diff mbox series

[v2,7/8] KVM: PMU: support to save/restore the guest lbr stack on vCPU switching

Message ID 1536233456-12173-8-git-send-email-wei.w.wang@intel.com (mailing list archive)
State New, archived
Headers show
Series Guest LBR Enabling | expand

Commit Message

Wang, Wei W Sept. 6, 2018, 11:30 a.m. UTC 
From: Like Xu <like.xu@intel.com>

This patch adds support to KVM to save/restore the lbr stack on vCPU
context switching.

When the guest sets the ACTIVE bit of MSR_KVM_PV_LBR_CTRL, a perf event
is created on the host for the related vCPU. This perf event ensures the
LBR stack to be saved/restored when the vCPU thread is scheduled out/in.
The perf event is removed and freed when the guest clears the ACTIVE
bit.

Signed-off-by: Like Xu <like.xu@intel.com>
Signed-off-by: Wei Wang <wei.w.wang@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
---
 arch/x86/include/asm/kvm_host.h |  2 ++
 arch/x86/kvm/cpuid.c            |  3 +-
 arch/x86/kvm/pmu_intel.c        | 71 ++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 74 insertions(+), 2 deletions(-)

Comments

Jann Horn Sept. 7, 2018, 2:36 p.m. UTC | #1 
On Fri, Sep 7, 2018 at 4:28 PM Wei Wang <wei.w.wang@intel.com> wrote:
> This patch adds support to KVM to save/restore the lbr stack on vCPU
> context switching.
>
> When the guest sets the ACTIVE bit of MSR_KVM_PV_LBR_CTRL, a perf event
> is created on the host for the related vCPU. This perf event ensures the
> LBR stack to be saved/restored when the vCPU thread is scheduled out/in.
> The perf event is removed and freed when the guest clears the ACTIVE
> bit.
[...]
> +void guest_lbr_event_release(struct kvm_pmu *pmu)
> +{
> +       struct perf_event *event = pmu->guest_lbr_event;
> +
> +       if (unlikely(!pmu->guest_lbr_event)) {
> +               pr_err("%s: guest_lbr_event already freed\n", __func__);
> +               return;
> +       }
> +
> +       if (event) {
> +               event->pmu->stop(event, PERF_EF_UPDATE);
> +               perf_event_release_kernel(event);
> +       }
> +       pmu->guest_lbr_event = NULL;
> +}

Is there some guarantee that this method will be called when the vCPU
is torn down on guest exit?
Wang, Wei W Sept. 7, 2018, 3:21 p.m. UTC | #2 
On Friday, September 7, 2018 10:37 PM, Jann Horn wrote:
> On Fri, Sep 7, 2018 at 4:28 PM Wei Wang <wei.w.wang@intel.com> wrote:
> > This patch adds support to KVM to save/restore the lbr stack on vCPU
> > context switching.
> >
> > When the guest sets the ACTIVE bit of MSR_KVM_PV_LBR_CTRL, a perf
> > event is created on the host for the related vCPU. This perf event
> > ensures the LBR stack to be saved/restored when the vCPU thread is
> scheduled out/in.
> > The perf event is removed and freed when the guest clears the ACTIVE
> > bit.
> [...]
> > +void guest_lbr_event_release(struct kvm_pmu *pmu) {
> > +       struct perf_event *event = pmu->guest_lbr_event;
> > +
> > +       if (unlikely(!pmu->guest_lbr_event)) {
> > +               pr_err("%s: guest_lbr_event already freed\n", __func__);
> > +               return;
> > +       }
> > +
> > +       if (event) {
> > +               event->pmu->stop(event, PERF_EF_UPDATE);
> > +               perf_event_release_kernel(event);
> > +       }
> > +       pmu->guest_lbr_event = NULL;
> > +}
> 
> Is there some guarantee that this method will be called when the vCPU is
> torn down on guest exit?

