On Tue, 6 Nov 2018 19:31:27 +0100 Pierre Morel <pmorel@xxxxxxxxxxxxx> wrote: > On 06/11/2018 18:54, Cornelia Huck wrote: > > On Tue, 6 Nov 2018 17:54:17 +0100 > > Halil Pasic <pasic@xxxxxxxxxxxxx> wrote: > > > >> On Thu, 25 Oct 2018 14:37:45 +0200 > >> Michael Mueller <mimu@xxxxxxxxxxxxx> wrote: > >> > >>> This metric will allow to identify how many vcpus are currently > >>> running for a given kvm in SIE context. Its value is between 0 and > >>> the number of vcpus defined for the kvm guest, but never lager than > >>> the number of cpus available to the KVM host in total. > >>> > >>> This metric is required to decide if the GISA IAM has to be restored > >>> from the kvm arch field of the guest. That will be the case when no > >>> vcpu is in SIE context. (vcpus_in_sie == 0) > >>> > >> > >> Mimu, we just spoke about -- thus a reminder for us, and a FYI for > >> the rest. vcpus_in_sie != 0 does not necessarily mean that FW can > >> deliver GISA interrupts to the guest (and thus we don't have to > >> dispatch a suitable vcpu): if all cpus in SIE mask IO interrupts it > >> does not really matter that they are in SIE. I.e. we should still get > >> alerted and try to dispatch an eligible vcpu. > > If I understood well, I do not agree. > If all the vCPU have ISC masked in CR6 we do not need to dispatch the > vCPU, running or not. > If running, > The first vCPU that will load CR6 with at least one bit of the ISC being > one will be scheduled by the firmware. I guess that would also be the case if the vCPU has I/O interrupts masked in its PSW (being scheduled again if it switches on I/O interrupts)? > > We should not set the IAM if a vCPU with interrupt not masked is running > because we will get the alert prior to the guest and loose the benefit > of an interrupt directly sent to the guest. > > The design done here is right. > > > > > So, do we need to restore the IAM as well if all cpus in SIE have I/O > > interrupts masked? Or is it just some dispatching we have to do? > > > > If not running, I think this is the right question. > > We should not restore the IAM and should not dispatch the vCPU. > However I am not sure that dispatching the vCPU causes a problem. > > Restoring the IAM would prevent the GISA to be delivered if another > interrupt arrives. >
