KVM: x86: latch INITs while in system management mode

Do not process INITs immediately while in system management mode, keep
it instead in apic->pending_events.  Tell userspace if an INIT is
pending when they issue GET_VCPU_EVENTS, and similarly handle the
new field in SET_VCPU_EVENTS.

Note that the same treatment should be done while in VMX non-root mode.
Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/lapic.c

@@ -2057,8 +2057,19 @@ void kvm_apic_accept_events(struct kvm_vcpu *vcpu)
 	if (!kvm_vcpu_has_lapic(vcpu) || !apic->pending_events)
 		return;
 
-	pe = xchg(&apic->pending_events, 0);
+	/*
+	 * INITs are latched while in SMM.  Because an SMM CPU cannot
+	 * be in KVM_MP_STATE_INIT_RECEIVED state, just eat SIPIs
+	 * and delay processing of INIT until the next RSM.
+	 */
+	if (is_smm(vcpu)) {
+		WARN_ON_ONCE(vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED);
+		if (test_bit(KVM_APIC_SIPI, &apic->pending_events))
+			clear_bit(KVM_APIC_SIPI, &apic->pending_events);
+		return;
+	}
 
+	pe = xchg(&apic->pending_events, 0);
 	if (test_bit(KVM_APIC_INIT, &pe)) {
 		kvm_lapic_reset(vcpu, true);
 		kvm_vcpu_reset(vcpu, true);

arch/x86/kvm/x86.c

@@ -5482,6 +5482,9 @@ static void kvm_smm_changed(struct kvm_vcpu *vcpu)
 		if (unlikely(vcpu->arch.smi_pending)) {
 			kvm_make_request(KVM_REQ_SMI, vcpu);
 			vcpu->arch.smi_pending = 0;
+		} else {
+			/* Process a latched INIT, if any.  */
+			kvm_make_request(KVM_REQ_EVENT, vcpu);
 		}
 	}
 }