[kvm-unit-tests patch v6 15/18] x86: pmu: Adjust lower boundary of llc-misses event to 0 for legacy CPUs

[Dapeng Mi]

For these legacy Intel CPUs without clflush/clflushopt support, there is
on way to force to trigger a LLC miss and the measured llc misses is
possible to be 0. Thus adjust the lower boundary of llc-misses event to
0 to avoid possible false positive.

Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
---
 x86/pmu.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/x86/pmu.c b/x86/pmu.c
index c9160423..47b6305d 100644
--- a/x86/pmu.c
+++ b/x86/pmu.c
@@ -82,6 +82,7 @@ struct pmu_event {
 enum {
 	INTEL_INSTRUCTIONS_IDX  = 1,
 	INTEL_REF_CYCLES_IDX	= 2,
+	INTEL_LLC_MISSES_IDX	= 4,
 	INTEL_BRANCHES_IDX	= 5,
 };
 
@@ -892,6 +893,15 @@ int main(int ac, char **av)
 		gp_events_size = sizeof(intel_gp_events)/sizeof(intel_gp_events[0]);
 		instruction_idx = INTEL_INSTRUCTIONS_IDX;
 		branch_idx = INTEL_BRANCHES_IDX;
+
+		/*
+		 * For legacy Intel CPUS without clflush/clflushopt support,
+		 * there is no way to force to trigger a LLC miss, thus set
+		 * the minimum value to 0 to avoid false positives.
+		 */
+		if (!this_cpu_has(X86_FEATURE_CLFLUSH))
+			gp_events[INTEL_LLC_MISSES_IDX].min = 0;
+
 		report_prefix_push("Intel");
 		set_ref_cycle_expectations();
 	} else {
-- 
2.40.1