linux-kernel - [PATCH V4 2/2] kvm: ignore LBR and extra

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Date:	Tue,  8 Jul 2014 09:49:41 -0700
From:	kan.liang@...el.com
To:	peterz@...radead.org
Cc:	andi@...stfloor.org, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, Kan Liang <kan.liang@...el.com>,
	Andi Kleen <ak@...ux.intel.com>
Subject: [PATCH V4 2/2] kvm: ignore LBR and extra_regs

From: Kan Liang <kan.liang@...el.com>

With -cpu host KVM reports LBR and extra_regs support, so the perf driver may accesses the LBR and extra_regs MSRs.
However, there is no LBR and extra_regs virtualization support yet. This could causes guest to crash.
As a workaround, KVM just simply ignore the LBR and extra_regs MSRs to lie the guest.

For reproducing the issue, please build the kernel with CONFIG_KVM_INTEL = y (for host kernel).
And CONFIG_PARAVIRT = n and CONFIG_KVM_GUEST = n (for guest kernel).
Start the guest with -cpu host.
Run perf record with --branch-any or --branch-filter in guest to trigger LBR #GP.
Run perf stat offcore events (E.g. LLC-loads/LLC-load-misses ...) in guest to trigger offcore_rsp #GP

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
Signed-off-by: Kan Liang <kan.liang@...el.com>

V3: add MSR_LBR_TOS
V4: add MSR_LBR_SELECT and MSR_PEBS_LD_LAT_THRESHOLD
---
 arch/x86/kvm/pmu.c | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index cbecaa9..cf0ed39 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -331,6 +331,18 @@ bool kvm_pmu_msr(struct kvm_vcpu *vcpu, u32 msr)
 	case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
 		ret = pmu->version > 1;
 		break;
+	case MSR_OFFCORE_RSP_0:
+	case MSR_OFFCORE_RSP_1:
+	case MSR_LBR_SELECT:
+	case MSR_PEBS_LD_LAT_THRESHOLD:
+	case MSR_LBR_TOS:
+	/* At most 8-deep LBR for core and atom */
+	case MSR_LBR_CORE_FROM ... MSR_LBR_CORE_FROM + 7:
+	case MSR_LBR_CORE_TO ... MSR_LBR_CORE_TO + 7:
+	/* 16-deep LBR for core i3/i5/i7 series processors */
+	case MSR_LBR_NHM_FROM ... MSR_LBR_NHM_FROM + 15:
+	case MSR_LBR_NHM_TO ... MSR_LBR_NHM_TO + 15:
+		return 1; /* to avoid crashes */
 	default:
 		ret = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0)
 			|| get_gp_pmc(pmu, msr, MSR_P6_EVNTSEL0)
@@ -358,6 +370,19 @@ int kvm_pmu_get_msr(struct kvm_vcpu *vcpu, u32 index, u64 *data)
 	case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
 		*data = pmu->global_ovf_ctrl;
 		return 0;
+	case MSR_OFFCORE_RSP_0:
+	case MSR_OFFCORE_RSP_1:
+	case MSR_LBR_SELECT:
+	case MSR_PEBS_LD_LAT_THRESHOLD:
+	case MSR_LBR_TOS:
+	/* At most 8-deep LBR for core and atom */
+	case MSR_LBR_CORE_FROM ... MSR_LBR_CORE_FROM + 7:
+	case MSR_LBR_CORE_TO ... MSR_LBR_CORE_TO + 7:
+	/* 16-deep LBR for core i3/i5/i7 series processors */
+	case MSR_LBR_NHM_FROM ... MSR_LBR_NHM_FROM + 15:
+	case MSR_LBR_NHM_TO ... MSR_LBR_NHM_TO + 15:
+		*data = 0;
+		return 0;
 	default:
 		if ((pmc = get_gp_pmc(pmu, index, MSR_IA32_PERFCTR0)) ||
 				(pmc = get_fixed_pmc(pmu, index))) {
@@ -409,6 +434,19 @@ int kvm_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 			return 0;
 		}
 		break;
+	case MSR_OFFCORE_RSP_0:
+	case MSR_OFFCORE_RSP_1:
+	case MSR_LBR_SELECT:
+	case MSR_PEBS_LD_LAT_THRESHOLD:
+	case MSR_LBR_TOS:
+	/* At most 8-deep LBR for core and atom */
+	case MSR_LBR_CORE_FROM ... MSR_LBR_CORE_FROM + 7:
+	case MSR_LBR_CORE_TO ... MSR_LBR_CORE_TO + 7:
+	/* 16-deep LBR for core i3/i5/i7 series processors */
+	case MSR_LBR_NHM_FROM ... MSR_LBR_NHM_FROM + 15:
+	case MSR_LBR_NHM_TO ... MSR_LBR_NHM_TO + 15:
+		/* dummy for now */
+		break;
 	default:
 		if ((pmc = get_gp_pmc(pmu, index, MSR_IA32_PERFCTR0)) ||
 				(pmc = get_fixed_pmc(pmu, index))) {
-- 
1.8.3.1

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