[PATCH v6 1/8] 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.

The two BUILD_BUG_ON() checks are no longer needed, so drop them along
with __always_inline.

Signed-off-by: Zide Chen <zide.chen@xxxxxxxxx>
---
v6:
- Re-arrange the code for early return. Clearer.
v2:
- Replace 3 in "if (index < 3)" with ARRAY_SIZE(fixed_pmc_perf_ids).
---
 arch/x86/kvm/vmx/pmu_intel.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index a73a9515d96c..f15af497d27f 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -464,11 +464,8 @@ 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,
@@ -477,8 +474,13 @@ static __always_inline u64 intel_get_fixed_pmc_eventsel(unsigned int index)
 	};
 	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);
+	/*
+	 * Fixed counters 3 and above don't have a corresponding generic
+	 * hardware perf event, and KVM does not intend to emulate them on
+	 * non-mediated vPMU.
+	 */
+	if (index >= ARRAY_SIZE(fixed_pmc_perf_ids))
+		return 0;
 
 	/*
 	 * Yell if perf reports support for a fixed counter but perf doesn't
-- 
2.54.0