linux-kernel - [kvm-unit-tests PATCH] x86: pmu: Test perfctr overflow after WRMSR on a running counter

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Message-Id: <20200221224133.103377-1-ehankland@google.com>
Date:   Fri, 21 Feb 2020 14:41:33 -0800
From:   Eric Hankland <ehankland@...gle.com>
To:     Jim Mattson <jmattson@...gle.com>, Peter Shier <pshier@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Eric Hankland <ehankland@...gle.com>
Subject: [kvm-unit-tests PATCH] x86: pmu: Test perfctr overflow after WRMSR on
 a running counter

Ensure that a WRMSR on a running counter will correctly update when the
counter should overflow (similar to the existing overflow test case but
with the counter being written to while it is running).

Signed-off-by: Eric Hankland <ehankland@...gle.com>
---
 x86/pmu.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/x86/pmu.c b/x86/pmu.c
index c8096b8..f45621a 100644
--- a/x86/pmu.c
+++ b/x86/pmu.c
@@ -422,17 +422,34 @@ static void check_rdpmc(void)
 
 static void check_running_counter_wrmsr(void)
 {
+	uint64_t status;
 	pmu_counter_t evt = {
 		.ctr = MSR_IA32_PERFCTR0,
 		.config = EVNTSEL_OS | EVNTSEL_USR | gp_events[1].unit_sel,
 		.count = 0,
 	};
 
+	report_prefix_push("running counter wrmsr");
+
 	start_event(&evt);
 	loop();
 	wrmsr(MSR_IA32_PERFCTR0, 0);
 	stop_event(&evt);
-	report(evt.count < gp_events[1].min, "running counter wrmsr");
+	report(evt.count < gp_events[1].min, "cntr");
+
+	/* clear status before overflow test */
+	wrmsr(MSR_CORE_PERF_GLOBAL_OVF_CTRL,
+	      rdmsr(MSR_CORE_PERF_GLOBAL_STATUS));
+
+	evt.count = 0;
+	start_event(&evt);
+	wrmsr(MSR_IA32_PERFCTR0, -1);
+	loop();
+	stop_event(&evt);
+	status = rdmsr(MSR_CORE_PERF_GLOBAL_STATUS);
+	report(status & 1, "status");
+
+	report_prefix_pop();
 }
 
 int main(int ac, char **av)