linux-kernel - [kvm-unit-tests Patch v3 11/11] x86: pmu: Improve branch misses event verification

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Date: Wed,  3 Jan 2024 11:14:09 +0800
From: Dapeng Mi <dapeng1.mi@...ux.intel.com>
To: Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Jim Mattson <jmattson@...gle.com>
Cc: kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Zhenyu Wang <zhenyuw@...ux.intel.com>,
	Zhang Xiong <xiong.y.zhang@...el.com>,
	Mingwei Zhang <mizhang@...gle.com>,
	Like Xu <like.xu.linux@...il.com>,
	Jinrong Liang <cloudliang@...cent.com>,
	Dapeng Mi <dapeng1.mi@...el.com>,
	Dapeng Mi <dapeng1.mi@...ux.intel.com>
Subject: [kvm-unit-tests Patch v3 11/11] x86: pmu: Improve branch misses event verification

Since IBPB command is already leveraged to force one branch miss
triggering, the lower boundary of branch misses event can be set to 1
instead of 0 on IBPB supported processors. Thus the ambiguity from 0 can
be eliminated.

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

diff --git a/x86/pmu.c b/x86/pmu.c
index c8d4a0dcd362..d5c3fcfaa84c 100644
--- a/x86/pmu.c
+++ b/x86/pmu.c
@@ -172,6 +172,16 @@ static void adjust_events_range(struct pmu_event *gp_events, int branch_idx)
 		gp_events[branch_idx].min = PRECISE_LOOP_BRANCHES;
 		gp_events[branch_idx].max = PRECISE_LOOP_BRANCHES;
 	}
+
+	/*
+	 * If HW supports IBPB, one branch miss is forced to trigger by
+	 * IBPB command. Thus overwrite the lower boundary of branch misses
+	 * event to 1.
+	 */
+	if (has_ibpb()) {
+		/* branch misses event */
+		gp_events[branch_idx + 1].min = 1;
+	}
 }
 
 volatile uint64_t irq_received;
-- 
2.34.1