[PATCH V2 2/4] 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>
---
V2:
- Don't advertise fixed counter 3 to userspace if the host doesn't
  support it.
---
 arch/x86/include/asm/kvm_host.h | 2 +-
 arch/x86/kvm/cpuid.c            | 9 +++++++--
 arch/x86/kvm/pmu.c              | 4 ++++
 arch/x86/kvm/x86.c              | 4 ++--
 4 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index c470e40a00aa..cb736a4c72ea 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -556,7 +556,7 @@ 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/cpuid.c b/arch/x86/kvm/cpuid.c
index e69156b54cff..d87a26f740e5 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -1505,7 +1505,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 		break;
 	case 0xa: { /* Architectural Performance Monitoring */
 		union cpuid10_eax eax = { };
-		union cpuid10_edx edx = { };
+		union cpuid10_edx edx = { }, host_edx;
 
 		if (!enable_pmu || !static_cpu_has(X86_FEATURE_ARCH_PERFMON)) {
 			entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
@@ -1516,9 +1516,14 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 		eax.split.num_counters = kvm_pmu_cap.num_counters_gp;
 		eax.split.bit_width = kvm_pmu_cap.bit_width_gp;
 		eax.split.mask_length = kvm_pmu_cap.events_mask_len;
-		edx.split.num_counters_fixed = kvm_pmu_cap.num_counters_fixed;
 		edx.split.bit_width_fixed = kvm_pmu_cap.bit_width_fixed;
 
+		/* Guest does not support non-contiguous fixed counters. */
+		host_edx = (union cpuid10_edx)entry->edx;
+		edx.split.num_counters_fixed =
+			 min_t(int, kvm_pmu_cap.num_counters_fixed,
+			       host_edx.split.num_counters_fixed);
+
 		if (kvm_pmu_cap.version)
 			edx.split.anythread_deprecated = 1;
 
diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index e218352e3423..9ff4a6a9cd0b 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -148,12 +148,16 @@ void kvm_init_pmu_capability(struct kvm_pmu_ops *pmu_ops)
 	}
 
 	memcpy(&kvm_pmu_cap, &kvm_host_pmu, sizeof(kvm_host_pmu));
+
 	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);
 	kvm_pmu_cap.num_counters_fixed = min(kvm_pmu_cap.num_counters_fixed,
 					     KVM_MAX_NR_FIXED_COUNTERS);
 
+	if (!enable_mediated_pmu && kvm_pmu_cap.num_counters_fixed > 3)
+		kvm_pmu_cap.num_counters_fixed = 3;
+
 	kvm_pmu_eventsel.INSTRUCTIONS_RETIRED =
 		perf_get_hw_event_config(PERF_COUNT_HW_INSTRUCTIONS);
 	kvm_pmu_eventsel.BRANCH_INSTRUCTIONS_RETIRED =
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0a1b63c63d1a..604072d9354f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -360,7 +360,7 @@ 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,
@@ -7756,7 +7756,7 @@ 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;
-- 
2.54.0