[PATCH v3 12/18] KVM: x86/pmu: Emulate IA32_PERF_GLOBAL_INUSE MSR

[Zide Chen]

Intel PerfMon v4 introduces IA32_PERF_GLOBAL_INUSE (0x392) to track
which counters and the PMI are currently claimed by software agents,
allowing independent software agents to check counter availability
without a shared scheduler arbitrating between them.

IA32_PERF_GLOBAL_INUSE is a read-only MSR, and any write attempt
results in a #GP. The MSR is not part of the VM state, so it does
not need to be advertised to userspace, nor saved and restored during
live migration.

Always intercept IA32_PERF_GLOBAL_INUSE to prevent the guest from
erroneously observing filtered fixed counters as idle.

Originally-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
Signed-off-by: Zide Chen <zide.chen@xxxxxxxxx>
---
v3:
- Split from combined v2 patch into standalone GLOBAL_INUSE patch.
- Always intercept MSR_CORE_PERF_GLOBAL_INUSE. (Jim)
- Use '!!' for explicit boolean conversion. (Jim)
- Relocate PERF_GLOBAL_INUSE_PMI_INUSE to perf_event.h.

v2:
- Change intel_pmu_get_global_inuse() to return u64, to match the
  surrounding code style.
- Add the missing vmcs02 updates for these two MSRs.
- Change "> 3" to ">= 4" to make the "v4-gated" more obvious and match
  the existing code style.
---
 arch/x86/include/asm/msr-index.h  |  1 +
 arch/x86/include/asm/perf_event.h |  3 +++
 arch/x86/kvm/vmx/pmu_intel.c      | 36 +++++++++++++++++++++++++++++++
 3 files changed, 40 insertions(+)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 30cd04c0ace9..25dda50fbdc1 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -1242,6 +1242,7 @@
 #define MSR_CORE_PERF_GLOBAL_CTRL	0x0000038f
 #define MSR_CORE_PERF_GLOBAL_OVF_CTRL	0x00000390
 #define MSR_CORE_PERF_GLOBAL_STATUS_SET	0x00000391
+#define MSR_CORE_PERF_GLOBAL_INUSE	0x00000392
 
 #define MSR_PERF_METRICS		0x00000329
 
diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
index 17b0bc7dfce7..2937e8a27891 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -454,6 +454,9 @@ static inline bool is_topdown_idx(int idx)
 #define GLOBAL_STATUS_ARCH_PEBS_THRESHOLD	BIT_ULL(GLOBAL_STATUS_ARCH_PEBS_THRESHOLD_BIT)
 #define GLOBAL_STATUS_PERF_METRICS_OVF_BIT	48
 
+/* Intel IA32_PERF_GLOBAL_INUSE MSR */
+#define PERF_GLOBAL_INUSE_PMI_INUSE	BIT_ULL(63)
+
 #define GLOBAL_CTRL_EN_PERF_METRICS		BIT_ULL(48)
 /*
  * We model guest LBR event tracing as another fixed-mode PMC like BTS.
diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index e81a3f8b9b02..1372091dc1f8 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -198,6 +198,7 @@ static bool intel_is_valid_msr(struct kvm_vcpu *vcpu, u32 msr)
 	case MSR_CORE_PERF_FIXED_CTR_CTRL:
 		return kvm_pmu_has_perf_global_ctrl(pmu);
 	case MSR_CORE_PERF_GLOBAL_STATUS_SET:
+	case MSR_CORE_PERF_GLOBAL_INUSE:
 		return pmu->version >= 4;
 	case MSR_IA32_PEBS_ENABLE:
 		ret = vcpu_get_perf_capabilities(vcpu) & PERF_CAP_PEBS_FORMAT;
@@ -346,6 +347,38 @@ static bool intel_pmu_handle_lbr_msrs_access(struct kvm_vcpu *vcpu,
 	return true;
 }
 
+static u64 intel_pmu_get_global_inuse(struct kvm_vcpu *vcpu)
+{
+	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
+	unsigned long fixed_mask = kvm_fixed_pmc_mask(pmu);
+	unsigned long gp_mask = kvm_gp_pmc_mask(pmu);
+	bool pmi_inuse = false;
+	u64 eventsel, data = 0;
+	u32 fixed_ctrl;
+	int i;
+
+	kvm_for_each_gp_counter(i, gp_mask) {
+		eventsel = pmu->gp_counters[i].eventsel;
+
+		if (eventsel & ARCH_PERFMON_EVENTSEL_EVENT)
+			data |= BIT_ULL(i);
+		pmi_inuse |= !!(eventsel & ARCH_PERFMON_EVENTSEL_INT);
+	}
+	kvm_for_each_fixed_counter(i, fixed_mask) {
+		fixed_ctrl = fixed_ctrl_field(pmu->fixed_ctr_ctrl, i);
+
+		if (fixed_ctrl & (INTEL_FIXED_0_KERNEL | INTEL_FIXED_0_USER))
+			data |= BIT_ULL(KVM_FIXED_PMC_BASE_IDX + i);
+		pmi_inuse |= !!(fixed_ctrl & INTEL_FIXED_0_ENABLE_PMI);
+	}
+	pmi_inuse |= pmu->pebs_enable;
+
+	if (pmi_inuse)
+		data |= PERF_GLOBAL_INUSE_PMI_INUSE;
+
+	return data;
+}
+
 static int intel_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 {
 	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
@@ -356,6 +389,9 @@ static int intel_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case MSR_CORE_PERF_FIXED_CTR_CTRL:
 		msr_info->data = pmu->fixed_ctr_ctrl;
 		break;
+	case MSR_CORE_PERF_GLOBAL_INUSE:
+		msr_info->data = intel_pmu_get_global_inuse(vcpu);
+		break;
 	case MSR_IA32_PEBS_ENABLE:
 		msr_info->data = pmu->pebs_enable;
 		break;
-- 
2.56.0