[PATCH 1/3] KVM: x86/pmu: Do not map fixed counters >= 3 to generic perf events

[Zide Chen]

Only fixed counters 0..2 have matching generic cross-platform
hardware perf events (INSTRUCTIONS, CPU_CYCLES, REF_CPU_CYCLES).
Therefore, perf_get_hw_event_config() is only applicable to these
counters.

KVM does not intend to emulate fixed counters >= 3 on legacy
(non-mediated) vPMU, while for mediated vPMU, KVM does not care what
the fixed counter event mappings are.  Therefore, return 0 for their
eventsel.

Also remove __always_inline as BUILD_BUG_ON() is no longer needed.

Signed-off-by: Zide Chen <zide.chen@xxxxxxxxx>
---
 arch/x86/kvm/vmx/pmu_intel.c | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index 27eb76e6b6a0..4bfd16a9e6c7 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -454,28 +454,30 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
  * different perf_event is already utilizing the requested counter, but the end
  * result is the same (ignoring the fact that using a general purpose counter
  * will likely exacerbate counter contention).
- *
- * Forcibly inlined to allow asserting on @index at build time, and there should
- * never be more than one user.
  */
-static __always_inline u64 intel_get_fixed_pmc_eventsel(unsigned int index)
+static u64 intel_get_fixed_pmc_eventsel(unsigned int index)
 {
 	const enum perf_hw_id fixed_pmc_perf_ids[] = {
 		[0] = PERF_COUNT_HW_INSTRUCTIONS,
 		[1] = PERF_COUNT_HW_CPU_CYCLES,
 		[2] = PERF_COUNT_HW_REF_CPU_CYCLES,
 	};
-	u64 eventsel;
-
-	BUILD_BUG_ON(ARRAY_SIZE(fixed_pmc_perf_ids) != KVM_MAX_NR_INTEL_FIXED_COUNTERS);
-	BUILD_BUG_ON(index >= KVM_MAX_NR_INTEL_FIXED_COUNTERS);
+	u64 eventsel = 0;
 
 	/*
-	 * Yell if perf reports support for a fixed counter but perf doesn't
-	 * have a known encoding for the associated general purpose event.
+	 * Fixed counters 3 and above don't have corresponding generic hardware
+	 * perf event, and KVM does not intend to emulate them on non-mediated
+	 * vPMU.
 	 */
-	eventsel = perf_get_hw_event_config(fixed_pmc_perf_ids[index]);
-	WARN_ON_ONCE(!eventsel && index < kvm_pmu_cap.num_counters_fixed);
+	if (index < 3) {
+		/*
+		 * Yell if perf reports support for a fixed counter but perf
+		 * doesn't have a known encoding for the associated general
+		 * purpose event.
+		 */
+		eventsel = perf_get_hw_event_config(fixed_pmc_perf_ids[index]);
+		WARN_ON_ONCE(!eventsel && index < kvm_pmu_cap.num_counters_fixed);
+	}
 	return eventsel;
 }
 
-- 
2.53.0