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

[Heiko Carstens <hca@linux.ibm.com>]

> > > +       /* 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).