linux-kernel - [PATCH] KVM: LAPIC: Accurately guarantee busy wait for timer to expire when using hv

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Message-Id: <1619608082-4187-1-git-send-email-wanpengli@tencent.com>
Date:   Wed, 28 Apr 2021 19:08:02 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: [PATCH] KVM: LAPIC: Accurately guarantee busy wait for timer to expire when using hv_timer

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

Commit ee66e453db13d (KVM: lapic: Busy wait for timer to expire when 
using hv_timer) tries to set ktime->expired_tscdeadline by checking 
ktime->hv_timer_in_use since lapic timer oneshot/periodic modes which 
are emulated by vmx preemption timer also get advanced, they leverage 
the same vmx preemption timer logic with tsc-deadline mode. However, 
ktime->hv_timer_in_use is cleared before apic_timer_expired() handling, 
let's delay this clearing in preemption-disabled region.

Fixes: ee66e453db13d (KVM: lapic: Busy wait for timer to expire when using hv_timer)
Cc: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
 arch/x86/kvm/lapic.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 152591f..c0ebef5 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1913,8 +1913,8 @@ void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu)
 	if (!apic->lapic_timer.hv_timer_in_use)
 		goto out;
 	WARN_ON(rcuwait_active(&vcpu->wait));
-	cancel_hv_timer(apic);
 	apic_timer_expired(apic, false);
+	cancel_hv_timer(apic);
 
 	if (apic_lvtt_period(apic) && apic->lapic_timer.period) {
 		advance_periodic_target_expiration(apic);
-- 
2.7.4