KVM: LAPIC: Introduce limit_periodic_timer_frequency

Extract the logic of limit lapic periodic timer frequency to a new function,
this function will be used by later patches.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: NWanpeng Li <wanpeng.li@hotmail.com>
Signed-off-by: NRadim Krčmář <rkrcmar@redhat.com>

arch/x86/kvm/lapic.c

@@ -1301,6 +1301,27 @@ static void update_divide_count(struct kvm_lapic *apic)
 				   apic->divide_count);
 }
 
+static void limit_periodic_timer_frequency(struct kvm_lapic *apic)
+{
+	/*
+	 * Do not allow the guest to program periodic timers with small
+	 * interval, since the hrtimers are not throttled by the host
+	 * scheduler.
+	 */
+	if (apic_lvtt_period(apic)) {
+		s64 min_period = min_timer_period_us * 1000LL;
+
+		if (apic->lapic_timer.period < min_period) {
+			pr_info_ratelimited(
+			    "kvm: vcpu %i: requested %lld ns "
+			    "lapic timer period limited to %lld ns\n",
+			    apic->vcpu->vcpu_id,
+			    apic->lapic_timer.period, min_period);
+			apic->lapic_timer.period = min_period;
+		}
+	}
+}
+
 static void apic_update_lvtt(struct kvm_lapic *apic)
 {
 	u32 timer_mode = kvm_lapic_get_reg(apic, APIC_LVTT) &
@@ -1445,23 +1466,7 @@ static bool set_target_expiration(struct kvm_lapic *apic)
 	if (!apic->lapic_timer.period)
 		return false;
 
-	/*
-	 * Do not allow the guest to program periodic timers with small
-	 * interval, since the hrtimers are not throttled by the host
-	 * scheduler.
-	 */
-	if (apic_lvtt_period(apic)) {
-		s64 min_period = min_timer_period_us * 1000LL;
-
-		if (apic->lapic_timer.period < min_period) {
-			pr_info_ratelimited(
-			    "kvm: vcpu %i: requested %lld ns "
-			    "lapic timer period limited to %lld ns\n",
-			    apic->vcpu->vcpu_id,
-			    apic->lapic_timer.period, min_period);
-			apic->lapic_timer.period = min_period;
-		}
-	}
+	limit_periodic_timer_frequency(apic);
 
 	apic_debug("%s: bus cycle is %" PRId64 "ns, now 0x%016"
 		   PRIx64 ", "