linux-kernel - [PATCH 4.19 094/105] KVM: lapic: Busy wait for timer to expire when using hv

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Date:   Mon, 20 May 2019 14:14:40 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Wanpeng Li <wanpengli@...cent.com>,
        Liran Alon <liran.alon@...cle.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 4.19 094/105] KVM: lapic: Busy wait for timer to expire when using hv_timer

From: Sean Christopherson <sean.j.christopherson@...el.com>

commit ee66e453db13d4837a0dcf9d43efa7a88603161b upstream.

...now that VMX's preemption timer, i.e. the hv_timer, also adjusts its
programmed time based on lapic_timer_advance_ns.  Without the delay, a
guest can see a timer interrupt arrive before the requested time when
KVM is using the hv_timer to emulate the guest's interrupt.

Fixes: c5ce8235cffa0 ("KVM: VMX: Optimize tscdeadline timer latency")
Cc: <stable@...r.kernel.org>
Cc: Wanpeng Li <wanpengli@...cent.com>
Reviewed-by: Liran Alon <liran.alon@...cle.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/kvm/lapic.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1449,7 +1449,7 @@ static void apic_timer_expired(struct kv
 	if (swait_active(q))
 		swake_up_one(q);
 
-	if (apic_lvtt_tscdeadline(apic))
+	if (apic_lvtt_tscdeadline(apic) || ktimer->hv_timer_in_use)
 		ktimer->expired_tscdeadline = ktimer->tscdeadline;
 }