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

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Date: Wed, 08 May 2024 23:47:52 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Mario Limonciello <mario.limonciello@....com>, 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")

Mario!

On Thu, May 02 2024 at 05:33, Mario Limonciello wrote:
> On 4/25/2024 16:42, Thomas Gleixner wrote:
>> Right, that's what we saw with the debug patch. The ACPI/MADT table
>> is clearly bonkers. The effect of it is that it pretends that the system
>> has 16 possible CPUs:
>> 
>>      [    0.089381] CPU topo: Allowing 8 present CPUs plus 8 hotplug CPUs
>> 
>> Which in turn changes the sizing of the per CPU data and affects some
>> other details which depend on the number of possible CPUs.
>
> At least this aspect of this I suspect is caused by commit 
> fed8d8773b8ea68ad99d9eee8c8343bef9da2c2c.
>
> If you try reverting that I expect the "hotplug CPUs" disappear.

That does not solve anything.

The topology core already rejects those CPUs and accounts only for 8,
which in turn causes the boot to fail as also demonstrated by limiting
the number of possible CPUs to 8.

There is some other problem with this broken BIOS/ACPI.