Re: [PATCH v7 1/1] s390x: KVM: guest support for topology function

Heiko Carstens
2022-02-18T15:10:42Z

> > > +       /* The real CPU backing up the vCPU moved to another socket
> > > */
> > > +       if (topology_physical_package_id(vcpu->cpu) !=
> > > +           topology_physical_package_id(vcpu->arch.prev_cpu))
> > > +               return true;
> >
> > Why is it OK to look just at the physical package ID here? What if the
> > vcpu for example moves to a different book, which has a core with the
> > same physical package ID?
> >
>
> You are right, we should look at the drawer and book id too.
> Something like that I think:
>
> if ((topology_physical_package_id(vcpu->cpu) !=
> topology_physical_package_id(vcpu->arch.prev_cpu)) ||
> (topology_book_id(vcpu->cpu) !=
> topology_book_id(vcpu->arch.prev_cpu)) ||
> (topology_drawer_id(vcpu->cpu) !=
> topology_drawer_id(vcpu->arch.prev_cpu)))
> return true;

You only need to check if prev_cpu is present in topology_core_cpumask(cpu).