[PATCH 2/3] KVM: x86/pmu: Support Intel fixed counter 3 on mediated vPMU

[Zide Chen]

From: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>

Starting with Ice Lake, Intel introduces fixed counter 3, which counts
TOPDOWN.SLOTS - the number of available slots for an unhalted logical
processor.  It serves as the denominator for top-level metrics in the
Top-down Microarchitecture Analysis method.

Emulating this counter on legacy vPMU would require introducing a new
generic perf encoding for the Intel-specific TOPDOWN.SLOTS event in
order to call perf_get_hw_event_config().  This is undesirable as it
would pollute the generic perf event encoding.

Moreover, KVM does not intend to emulate IA32_PERF_METRICS in the
legacy vPMU model, and without IA32_PERF_METRICS, emulating this
counter has little practical value.  Therefore, expose fixed counter
3 to guests only when mediated vPMU is enabled.

Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
Co-developed-by: Zide Chen <zide.chen@xxxxxxxxx>
Signed-off-by: Zide Chen <zide.chen@xxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h | 2 +-
 arch/x86/kvm/pmu.c              | 4 ++++
 arch/x86/kvm/x86.c              | 4 ++--
 3 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index ff07c45e3c73..4666b2c7988f 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -555,7 +555,7 @@ struct kvm_pmc {
 #define KVM_MAX_NR_GP_COUNTERS		KVM_MAX(KVM_MAX_NR_INTEL_GP_COUNTERS, \
 						KVM_MAX_NR_AMD_GP_COUNTERS)
 
-#define KVM_MAX_NR_INTEL_FIXED_COUNTERS	3
+#define KVM_MAX_NR_INTEL_FIXED_COUNTERS	4
 #define KVM_MAX_NR_AMD_FIXED_COUNTERS	0
 #define KVM_MAX_NR_FIXED_COUNTERS	KVM_MAX(KVM_MAX_NR_INTEL_FIXED_COUNTERS, \
 						KVM_MAX_NR_AMD_FIXED_COUNTERS)
diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index bd6b785cf261..ee49395bfb82 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -148,6 +148,10 @@ void kvm_init_pmu_capability(struct kvm_pmu_ops *pmu_ops)
 	}
 
 	memcpy(&kvm_pmu_cap, &kvm_host_pmu, sizeof(kvm_host_pmu));
+
+	if (!enable_mediated_pmu && kvm_pmu_cap.num_counters_fixed > 3)
+		kvm_pmu_cap.num_counters_fixed = 3;
+
 	kvm_pmu_cap.version = min(kvm_pmu_cap.version, 2);
 	kvm_pmu_cap.num_counters_gp = min(kvm_pmu_cap.num_counters_gp,
 					  pmu_ops->MAX_NR_GP_COUNTERS);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3fb64905d190..2ab7a4958620 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -355,7 +355,7 @@ static const u32 msrs_to_save_base[] = {
 
 static const u32 msrs_to_save_pmu[] = {
 	MSR_ARCH_PERFMON_FIXED_CTR0, MSR_ARCH_PERFMON_FIXED_CTR1,
-	MSR_ARCH_PERFMON_FIXED_CTR0 + 2,
+	MSR_ARCH_PERFMON_FIXED_CTR2, MSR_ARCH_PERFMON_FIXED_CTR3,
 	MSR_CORE_PERF_FIXED_CTR_CTRL, MSR_CORE_PERF_GLOBAL_STATUS,
 	MSR_CORE_PERF_GLOBAL_CTRL,
 	MSR_IA32_PEBS_ENABLE, MSR_IA32_DS_AREA, MSR_PEBS_DATA_CFG,
@@ -7738,7 +7738,7 @@ static void kvm_init_msr_lists(void)
 {
 	unsigned i;
 
-	BUILD_BUG_ON_MSG(KVM_MAX_NR_FIXED_COUNTERS != 3,
+	BUILD_BUG_ON_MSG(KVM_MAX_NR_FIXED_COUNTERS != 4,
 			 "Please update the fixed PMCs in msrs_to_save_pmu[]");
 
 	num_msrs_to_save = 0;
-- 
2.53.0