KVM: lapic: reorganize start_hv_timer

There are many cases in which the hv timer must be canceled.  Split out
a new function to avoid duplication.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/lapic.c

@@ -1501,24 +1501,38 @@ static void cancel_hv_timer(struct kvm_lapic *apic)
 	preempt_enable();
 }
 
-static bool start_hv_timer(struct kvm_lapic *apic)
+static bool __start_hv_timer(struct kvm_lapic *apic)
 {
-	u64 tscdeadline = apic->lapic_timer.tscdeadline;
+	struct kvm_timer *ktimer = &apic->lapic_timer;
+	int r;
 
-	if ((atomic_read(&apic->lapic_timer.pending) &&
-		!apic_lvtt_period(apic)) ||
-		kvm_x86_ops->set_hv_timer(apic->vcpu, tscdeadline)) {
-		if (apic->lapic_timer.hv_timer_in_use)
-			cancel_hv_timer(apic);
-	} else {
-		apic->lapic_timer.hv_timer_in_use = true;
-		hrtimer_cancel(&apic->lapic_timer.timer);
+	if (!apic_lvtt_period(apic) && atomic_read(&ktimer->pending))
+		return false;
+
+	r = kvm_x86_ops->set_hv_timer(apic->vcpu, ktimer->tscdeadline);
+	if (r < 0)
+		return false;
+
+	ktimer->hv_timer_in_use = true;
+	hrtimer_cancel(&ktimer->timer);
 
-		/* In case the sw timer triggered in the window */
-		if (atomic_read(&apic->lapic_timer.pending) &&
-			!apic_lvtt_period(apic))
+	/*
+	 * Also recheck ktimer->pending, in case the sw timer triggered in
+	 * the window.  For periodic timer, leave the hv timer running for
+	 * simplicity, and the deadline will be recomputed on the next vmexit.
+	 */
+	if (!apic_lvtt_period(apic) && atomic_read(&ktimer->pending))
+		return false;
+	return true;
+}
+
+static bool start_hv_timer(struct kvm_lapic *apic)
+{
+	if (!__start_hv_timer(apic)) {
+		if (apic->lapic_timer.hv_timer_in_use)
 			cancel_hv_timer(apic);
 	}
+
 	trace_kvm_hv_timer_state(apic->vcpu->vcpu_id,
 			apic->lapic_timer.hv_timer_in_use);
 	return apic->lapic_timer.hv_timer_in_use;