Thanks for reminding us this corner case. We didn’t consider that in this version. I think we could add guest_lbr_event_release() to kvm_arch_vcpu_destroy()

Best,
Wei
Gonglei (Arei) Sept. 18, 2018, 12:58 a.m. UTC | #3 
> -----Original Message-----
> From: kvm-owner@vger.kernel.org [mailto:kvm-owner@vger.kernel.org] On
> Behalf Of Wei Wang
> Sent: Thursday, September 06, 2018 7:31 PM
> To: linux-kernel@vger.kernel.org; kvm@vger.kernel.org; pbonzini@redhat.com;
> ak@linux.intel.com
> Cc: kan.liang@intel.com; peterz@infradead.org; mingo@redhat.com;
> rkrcmar@redhat.com; like.xu@intel.com; wei.w.wang@intel.com
> Subject: [PATCH v2 7/8] KVM: PMU: support to save/restore the guest lbr stack
> on vCPU switching
> 
> From: Like Xu <like.xu@intel.com>
> 
> This patch adds support to KVM to save/restore the lbr stack on vCPU
> context switching.
> 
> When the guest sets the ACTIVE bit of MSR_KVM_PV_LBR_CTRL, a perf event
> is created on the host for the related vCPU. This perf event ensures the
> LBR stack to be saved/restored when the vCPU thread is scheduled out/in.
> The perf event is removed and freed when the guest clears the ACTIVE
> bit.
> 

What about live migration? Does LBR stack need to be saved on the source side and
restored on the dest side with the passthrough mode?

