[PATCH 11/15] KVM: x86/pmu: Emulate streamlined Freeze-LBR-on-PMI

[Zide Chen]

PerfMon v4 streamlined the Freeze-LBR-on-PMI mechanism. When
DEBUGCTLMSR_FREEZE_LBRS_ON_PMI is set and a PMI fires, hardware sets
IA32_PERF_GLOBAL_STATUS.LBR_Frz instead of clearing DEBUGCTLMSR_LBR.

Guest PerfMon v4+ is supported under mediated vPMU only. When KVM
relays a guest-induced PMI, the mediated vPMU framework already
propagates IA32_PERF_GLOBAL_STATUS.LBR_Frz, and no additional handling
is required.

For PMIs generated by KVM-emulated PMU events, however, KVM must
emulate IA32_PERF_GLOBAL_STATUS.LBR_Frz so that guest LBR recording
is frozen as required by the architectural behavior.

Signed-off-by: Zide Chen <zide.chen@xxxxxxxxx>
---
 arch/x86/kvm/vmx/pmu_intel.c | 47 ++++++++++++++++++++++--------------
 1 file changed, 29 insertions(+), 18 deletions(-)

diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index cb6f9c272e03..556c119d5e91 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -660,6 +660,8 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
 
 	pmu->global_status_rsvd = pmu->global_ctrl_rsvd
 			& ~(GLOBAL_STATUS_BUFFER_OVF | GLOBAL_STATUS_COND_CHG);
+	if (pmu->version > 3)
+		pmu->global_status_rsvd &= ~GLOBAL_STATUS_LBRS_FROZEN;
 	if (vmx_pt_mode_is_host_guest())
 		pmu->global_status_rsvd &= ~GLOBAL_STATUS_TRACE_TOPAPMI;
 
@@ -718,32 +720,41 @@ static void intel_pmu_reset(struct kvm_vcpu *vcpu)
 }
 
 /*
- * Emulate LBR_On_PMI behavior for 1 < pmu.version < 4.
- *
- * If Freeze_LBR_On_PMI = 1, the LBR is frozen on PMI and
- * the KVM emulates to clear the LBR bit (bit 0) in IA32_DEBUGCTL.
- *
- * Guest needs to re-enable LBR to resume branches recording.
+ * Emulate legacy and streamlined Freeze_LBR_On_PMI behavior.
+ * In either case, guest needs to re-enable LBR to resume branches recording.
  */
-static void intel_pmu_legacy_freezing_lbrs_on_pmi(struct kvm_vcpu *vcpu)
+static void intel_pmu_freeze_lbr_on_pmi(struct kvm_vcpu *vcpu)
 {
-	u64 data = vmx_guest_debugctl_read();
+	u8 version;
+	u64 data;
 
-	if (data & DEBUGCTLMSR_FREEZE_LBRS_ON_PMI) {
-		data &= ~DEBUGCTLMSR_LBR;
-		vmx_guest_debugctl_write(vcpu, data);
+	if (!intel_pmu_lbr_is_enabled(vcpu))
+		return;
+
+	data = vmx_guest_debugctl_read();
+	version = vcpu_to_pmu(vcpu)->version;
+
+	if (!(data & DEBUGCTLMSR_FREEZE_LBRS_ON_PMI))
+		return;
+
+	if (version > 1 && version < 4) {
+		if (data & DEBUGCTLMSR_LBR) {
+			data &= ~DEBUGCTLMSR_LBR;
+			vmx_guest_debugctl_write(vcpu, data);
+		}
+	} else if (vcpu_to_lbr_desc(vcpu)->msr_passthrough &&
+		   kvm_vcpu_has_mediated_pmu(vcpu)) {
+		/*
+		 * This will be restored to guest before VM-Entry, setting
+		 * LBR_Frz to freeze LBR recording until the guest clears it.
+		 */
+		vcpu_to_pmu(vcpu)->global_status |= GLOBAL_STATUS_LBRS_FROZEN;
 	}
 }
 
 static void intel_pmu_deliver_pmi(struct kvm_vcpu *vcpu)
 {
-	u8 version = vcpu_to_pmu(vcpu)->version;
-
-	if (!intel_pmu_lbr_is_enabled(vcpu))
-		return;
-
-	if (version > 1 && version < 4)
-		intel_pmu_legacy_freezing_lbrs_on_pmi(vcpu);
+	intel_pmu_freeze_lbr_on_pmi(vcpu);
 }
 
 static void vmx_update_intercept_for_lbr_msrs(struct kvm_vcpu *vcpu, bool set)
-- 
2.54.0