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From: Wanpeng Li <kernellwp@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <seanjc@google.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	Wanpeng Li <wanpengli@tencent.com>
Subject: [PATCH 06/10] KVM: Fix last_boosted_vcpu index assignment bug
Date: Mon, 10 Nov 2025 11:32:27 +0800	[thread overview]
Message-ID: <20251110033232.12538-7-kernellwp@gmail.com> (raw)
In-Reply-To: <20251110033232.12538-1-kernellwp@gmail.com>

From: Wanpeng Li <wanpengli@tencent.com>

From: Wanpeng Li <wanpengli@tencent.com>

In kvm_vcpu_on_spin(), the loop counter 'i' is incorrectly written to
last_boosted_vcpu instead of the actual vCPU index 'idx'. This causes
last_boosted_vcpu to store the loop iteration count rather than the
vCPU index, leading to incorrect round-robin behavior in subsequent
directed yield operations.

Fix this by using 'idx' instead of 'i' in the assignment.

Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
 virt/kvm/kvm_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index b7a0ae2a7b20..cde1eddbaa91 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4026,7 +4026,7 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me, bool yield_to_kernel_mode)
 
 		yielded = kvm_vcpu_yield_to(vcpu);
 		if (yielded > 0) {
-			WRITE_ONCE(kvm->last_boosted_vcpu, i);
+			WRITE_ONCE(kvm->last_boosted_vcpu, idx);
 			break;
 		} else if (yielded < 0 && !--try) {
 			break;
-- 
2.43.0


  parent reply	other threads:[~2025-11-10  3:33 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-11-10  3:32 [PATCH 00/10] sched/kvm: Semantics-aware vCPU scheduling for oversubscribed KVM Wanpeng Li
2025-11-10  3:32 ` [PATCH 01/10] sched: Add vCPU debooster infrastructure Wanpeng Li
2025-11-10  3:32 ` [PATCH 02/10] sched/fair: Add rate-limiting and validation helpers Wanpeng Li
2025-11-12  6:40   ` K Prateek Nayak
2025-11-12  6:44     ` K Prateek Nayak
2025-11-13 13:36       ` Wanpeng Li
2025-11-13 12:00     ` Wanpeng Li
2025-11-10  3:32 ` [PATCH 03/10] sched/fair: Add cgroup LCA finder for hierarchical yield Wanpeng Li
2025-11-12  6:50   ` K Prateek Nayak
2025-11-13  8:59     ` Wanpeng Li
2025-11-10  3:32 ` [PATCH 04/10] sched/fair: Add penalty calculation and application logic Wanpeng Li
2025-11-12  7:25   ` K Prateek Nayak
2025-11-13 13:25     ` Wanpeng Li
2025-11-10  3:32 ` [PATCH 05/10] sched/fair: Wire up yield deboost in yield_to_task_fair() Wanpeng Li
2025-11-10  5:16   ` kernel test robot
2025-11-10  5:16   ` kernel test robot
2025-11-10  3:32 ` Wanpeng Li [this message]
2025-11-21  0:35   ` [PATCH 06/10] KVM: Fix last_boosted_vcpu index assignment bug Sean Christopherson
2025-11-21  0:38     ` Sean Christopherson
2025-11-21 11:46     ` Wanpeng Li
2025-11-10  3:32 ` [PATCH 07/10] KVM: x86: Add IPI tracking infrastructure Wanpeng Li
2025-11-10  3:32 ` [PATCH 08/10] KVM: x86/lapic: Integrate IPI tracking with interrupt delivery Wanpeng Li
2025-11-10  3:32 ` [PATCH 09/10] KVM: Implement IPI-aware directed yield candidate selection Wanpeng Li
2025-11-10  3:39 ` [PATCH 10/10] KVM: Relaxed boost as safety net Wanpeng Li
2025-11-10 12:02 ` [PATCH 00/10] sched/kvm: Semantics-aware vCPU scheduling for oversubscribed KVM Christian Borntraeger
2025-11-12  5:01   ` Wanpeng Li
2025-11-18  8:11     ` Christian Borntraeger
2025-11-18 14:19       ` Wanpeng Li
2025-11-11  6:28 ` K Prateek Nayak
2025-11-12  4:54   ` Wanpeng Li
2025-11-12  6:07     ` K Prateek Nayak
2025-11-13  5:37       ` Wanpeng Li
2025-11-13  4:42     ` K Prateek Nayak
2025-11-13  8:33       ` Wanpeng Li
2025-11-13  9:48         ` K Prateek Nayak
2025-11-13 13:56           ` Wanpeng Li

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