KVM: hlt emulation should take in-kernel APIC/PIT timers into account

Timers that fire between guest hlt and vcpu_block's add_wait_queue() are
ignored, possibly resulting in hangs.

Also make sure that atomic_inc and waitqueue_active tests happen in the
specified order, otherwise the following race is open:

CPU0                                        CPU1
                                            if (waitqueue_active(wq))
add_wait_queue()
if (!atomic_read(pit_timer->pending))
    schedule()
                                            atomic_inc(pit_timer->pending)

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

arch/s390/kvm/interrupt.c

@@ -325,6 +325,11 @@ int kvm_cpu_has_interrupt(struct kvm_vcpu *vcpu)
 	return rc;
 }
 
+int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu)
+{
+	return 0;
+}
+
 int kvm_s390_handle_wait(struct kvm_vcpu *vcpu)
 {
 	u64 now, sltime;