linux-kernel - Re: Early boot regression from f0551af0213 ("x86/topology: Ignore non-present APIC IDs in a present package")

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Date: Tue, 23 Apr 2024 19:09:51 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Lyude Paul <lyude@...hat.com>, Borislav Petkov <bp@...en8.de>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: Early boot regression from f0551af0213 ("x86/topology: Ignore
 non-present APIC IDs in a present package")

On Sat, Apr 20 2024 at 00:15, Thomas Gleixner wrote:
> Paul!
>
> On Fri, Apr 19 2024 at 13:38, Lyude Paul wrote:
>> Awesome - can confirm the patch does indeed make the machine boot. Full
>> dmesg from boot attached.
>
> Thanks for providing the data.
>
> [    0.089286] CPU topo: APIC ID 0 present 1
> [    0.089294] CPU topo: APIC ID 0 present 0
> [    0.089296] CPU topo: Hot-pluggable APIC ID 0 in present package.
>
> ACPI is really a wonderland.

Second thoughts. I just stared at this some more and I really cannot
figure out why any of this (including the debug patch) makes a
difference or even sense at all.

All the commit you bisected to does is to reject the non-present APIC
IDs, but that's just an accounting thing. Instead of having them
accounted as disabled they are accounted as rejected.

So no. None of this makes any sense at all.