linux-kernel - [kvm-unit-tests patch 3/5] x86/pmu: Fix incorrect masking of fixed counters

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Message-ID: <20250712174915.196103-4-dapeng1.mi@linux.intel.com>
Date: Sat, 12 Jul 2025 17:49:13 +0000
From: Dapeng Mi <dapeng1.mi@...ux.intel.com>
To: Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Jim Mattson <jmattson@...gle.com>,
	Mingwei Zhang <mizhang@...gle.com>,
	Zide Chen <zide.chen@...el.com>,
	Das Sandipan <Sandipan.Das@....com>,
	Shukla Manali <Manali.Shukla@....com>,
	Yi Lai <yi1.lai@...el.com>,
	Dapeng Mi <dapeng1.mi@...el.com>,
	dongsheng <dongsheng.x.zhang@...el.com>,
	Dapeng Mi <dapeng1.mi@...ux.intel.com>
Subject: [kvm-unit-tests patch 3/5] x86/pmu: Fix incorrect masking of fixed counters

From: dongsheng <dongsheng.x.zhang@...el.com>

The current implementation mistakenly limits the width of fixed counters
to the width of GP counters. Corrects the logic to ensure fixed counters
are properly masked according to their own width.

Opportunistically refine the GP counter bitwidth processing code.

Signed-off-by: dongsheng <dongsheng.x.zhang@...el.com>
Co-developed-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Signed-off-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Tested-by: Yi Lai <yi1.lai@...el.com>
---
 x86/pmu.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/x86/pmu.c b/x86/pmu.c
index 04946d10..44c728a5 100644
--- a/x86/pmu.c
+++ b/x86/pmu.c
@@ -556,18 +556,16 @@ static void check_counter_overflow(void)
 		int idx;
 
 		cnt.count = overflow_preset;
-		if (pmu_use_full_writes())
-			cnt.count &= (1ull << pmu.gp_counter_width) - 1;
-
 		if (i == pmu.nr_gp_counters) {
 			if (!pmu.is_intel)
 				break;
 
 			cnt.ctr = fixed_events[0].unit_sel;
-			cnt.count = measure_for_overflow(&cnt);
-			cnt.count &= (1ull << pmu.gp_counter_width) - 1;
+			cnt.count &= (1ull << pmu.fixed_counter_width) - 1;
 		} else {
 			cnt.ctr = MSR_GP_COUNTERx(i);
+			if (pmu_use_full_writes())
+				cnt.count &= (1ull << pmu.gp_counter_width) - 1;
 		}
 
 		if (i % 2)
-- 
2.43.0