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

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Date:   Fri,  8 Oct 2021 02:57:33 -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 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 CLX/SKX boxes on hands. Let's fill get_msr
MSR_CORE_PERF_GLOBAL_OVF_CTRL w/ 0 as hardware behavior.

Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
Btw, xen also fills get_msr MSR_CORE_PERF_GLOBAL_OVF_CTRL 0.

 arch/x86/kvm/vmx/pmu_intel.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index 10cc4f65c4ef..47260a8563f9 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)) ||
-- 
2.25.1