On Tue, 2020-10-13 at 12:46 +0200, Thomas Gleixner wrote:
> And after becoming more awake, that wont work anyway because there is
> more than one IR domain, so there is no way to return an error "You
> forgot to register" obviously.
> 
> But the APIC id (32768) valid check is also broken because IR can be
> enabled even without X2APIC.

Nope, it's perfectly OK to allow HPET and I/OAPIC to be parented in the
x86_vector_domain in that case, regardless of IR.

The *actual* criterion for x86_vector_select() returning zero to say 
"don't use me" is "could there be CPUs in the system which can't be
reached through x86_vector_msi_compose_msg()?". It's not really about
IR at all.

The apic_id_valid(32768) check is checking precisely the right thing.