KVM: x86: Clear apic tsc-deadline after deadline

Intel SDM 10.5.4.1 says "When the timer generates an interrupt, it disarms
itself and clears the IA32_TSC_DEADLINE MSR".

This patch clears the MSR upon timer interrupt delivery which delivered on
deadline mode.  Since the MSR may be reconfigured while an interrupt is
pending, causing the new value to be overriden, pending timer interrupts are
checked before setting a new deadline.
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/lapic.c

@@ -1352,6 +1352,9 @@ void kvm_set_lapic_tscdeadline_msr(struct kvm_vcpu *vcpu, u64 data)
 		return;
 
 	hrtimer_cancel(&apic->lapic_timer.timer);
+	/* Inject here so clearing tscdeadline won't override new value */
+	if (apic_has_pending_timer(vcpu))
+		kvm_inject_apic_timer_irqs(vcpu);
 	apic->lapic_timer.tscdeadline = data;
 	start_apic_timer(apic);
 }
@@ -1639,6 +1642,8 @@ void kvm_inject_apic_timer_irqs(struct kvm_vcpu *vcpu)
 
 	if (atomic_read(&apic->lapic_timer.pending) > 0) {
 		kvm_apic_local_deliver(apic, APIC_LVTT);
+		if (apic_lvtt_tscdeadline(apic))
+			apic->lapic_timer.tscdeadline = 0;
 		atomic_set(&apic->lapic_timer.pending, 0);
 	}
 }