[PATCH v2 1/4] KVM: vmx/pmu: Add MSR_ARCH_LBR_DEPTH emulation for Arch LBR

[Like Xu <like.xu@linux.intel.com>]

The number of Arch LBR entries available for recording operations
is dictated by the value in MSR_ARCH_LBR_DEPTH.DEPTH. The supported
LBR depth values can be found in CPUID.(EAX=01CH, ECX=0):EAX[7:0]
and for each bit n set in this field, the MSR_ARCH_LBR_DEPTH.DEPTH
value 8*(n+1) is supported.

On a software write to MSR_ARCH_LBR_DEPTH, all LBR entries are reset
to 0. Emulate the reset behavior by introducing lbr_desc->arch_lbr_reset
and sync it to the host MSR_ARCH_LBR_DEPTH msr when the guest LBR
event is ACTIVE and the LBR records msrs are pass-through to the guest.

Signed-off-by: Like Xu <like.xu@linux.intel.com>
---
 arch/x86/kvm/vmx/pmu_intel.c | 43 ++++++++++++++++++++++++++++++++++++
 arch/x86/kvm/vmx/vmx.h       |  3 +++
 2 files changed, 46 insertions(+)

diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index d1df618cb7de..b550c4a6ce33 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -220,6 +220,9 @@ 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_ARCH_LBR_DEPTH:
+		ret = guest_cpuid_has(vcpu, X86_FEATURE_ARCH_LBR);
+		break;
 	default:
 		ret = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0) ||
 			get_gp_pmc(pmu, msr, MSR_P6_EVNTSEL0) ||
@@ -250,6 +253,7 @@ static inline void intel_pmu_release_guest_lbr_event(struct kvm_vcpu *vcpu)
 	if (lbr_desc->event) {
 		perf_event_release_kernel(lbr_desc->event);
 		lbr_desc->event = NULL;
+		lbr_desc->arch_lbr_reset = false;
 		vcpu_to_pmu(vcpu)->event_count--;
 	}
 }
@@ -348,10 +352,26 @@ static bool intel_pmu_handle_lbr_msrs_access(struct kvm_vcpu *vcpu,
 	return true;
 }
 
+/*
+ * Check if the requested depth values is supported
+ * based on the bits [0:7] of the guest cpuid.1c.eax.
+ */
+static bool arch_lbr_depth_is_valid(struct kvm_vcpu *vcpu, u64 depth)
+{
+	struct kvm_cpuid_entry2 *best;
+
+	best = kvm_find_cpuid_entry(vcpu, 0x1c, 0);
+	if (depth && best)
+		return (best->eax & 0xff) & (1ULL << (depth / 8 - 1));
+
+	return false;
+}
+
 static int intel_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 {
 	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
 	struct kvm_pmc *pmc;
+	struct lbr_desc *lbr_desc = vcpu_to_lbr_desc(vcpu);
 	u32 msr = msr_info->index;
 
 	switch (msr) {
@@ -367,6 +387,9 @@ static int intel_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
 		msr_info->data = pmu->global_ovf_ctrl;
 		return 0;
+	case MSR_ARCH_LBR_DEPTH:
+		msr_info->data = lbr_desc->records.nr;
+		return 0;
 	default:
 		if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0)) ||
 		    (pmc = get_gp_pmc(pmu, msr, MSR_IA32_PMC0))) {
@@ -393,6 +416,7 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 {
 	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
 	struct kvm_pmc *pmc;
+	struct lbr_desc *lbr_desc = vcpu_to_lbr_desc(vcpu);
 	u32 msr = msr_info->index;
 	u64 data = msr_info->data;
 
@@ -427,6 +451,13 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 			return 0;
 		}
 		break;
+	case MSR_ARCH_LBR_DEPTH:
+		if (!arch_lbr_depth_is_valid(vcpu, data))
+			return 1;
+		lbr_desc->records.nr = data;
+		lbr_desc->arch_lbr_reset = true;
+		__set_bit(INTEL_PMC_IDX_FIXED_VLBR, pmu->pmc_in_use);
+		return 0;
 	default:
 		if ((pmc = get_gp_pmc(pmu, msr, MSR_IA32_PERFCTR0)) ||
 		    (pmc = get_gp_pmc(pmu, msr, MSR_IA32_PMC0))) {
@@ -566,6 +597,7 @@ static void intel_pmu_init(struct kvm_vcpu *vcpu)
 	lbr_desc->records.nr = 0;
 	lbr_desc->event = NULL;
 	lbr_desc->msr_passthrough = false;
+	lbr_desc->arch_lbr_reset = false;
 }
 
 static void intel_pmu_reset(struct kvm_vcpu *vcpu)
@@ -623,6 +655,14 @@ static void intel_pmu_deliver_pmi(struct kvm_vcpu *vcpu)
 		intel_pmu_legacy_freezing_lbrs_on_pmi(vcpu);
 }
 
+static void intel_pmu_arch_lbr_reset(struct kvm_vcpu *vcpu)
+{
+	struct lbr_desc *lbr_desc = vcpu_to_lbr_desc(vcpu);
+
+	wrmsrl(MSR_ARCH_LBR_DEPTH, lbr_desc->records.nr);
+	lbr_desc->arch_lbr_reset = false;
+}
+
 static void vmx_update_intercept_for_lbr_msrs(struct kvm_vcpu *vcpu, bool set)
 {
 	struct x86_pmu_lbr *lbr = vcpu_to_lbr_records(vcpu);
@@ -654,6 +694,9 @@ static inline void vmx_enable_lbr_msrs_passthrough(struct kvm_vcpu *vcpu)
 {
 	struct lbr_desc *lbr_desc = vcpu_to_lbr_desc(vcpu);
 
+	if (unlikely(lbr_desc->arch_lbr_reset))
+		intel_pmu_arch_lbr_reset(vcpu);
+
 	if (lbr_desc->msr_passthrough)
 		return;
 
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 12c53d05a902..ad8abe203ba5 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -116,6 +116,9 @@ struct lbr_desc {
 
 	/* True if LBRs are marked as not intercepted in the MSR bitmap */
 	bool msr_passthrough;
+
+	/* Reset all LBR entries on a guest write to MSR_ARCH_LBR_DEPTH */
+	bool arch_lbr_reset;
 };
 
 /*
-- 
2.29.2