linux-kernel - [PATCH v4 3/5] KVM: selftests: Reduce number of "unavailable PMU events" combos tested

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Message-ID: <20250919214648.1585683-4-seanjc@google.com>
Date: Fri, 19 Sep 2025 14:46:46 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Dapeng Mi <dapeng1.mi@...ux.intel.com>, Yi Lai <yi1.lai@...el.com>
Subject: [PATCH v4 3/5] KVM: selftests: Reduce number of "unavailable PMU
 events" combos tested

Reduce the number of combinations of unavailable PMU events masks that are
testing by the PMU counters test.  In reality, testing every possible
combination isn't all that interesting, and certainly not worth the tens
of seconds (or worse, minutes) of runtime.  Fully testing the N^2 space
will be especially problematic in the near future, as 5! new arch events
are on their way.

Use alternating bit patterns (and 0 and -1u) in the hopes that _if_ there
is ever a KVM bug, it's not something horribly convoluted that shows up
only with a super specific pattern/value.

Reported-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Reviewed-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 .../selftests/kvm/x86/pmu_counters_test.c     | 38 +++++++++++--------
 1 file changed, 23 insertions(+), 15 deletions(-)

diff --git a/tools/testing/selftests/kvm/x86/pmu_counters_test.c b/tools/testing/selftests/kvm/x86/pmu_counters_test.c
index 1ef038c4c73f..c6987a9b65bf 100644
--- a/tools/testing/selftests/kvm/x86/pmu_counters_test.c
+++ b/tools/testing/selftests/kvm/x86/pmu_counters_test.c
@@ -577,6 +577,26 @@ static void test_intel_counters(void)
 		PMU_CAP_FW_WRITES,
 	};
 
+	/*
+	 * To keep the total runtime reasonable, test only a handful of select,
+	 * semi-arbitrary values for the mask of unavailable PMU events.  Test
+	 * 0 (all events available) and all ones (no events available) as well
+	 * as alternating bit sequencues, e.g. to detect if KVM is checking the
+	 * wrong bit(s).
+	 */
+	const uint32_t unavailable_masks[] = {
+		0x0,
+		0xffffffffu,
+		0xaaaaaaaau,
+		0x55555555u,
+		0xf0f0f0f0u,
+		0x0f0f0f0fu,
+		0xa0a0a0a0u,
+		0x0a0a0a0au,
+		0x50505050u,
+		0x05050505u,
+	};
+
 	/*
 	 * Test up to PMU v5, which is the current maximum version defined by
 	 * Intel, i.e. is the last version that is guaranteed to be backwards
@@ -614,16 +634,7 @@ static void test_intel_counters(void)
 
 			pr_info("Testing arch events, PMU version %u, perf_caps = %lx\n",
 				v, perf_caps[i]);
-			/*
-			 * To keep the total runtime reasonable, test every
-			 * possible non-zero, non-reserved bitmap combination
-			 * only with the native PMU version and the full bit
-			 * vector length.
-			 */
-			if (v == pmu_version) {
-				for (k = 1; k < (BIT(NR_INTEL_ARCH_EVENTS) - 1); k++)
-					test_arch_events(v, perf_caps[i], NR_INTEL_ARCH_EVENTS, k);
-			}
+
 			/*
 			 * Test single bits for all PMU version and lengths up
 			 * the number of events +1 (to verify KVM doesn't do
@@ -632,11 +643,8 @@ static void test_intel_counters(void)
 			 * ones i.e. all events being available and unavailable.
 			 */
 			for (j = 0; j <= NR_INTEL_ARCH_EVENTS + 1; j++) {
-				test_arch_events(v, perf_caps[i], j, 0);
-				test_arch_events(v, perf_caps[i], j, -1u);
-
-				for (k = 0; k < NR_INTEL_ARCH_EVENTS; k++)
-					test_arch_events(v, perf_caps[i], j, BIT(k));
+				for (k = 1; k < ARRAY_SIZE(unavailable_masks); k++)
+					test_arch_events(v, perf_caps[i], j, unavailable_masks[k]);
 			}
 
 			pr_info("Testing GP counters, PMU version %u, perf_caps = %lx\n",
-- 
2.51.0.470.ga7dc726c21-goog