li
> >
On 05/06/20 11:41, Li,Rongqing wrote:
>>
>> As you said, "Pass-though: it is only suitable for KVM_HINTS_REALTIME", which
>> means, KVM needs to make sure the kvm->arch.aperfmperf_mode value could
>> "only" be set to KVM_APERFMPERF_PT when the check
>> kvm_para_has_hint(KVM_HINTS_REALTIME) is passed.
>>
> pining vcpu can ensure that guest get correct mperf/aperf, but a user
> has the choice to not pin, at that condition, do not think it is bug, this wants to say
Also, userspace can also pin without exposing KVM_HINTS_REALTIME. So
it's better not to check.
Paolo
On Thu, Jun 4, 2020 at 11:35 PM Paolo Bonzini <[email protected]> wrote:
>
> On 05/06/20 07:00, Xiaoyao Li wrote:
> > you could do
> >
> > bool guest_cpuid_aperfmperf = false;
> > if (best)
> > guest_cpuid_aperfmperf = !!(best->ecx & BIT(0));
> >
> > if (guest_cpuid_aperfmerf != guest_has_aperfmperf(vcpu->kvm))
> > return -EINVAL;
> >
> >
> > In fact, I think we can do nothing here. Leave it as what usersapce
> > wants just like how KVM treats other CPUID bits.
>
> The reason to do it like Rongqing did is that it's suggested to take the
> output of KVM_GET_SUPPORTED_CPUID and pass it down to KVM_SET_CPUID2.
> Unfortunately we have KVM_GET_SUPPORTED_CPUID as a /dev/kvm (not VM)
> ioctl, otherwise you could have used guest_has_aperfmperf to affect the
> output of KVM_GET_SUPPORTED_CPUID.
>
> I think it's okay however to keep it simple as you suggest. In this
> case however __do_cpuid_func must not return the X86_FEATURE_APERFMPERF bit.
>
> The guest can instead check for the availability of KVM_CAP_APERFMPERF,
> which is already done in Rongqing's patch.
>
> >> @@ -4930,6 +4939,11 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
> >> kvm->arch.exception_payload_enabled = cap->args[0];
> >> r = 0;
> >> break;
> >> + case KVM_CAP_APERFMPERF:
> >> + kvm->arch.aperfmperf_mode =
> >> + boot_cpu_has(X86_FEATURE_APERFMPERF) ? cap->args[0] : 0;
> >
> > Shouldn't check whether cap->args[0] is a valid value?
>
> Yes, only valid values should be allowed.
>
> Also, it should fail with -EINVAL if the host does not have
> X86_FEATURE_APERFMPERF.
Should enabling/disabling this capability be disallowed once vCPUs
have been created?
On 05/06/20 19:16, Jim Mattson wrote:
>>>> @@ -4930,6 +4939,11 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
>>>> kvm->arch.exception_payload_enabled = cap->args[0];
>>>> r = 0;
>>>> break;
>>>> + case KVM_CAP_APERFMPERF:
>>>> + kvm->arch.aperfmperf_mode =
>>>> + boot_cpu_has(X86_FEATURE_APERFMPERF) ? cap->args[0] : 0;
>>> Shouldn't check whether cap->args[0] is a valid value?
>> Yes, only valid values should be allowed.
>>
>> Also, it should fail with -EINVAL if the host does not have
>> X86_FEATURE_APERFMPERF.
> Should enabling/disabling this capability be disallowed once vCPUs
> have been created?
>
That's a good idea, yes.
Paolo
> -----邮件原件-----
> 发件人: Paolo Bonzini [mailto:[email protected]]
> 发送时间: 2020年6月6日 1:22
> 收件人: Jim Mattson <[email protected]>
> 抄送: Xiaoyao Li <[email protected]>; Li,Rongqing <[email protected]>;
> LKML <[email protected]>; kvm list <[email protected]>; the
> arch/x86 maintainers <[email protected]>; H . Peter Anvin <[email protected]>;
> Borislav Petkov <[email protected]>; Ingo Molnar <[email protected]>; Thomas
> Gleixner <[email protected]>; Wanpeng Li <[email protected]>; Vitaly
> Kuznetsov <[email protected]>; Sean Christopherson
> <[email protected]>; [email protected]
> 主题: Re: [PATCH][v6] KVM: X86: support APERF/MPERF registers
>
> On 05/06/20 19:16, Jim Mattson wrote:
> >>>> @@ -4930,6 +4939,11 @@ int kvm_vm_ioctl_enable_cap(struct kvm
> *kvm,
> >>>> kvm->arch.exception_payload_enabled = cap->args[0];
> >>>> r = 0;
> >>>> break;
> >>>> + case KVM_CAP_APERFMPERF:
> >>>> + kvm->arch.aperfmperf_mode =
> >>>> + boot_cpu_has(X86_FEATURE_APERFMPERF) ?
> cap->args[0] :
> >>>> + 0;
> >>> Shouldn't check whether cap->args[0] is a valid value?
> >> Yes, only valid values should be allowed.
> >>
> >> Also, it should fail with -EINVAL if the host does not have
> >> X86_FEATURE_APERFMPERF.
> > Should enabling/disabling this capability be disallowed once vCPUs
> > have been created?
> >
>
> That's a good idea, yes.
>
> Paolo
Thank you all, I will send a new version
-Li