Re: [tip: x86/urgent] x86/acpi: Ignore invalid x2APIC entries

[Thomas Gleixner]

On Wed, Dec 13 2023 at 07:39, Zhang, Rui wrote:
> Yeah, I agree.
>
> I have posted a patch to do more strict check
> https://lore.kernel.org/all/20231210143925.38722-1-rui.zhang@xxxxxxxxx/
> in case there are some weird cases that LAPIC fails to probe any
> enabled CPU and we also lose the X2APIC cpus.

The return value of acpi_register_lapic() is not really useful.

It returns an error if

  1) the number of registered CPUs reached the limit.
  2) the APIC entry is not enabled

#1: any further X2APIC CPU will be ignored

#2: the return value is bogus as the CPU is accounted for as disabled
    and will eventually lead to #1

    In fact even 'disabled' entries are valid as they can be brought
    in later (that's what "physical" hotplug uses)

The topology evaluation rework gets rid of this return value completely,
so I really don't want to add an dependency on it.

Thanks,

        tglx