Am Tue, 11 Sep 2018 09:52:58 +0200
schrieb Olaf Hering <olaf@aepfle.de>:

> As Jürgen suggested in another mail, Xen should probably disable hotplugging
> for cpu#0 in the generic setup code. Then cpu_is_hotpluggable(cpu) would
> do the right thing.

The relevant code is all private to arch/x86/kernel/topology.c.
There is no way to set .hotpluggable prior to register_cpu.
I guess you need to work that out with the x86 maintainers.

Olaf