KVM: s390: prevent sleep duration underflows in handle_wait()

We sometimes get an underflow for the sleep duration, which most
likely won't result in the short sleep time we wanted.

So let's check for sleep duration underflows and directly continue
to run the guest if we get one.

Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index a845e35f904f48e09f15c32ed4c716f8a91f3763..5744303c1cdeff031fd0fe0093c90e9ab048bbc4 100644 (file)
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -804,14 +804,20 @@ int kvm_s390_handle_wait(struct kvm_vcpu *vcpu)
                return -EOPNOTSUPP; /* disabled wait */
        }
 
-       __set_cpu_idle(vcpu);
        if (!ckc_interrupts_enabled(vcpu)) {
                VCPU_EVENT(vcpu, 3, "%s", "enabled wait w/o timer");
+               __set_cpu_idle(vcpu);
                goto no_timer;
        }
 
        now = get_tod_clock_fast() + vcpu->arch.sie_block->epoch;
        sltime = tod_to_ns(vcpu->arch.sie_block->ckc - now);
+
+       /* underflow */
+       if (vcpu->arch.sie_block->ckc < now)
+               return 0;
+
+       __set_cpu_idle(vcpu);
        hrtimer_start(&vcpu->arch.ckc_timer, ktime_set (0, sltime) , HRTIMER_MODE_REL);
        VCPU_EVENT(vcpu, 5, "enabled wait via clock comparator: %llx ns", sltime);
 no_timer: