KVM: s390: base hrtimer on a monotonic clock

commit 0ac96caf upstream.

The hrtimer that handles the wait with enabled timer interrupts
should not be disturbed by changes of the host time.

This patch changes our hrtimer to be based on a monotonic clock.
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

arch/s390/kvm/kvm-s390.c

@@ -646,7 +646,7 @@ int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu)
 		if (rc)
 			return rc;
 	}
-	hrtimer_init(&vcpu->arch.ckc_timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
+	hrtimer_init(&vcpu->arch.ckc_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 	tasklet_init(&vcpu->arch.tasklet, kvm_s390_tasklet,
 		     (unsigned long) vcpu);
 	vcpu->arch.ckc_timer.function = kvm_s390_idle_wakeup;