Re: [PATCH v2 3/5] KVM: Selftests: Validate more arch-events in pmu_counters_test

Sean Christopherson
2025-09-10T23:51:03Z

On Fri, Jul 18, 2025, Dapeng Mi wrote:
> Clearwater Forest introduces 5 new architectural events (4 topdown
> level 1 metrics events and LBR inserts event). This patch supports
> to validate these 5 newly added events. The detailed info about these
> 5 events can be found in SDM section 21.2.7 "Pre-defined Architectural
> Performance Events".
>
> It becomes unrealistic to traverse all possible combinations of
> unavailable events mask (may need dozens of minutes to finish all
> possible combination validation). So only limit unavailable events mask
> traverse to the first 8 arch-events.

Split these into separate patches. Buring a meaningful change like this in a big
patch that seemingly just adds architectural collateral is pure evil.
> @@ -612,15 +620,19 @@ 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.
> + * To keep the total runtime reasonable, especially after
> + * the total number of arch-events increasing to 13, It's
> + * impossible to test every possible non-zero, non-reserved
> + * bitmap combination. Only test the first 8-bits combination
> + * 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++)
> + int max_events = min(NR_INTEL_ARCH_EVENTS, 8);

Too arbitrary, and worse, bad coverage. And honestly, even iterating over 255
(or 512?) different values is a waste of time. Ha! And test_arch_events() is
buggy, it takes unavailable_mask as u8 instead of a u32. I'll slot in a patch
to fix that.

As for the runtime, I think it's time to throw in the towel in terms of brute
forcing the validation space, and just test a handful of hopefully-interesting
values, e.g.

---
.../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 cfeed0103341..09ad68675576 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,
+ 0xf0f0f0f0u,
+ 0x0f0f0f0fu,
+ 0xaaaaaaaau,
+ 0xa0a0a0a0u,
+ 0x0a0a0a0au,
+ 0x55555555u,
+ 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",
--