Thanks,
-Gonglei

> Signed-off-by: Like Xu <like.xu@intel.com>
> Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Andi Kleen <ak@linux.intel.com>
> ---
>  arch/x86/include/asm/kvm_host.h |  2 ++
>  arch/x86/kvm/cpuid.c            |  3 +-
>  arch/x86/kvm/pmu_intel.c        | 71
> ++++++++++++++++++++++++++++++++++++++++-
>  3 files changed, 74 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h
> b/arch/x86/include/asm/kvm_host.h
> index 5db5ba3..cfbe90f 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -432,6 +432,8 @@ struct kvm_pmu {
>  	struct kvm_pmc fixed_counters[INTEL_PMC_MAX_FIXED];
>  	struct irq_work irq_work;
>  	u64 reprogram_pmi;
> +	u64 kvm_pv_lbr_ctrl;
> +	struct perf_event *guest_lbr_event;
>  };
> 
>  struct kvm_pmu_ops;
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 3b8a57b..8550eee 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -622,7 +622,8 @@ static inline int __do_cpuid_ent(struct
> kvm_cpuid_entry2 *entry, u32 function,
>  			     (1 << KVM_FEATURE_PV_UNHALT) |
>  			     (1 << KVM_FEATURE_PV_TLB_FLUSH) |
>  			     (1 << KVM_FEATURE_ASYNC_PF_VMEXIT) |
> -			     (1 << KVM_FEATURE_PV_SEND_IPI);
> +			     (1 << KVM_FEATURE_PV_SEND_IPI) |
> +			     (1 << KVM_FEATURE_PV_LBR_CTRL);
> 
>  		if (sched_info_on())
>  			entry->eax |= (1 << KVM_FEATURE_STEAL_TIME);
> diff --git a/arch/x86/kvm/pmu_intel.c b/arch/x86/kvm/pmu_intel.c
> index 5ab4a36..27c028d 100644
> --- a/arch/x86/kvm/pmu_intel.c
> +++ b/arch/x86/kvm/pmu_intel.c
> @@ -67,6 +67,62 @@ static void global_ctrl_changed(struct kvm_pmu *pmu,
> u64 data)
>  		reprogram_counter(pmu, bit);
>  }
> 
> +static void guest_lbr_event_create(struct kvm_pmu *pmu)
> +{
> +	struct perf_event *event;
> +	struct perf_event_attr attr = {
> +		.type = PERF_TYPE_RAW,
> +		.size = sizeof(attr),
> +		.pinned = true,
> +		.exclude_host = true,
> +		.sample_type = PERF_SAMPLE_BRANCH_STACK,
> +		.branch_sample_type = PERF_SAMPLE_BRANCH_CALL_STACK |
> +				      PERF_SAMPLE_BRANCH_USER |
> +				      PERF_SAMPLE_BRANCH_KERNEL,
> +	};
> +
> +	if (unlikely(pmu->guest_lbr_event)) {
> +		pr_err("%s: guest_lbr_event already created\n", __func__);
> +		return;
> +	}
> +
> +	event = perf_event_create_kernel_counter(&attr, -1, current, NULL,
> +						 NULL);
> +	if (IS_ERR(event)) {
> +		pr_err("%s: failed %ld\n", __func__, PTR_ERR(event));
> +		return;
> +	}
> +	pmu->guest_lbr_event = event;
> +}
> +
> +void guest_lbr_event_release(struct kvm_pmu *pmu)
> +{
> +	struct perf_event *event = pmu->guest_lbr_event;
> +
> +	if (unlikely(!pmu->guest_lbr_event)) {
> +		pr_err("%s: guest_lbr_event already freed\n", __func__);
> +		return;
> +	}
> +
> +	if (event) {
> +		event->pmu->stop(event, PERF_EF_UPDATE);
> +		perf_event_release_kernel(event);
> +	}
> +	pmu->guest_lbr_event = NULL;
> +}
> +
> +static void kvm_pv_lbr_ctrl_changed(struct kvm_pmu *pmu, u64 data)
> +{
> +	bool guest_lbr_active = data & KVM_PV_LBR_CTRL_ACTIVE;
> +
> +	if (guest_lbr_active)
> +		guest_lbr_event_create(pmu);
> +	else
> +		guest_lbr_event_release(pmu);
> +
> +	pmu->kvm_pv_lbr_ctrl = data;
> +}
> +
>  static unsigned intel_find_arch_event(struct kvm_pmu *pmu,
>  				      u8 event_select,
>  				      u8 unit_mask)
> @@ -145,7 +201,7 @@ static struct kvm_pmc *intel_msr_idx_to_pmc(struct
> kvm_vcpu *vcpu,
>  static bool intel_is_valid_msr(struct kvm_vcpu *vcpu, u32 msr)
>  {
>  	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
> -	int ret;
> +	int ret = 0;
> 
>  	switch (msr) {
>  	case MSR_CORE_PERF_FIXED_CTR_CTRL:
> @@ -154,6 +210,10 @@ 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_KVM_PV_LBR_CTRL:
> +		if (vcpu->kvm->arch.guest_lbr)
> +			ret = 1;
> +		break;
>  	default:
>  		ret = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0) ||
>  			get_gp_pmc(pmu, msr, MSR_P6_EVNTSEL0) ||
> @@ -182,6 +242,9 @@ 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_KVM_PV_LBR_CTRL:
> +		*data = pmu->kvm_pv_lbr_ctrl;
> +		return 0;
>  	default:
>  		if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0)) ||
>  		    (pmc = get_fixed_pmc(pmu, msr))) {
> @@ -234,6 +297,11 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu,
> struct msr_data *msr_info)
>  			return 0;
>  		}
>  		break;
> +	case MSR_KVM_PV_LBR_CTRL:
> +		if (pmu->kvm_pv_lbr_ctrl == data)
> +			return 0;
> +		kvm_pv_lbr_ctrl_changed(pmu, data);
> +		return 0;
>  	default:
>  		if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0)) ||
>  		    (pmc = get_fixed_pmc(pmu, msr))) {
> @@ -340,6 +408,7 @@ static void intel_pmu_reset(struct kvm_vcpu *vcpu)
> 
>  	pmu->fixed_ctr_ctrl = pmu->global_ctrl = pmu->global_status =
>  		pmu->global_ovf_ctrl = 0;
> +	pmu->kvm_pv_lbr_ctrl = 0;
>  }
> 
>  struct kvm_pmu_ops intel_pmu_ops = {
> --
> 2.7.4
Andi Kleen Sept. 18, 2018, 2:56 a.m. UTC | #4 
> > From: Like Xu <like.xu@intel.com>
> > 
> > This patch adds support to KVM to save/restore the lbr stack on vCPU
> > context switching.
> > 
> > When the guest sets the ACTIVE bit of MSR_KVM_PV_LBR_CTRL, a perf event
> > is created on the host for the related vCPU. This perf event ensures the
> > LBR stack to be saved/restored when the vCPU thread is scheduled out/in.
> > The perf event is removed and freed when the guest clears the ACTIVE
> > bit.
> > 
> 
> What about live migration? Does LBR stack need to be saved on the source side and
> restored on the dest side with the passthrough mode?

Yes it should. Either for call stack LBR, or when it is frozen/disabled.

When it's not frozen/disabled and not in call stack LBR mode it likely doesn't
hurt either, but it's not strictly needed because it will
be replaced so quickly.

