On Tue, 8 Jan 2019 14:36:13 +0100 Halil Pasic <pasic@xxxxxxxxxxxxx> wrote: > On Tue, 8 Jan 2019 11:34:44 +0100 > Cornelia Huck <cohuck@xxxxxxxxxx> wrote: > > > > >> > > > >>> + spin_unlock(&kvm->arch.iam_ref_lock); > > > >>> + > > > >>> + return gib->nisc; > > > >>> +} > > > >>> +EXPORT_SYMBOL_GPL(kvm_s390_gisc_register); > > > >>> + > > > >>> +int kvm_s390_gisc_unregister(struct kvm *kvm, u32 gisc) > > > >>> +{ > > > >>> + int rc = 0; > > > >>> + > > > >>> + if (!kvm->arch.gib_in_use) > > > >>> + return -ENODEV; > > > >>> + if (gisc > MAX_ISC) > > > >>> + return -ERANGE; > > > >>> + > > > >>> + spin_lock(&kvm->arch.iam_ref_lock); > > > >>> + if (kvm->arch.iam_ref_count[gisc] == 0) { > > > >>> + rc = -EINVAL; > > > >>> + goto out; > > > >>> + } > > > >>> + kvm->arch.iam_ref_count[gisc]--; > > > >>> + if (kvm->arch.iam_ref_count[gisc] == 0) { > > > >>> + kvm->arch.iam &= ~(0x80 >> gisc); > > > >>> + set_iam(kvm->arch.gisa, kvm->arch.iam); > > > > > > > > Any chance of this function failing here? If yes, would there be any > > > > implications? > > > > > > It is the same here. > > > > I'm not sure that I follow: This is the reverse operation > > (unregistering the gisc). Can we rely on get_ipm() to do any fixup > > later? Is that a problem for the caller? > > IMHO gib alerts are all about not loosing initiative. I.e. avoiding > substantially delayed delivery of interrupts due to vCPUs in wait > state. > > Thus we must avoid letting go before setting up stuff (gisa.iam under > consideration of gisa ipm, gisa.next_alert, and gib.alert_list_origin) > so that we can react on the next interrupt (if necessary). > > On the other hand, getting more gisa alerts than necessary is not > fatal -- better avoided if not too much hassle of course. Yes, unless the caller does not expect any more alerts after unregistering (I guess that's what you're saying?) > > Bottom line is, while it may be critical that the IAM changes implied > by register take place immediately, unregister is a different story. It does feel a bit weird, though. But maybe I just have trouble grasping the design :/