linux-kernel - [PATCH v3 2/3] KVM: vPMU: Fill get_msr MSR_CORE_PERF_GLOBAL_OVF

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Date:   Tue, 19 Oct 2021 01:12:39 -0700
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: [PATCH v3 2/3] KVM: vPMU: Fill get_msr MSR_CORE_PERF_GLOBAL_OVF_CTRL w/ 0

From: Wanpeng Li <wanpengli@...cent.com>

SDM section 18.2.3 mentioned that:

  "IA32_PERF_GLOBAL_OVF_CTL MSR allows software to clear overflow indicator(s) of
   any general-purpose or fixed-function counters via a single WRMSR."

It is R/W mentioned by SDM, we read this msr on bare-metal during perf testing,
the value is always 0 for ICX/SKX boxes on hands. Let's fill get_msr
MSR_CORE_PERF_GLOBAL_OVF_CTRL w/ 0 as hardware behavior and drop
global_ovf_ctrl variable.

Tested-by: Like Xu <likexu@...cent.com>
Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
Btw, xen also fills get_msr MSR_CORE_PERF_GLOBAL_OVF_CTRL w/ 0.
v1 -> v2:
 * drop 'u64 global_ovf_ctrl' directly

 arch/x86/include/asm/kvm_host.h | 1 -
 arch/x86/kvm/vmx/pmu_intel.c    | 6 ++----
 2 files changed, 2 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index f8f48a7ec577..7aaac918e992 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -499,7 +499,6 @@ struct kvm_pmu {
 	u64 fixed_ctr_ctrl;
 	u64 global_ctrl;
 	u64 global_status;
-	u64 global_ovf_ctrl;
 	u64 counter_bitmask[2];
 	u64 global_ctrl_mask;
 	u64 global_ovf_ctrl_mask;
diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index 10cc4f65c4ef..b8e0d21b7c8a 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -365,7 +365,7 @@ static int intel_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		msr_info->data = pmu->global_ctrl;
 		return 0;
 	case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
-		msr_info->data = pmu->global_ovf_ctrl;
+		msr_info->data = 0;
 		return 0;
 	default:
 		if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0)) ||
@@ -423,7 +423,6 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		if (!(data & pmu->global_ovf_ctrl_mask)) {
 			if (!msr_info->host_initiated)
 				pmu->global_status &= ~data;
-			pmu->global_ovf_ctrl = data;
 			return 0;
 		}
 		break;
@@ -588,8 +587,7 @@ static void intel_pmu_reset(struct kvm_vcpu *vcpu)
 		pmc->counter = 0;
 	}
 
-	pmu->fixed_ctr_ctrl = pmu->global_ctrl = pmu->global_status =
-		pmu->global_ovf_ctrl = 0;
+	pmu->fixed_ctr_ctrl = pmu->global_ctrl = pmu->global_status = 0;
 
 	intel_pmu_release_guest_lbr_event(vcpu);
 }
-- 
2.25.1