-Andi
Wang, Wei W Sept. 18, 2018, 9:57 a.m. UTC | #5 
On 09/18/2018 10:56 AM, Andi Kleen wrote:
>>> From: Like Xu <like.xu@intel.com>
>>>
>>> This patch adds support to KVM to save/restore the lbr stack on vCPU
>>> context switching.
>>>
>>> When the guest sets the ACTIVE bit of MSR_KVM_PV_LBR_CTRL, a perf event
>>> is created on the host for the related vCPU. This perf event ensures the
>>> LBR stack to be saved/restored when the vCPU thread is scheduled out/in.
>>> The perf event is removed and freed when the guest clears the ACTIVE
>>> bit.
>>>
>> What about live migration? Does LBR stack need to be saved on the source side and
>> restored on the dest side with the passthrough mode?
> Yes it should. Either for call stack LBR, or when it is frozen/disabled.
>
> When it's not frozen/disabled and not in call stack LBR mode it likely doesn't
> hurt either, but it's not strictly needed because it will
> be replaced so quickly.

Yes, should be supported. We are working on v3 with the suggested lazy 
save approach, and will send it out shortly.

Best,
Wei
Gonglei (Arei) Sept. 18, 2018, 10:34 a.m. UTC | #6 
> -----Original Message-----
> From: Wei Wang [mailto:wei.w.wang@intel.com]
> Sent: Tuesday, September 18, 2018 5:58 PM
> To: Andi Kleen <ak@linux.intel.com>; Gonglei (Arei) <arei.gonglei@huawei.com>
> Cc: linux-kernel@vger.kernel.org; kvm@vger.kernel.org; pbonzini@redhat.com;
> kan.liang@intel.com; peterz@infradead.org; mingo@redhat.com;
> rkrcmar@redhat.com; like.xu@intel.com
> Subject: Re: [PATCH v2 7/8] KVM: PMU: support to save/restore the guest lbr
> stack on vCPU switching
> 
> On 09/18/2018 10:56 AM, Andi Kleen wrote:
> >>> From: Like Xu <like.xu@intel.com>
> >>>
> >>> This patch adds support to KVM to save/restore the lbr stack on vCPU
> >>> context switching.
> >>>
> >>> When the guest sets the ACTIVE bit of MSR_KVM_PV_LBR_CTRL, a perf
> event
> >>> is created on the host for the related vCPU. This perf event ensures the
> >>> LBR stack to be saved/restored when the vCPU thread is scheduled out/in.
> >>> The perf event is removed and freed when the guest clears the ACTIVE
> >>> bit.
> >>>
> >> What about live migration? Does LBR stack need to be saved on the source
> side and
> >> restored on the dest side with the passthrough mode?
> > Yes it should. Either for call stack LBR, or when it is frozen/disabled.
> >
> > When it's not frozen/disabled and not in call stack LBR mode it likely doesn't
> > hurt either, but it's not strictly needed because it will
> > be replaced so quickly.
> 
> Yes, should be supported. We are working on v3 with the suggested lazy
> save approach, and will send it out shortly.
> 
Nice~ 

Thanks,
-Gonglei
diff mbox series

Patch

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 5db5ba3..cfbe90f 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -432,6 +432,8 @@  struct kvm_pmu {
 	struct kvm_pmc fixed_counters[INTEL_PMC_MAX_FIXED];
 	struct irq_work irq_work;
 	u64 reprogram_pmi;
+	u64 kvm_pv_lbr_ctrl;
+	struct perf_event *guest_lbr_event;
 };
 
 struct kvm_pmu_ops;
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 3b8a57b..8550eee 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -622,7 +622,8 @@  static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 			     (1 << KVM_FEATURE_PV_UNHALT) |
 			     (1 << KVM_FEATURE_PV_TLB_FLUSH) |
 			     (1 << KVM_FEATURE_ASYNC_PF_VMEXIT) |
-			     (1 << KVM_FEATURE_PV_SEND_IPI);
+			     (1 << KVM_FEATURE_PV_SEND_IPI) |
+			     (1 << KVM_FEATURE_PV_LBR_CTRL);
 
 		if (sched_info_on())
 			entry->eax |= (1 << KVM_FEATURE_STEAL_TIME);
diff --git a/arch/x86/kvm/pmu_intel.c b/arch/x86/kvm/pmu_intel.c
index 5ab4a36..27c028d 100644
--- a/arch/x86/kvm/pmu_intel.c
+++ b/arch/x86/kvm/pmu_intel.c
@@ -67,6 +67,62 @@  static void global_ctrl_changed(struct kvm_pmu *pmu, u64 data)
 		reprogram_counter(pmu, bit);
 }
 
