linux-kernel - [PATCH 2/3] KVM: Check preempted_in_kernel for involuntary preemption

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Message-Id: <1564572438-15518-2-git-send-email-wanpengli@tencent.com>
Date:   Wed, 31 Jul 2019 19:27:17 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: [PATCH 2/3] KVM: Check preempted_in_kernel for involuntary preemption

From: Wanpeng Li <wanpengli@...cent.com>

preempted_in_kernel is updated in preempt_notifier when involuntary preemption 
ocurrs, it can be stale when the voluntarily preempted vCPUs are taken into 
account by kvm_vcpu_on_spin() loop. This patch lets it just check preempted_in_kernel 
for involuntary preemption.

Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
 virt/kvm/kvm_main.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 887f3b0..ed061d8 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2508,7 +2508,8 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me, bool yield_to_kernel_mode)
 				continue;
 			if (swait_active(&vcpu->wq) && !kvm_arch_vcpu_runnable(vcpu))
 				continue;
-			if (yield_to_kernel_mode && !kvm_arch_vcpu_in_kernel(vcpu))
+			if (READ_ONCE(vcpu->preempted) && yield_to_kernel_mode &&
+				!kvm_arch_vcpu_in_kernel(vcpu))
 				continue;
 			if (!kvm_vcpu_eligible_for_directed_yield(vcpu))
 				continue;
@@ -4205,7 +4206,7 @@ static void kvm_sched_in(struct preempt_notifier *pn, int cpu)
 {
 	struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn);
 
-	vcpu->preempted = false;
+	WRITE_ONCE(vcpu->preempted, false);
 	WRITE_ONCE(vcpu->ready, false);
 
 	kvm_arch_sched_in(vcpu, cpu);
@@ -4219,7 +4220,7 @@ static void kvm_sched_out(struct preempt_notifier *pn,
 	struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn);
 
 	if (current->state == TASK_RUNNING) {
-		vcpu->preempted = true;
+		WRITE_ONCE(vcpu->preempted, true);
 		WRITE_ONCE(vcpu->ready, true);
 	}
 	kvm_arch_vcpu_put(vcpu);
-- 
2.7.4