KVM: LAPIC: Guarantee the timer is in tsc-deadline mode when setting

Check apic_lvtt_tscdeadline() mode directly instead of apic_lvtt_oneshot()
and apic_lvtt_period() to guarantee the timer is in tsc-deadline mode when
wrmsr MSR_IA32_TSCDEADLINE.

Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Message-Id: <1599731444-3525-3-git-send-email-wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/lapic.c

@@ -2198,8 +2198,7 @@ void kvm_set_lapic_tscdeadline_msr(struct kvm_vcpu *vcpu, u64 data)
 {
 	struct kvm_lapic *apic = vcpu->arch.apic;
 
-	if (!kvm_apic_present(vcpu) || apic_lvtt_oneshot(apic) ||
-			apic_lvtt_period(apic))
+	if (!kvm_apic_present(vcpu) || !apic_lvtt_tscdeadline(apic))
 		return;
 
 	hrtimer_cancel(&apic->lapic_timer.timer);