+static void guest_lbr_event_create(struct kvm_pmu *pmu)
+{
+	struct perf_event *event;
+	struct perf_event_attr attr = {
+		.type = PERF_TYPE_RAW,
+		.size = sizeof(attr),
+		.pinned = true,
+		.exclude_host = true,
+		.sample_type = PERF_SAMPLE_BRANCH_STACK,
+		.branch_sample_type = PERF_SAMPLE_BRANCH_CALL_STACK |
+				      PERF_SAMPLE_BRANCH_USER |
+				      PERF_SAMPLE_BRANCH_KERNEL,
+	};
+
+	if (unlikely(pmu->guest_lbr_event)) {
+		pr_err("%s: guest_lbr_event already created\n", __func__);
+		return;
+	}
+
+	event = perf_event_create_kernel_counter(&attr, -1, current, NULL,
+						 NULL);
+	if (IS_ERR(event)) {
+		pr_err("%s: failed %ld\n", __func__, PTR_ERR(event));
+		return;
+	}
+	pmu->guest_lbr_event = event;
+}
+
+void guest_lbr_event_release(struct kvm_pmu *pmu)
+{
+	struct perf_event *event = pmu->guest_lbr_event;
+
+	if (unlikely(!pmu->guest_lbr_event)) {
+		pr_err("%s: guest_lbr_event already freed\n", __func__);
+		return;
+	}
+
+	if (event) {
+		event->pmu->stop(event, PERF_EF_UPDATE);
+		perf_event_release_kernel(event);
+	}
+	pmu->guest_lbr_event = NULL;
+}
+
+static void kvm_pv_lbr_ctrl_changed(struct kvm_pmu *pmu, u64 data)
+{
+	bool guest_lbr_active = data & KVM_PV_LBR_CTRL_ACTIVE;
+
+	if (guest_lbr_active)
+		guest_lbr_event_create(pmu);
+	else
+		guest_lbr_event_release(pmu);
+
+	pmu->kvm_pv_lbr_ctrl = data;
+}
+
 static unsigned intel_find_arch_event(struct kvm_pmu *pmu,
 				      u8 event_select,
 				      u8 unit_mask)
@@ -145,7 +201,7 @@  static struct kvm_pmc *intel_msr_idx_to_pmc(struct kvm_vcpu *vcpu,
 static bool intel_is_valid_msr(struct kvm_vcpu *vcpu, u32 msr)
 {
 	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
-	int ret;
+	int ret = 0;
 
 	switch (msr) {
 	case MSR_CORE_PERF_FIXED_CTR_CTRL:
@@ -154,6 +210,10 @@  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_KVM_PV_LBR_CTRL:
+		if (vcpu->kvm->arch.guest_lbr)
+			ret = 1;
+		break;
 	default:
 		ret = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0) ||
 			get_gp_pmc(pmu, msr, MSR_P6_EVNTSEL0) ||
@@ -182,6 +242,9 @@  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_KVM_PV_LBR_CTRL:
+		*data = pmu->kvm_pv_lbr_ctrl;
+		return 0;
 	default:
 		if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0)) ||
 		    (pmc = get_fixed_pmc(pmu, msr))) {
@@ -234,6 +297,11 @@  static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 			return 0;
 		}
 		break;
+	case MSR_KVM_PV_LBR_CTRL:
+		if (pmu->kvm_pv_lbr_ctrl == data)
+			return 0;
+		kvm_pv_lbr_ctrl_changed(pmu, data);
+		return 0;
 	default:
 		if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0)) ||
 		    (pmc = get_fixed_pmc(pmu, msr))) {
@@ -340,6 +408,7 @@  static void intel_pmu_reset(struct kvm_vcpu *vcpu)
 
 	pmu->fixed_ctr_ctrl = pmu->global_ctrl = pmu->global_status =
 		pmu->global_ovf_ctrl = 0;
+	pmu->kvm_pv_lbr_ctrl = 0;
 }
 
 struct kvm_pmu_ops intel_pmu_ops = {