linux-kernel - Re: [PATCH AUTOSEL 6.6 02/17] x86/acpi: Ignore invalid x2APIC entries

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Message-ID: <20231206070423.wp7cxxnwfe3lidm3@awork3.anarazel.de>
Date:   Tue, 5 Dec 2023 23:04:23 -0800
From:   Andres Freund <andres@...razel.de>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Zhang Rui <rui.zhang@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>, rafael@...nel.org,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 6.6 02/17] x86/acpi: Ignore invalid x2APIC entries

Hi,

On 2023-11-22 10:31:31 -0500, Sasha Levin wrote:
> From: Zhang Rui <rui.zhang@...el.com>
>
> [ Upstream commit ec9aedb2aa1ab7ac420c00b31f5edc5be15ec167 ]
>
> Currently, the kernel enumerates the possible CPUs by parsing both ACPI
> MADT Local APIC entries and x2APIC entries. So CPUs with "valid" APIC IDs,
> even if they have duplicated APIC IDs in Local APIC and x2APIC, are always
> enumerated.

As just described in
https://lore.kernel.org/all/20231206065850.hs7k554v6wym7gw5@awork3.anarazel.de/
and also previously described by John Sperbeck
https://lore.kernel.org/all/20231122221947.781812-1-jsperbeck@google.com/

this patch causes some machines to "loose" cpus. All but one in my case.


Even if the commit didn't have these unintended consequences, it seems like a
commit like this hardly is -stable material?

- Andres