linux-kernel - Re: [PATCH] x86/acpi/boot: Correct acpi_is_processor

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Message-ID: <20251113143408.GCaRXsYM8aVHLN3zSj@fat_crate.local>
Date: Thu, 13 Nov 2025 15:34:08 +0100
From: Borislav Petkov <bp@...en8.de>
To: Mario Limonciello <mario.limonciello@....com>
Cc: Yazen Ghannam <yazen.ghannam@....com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, Michal Pecio <michal.pecio@...il.com>,
	Eric DeVolder <eric.devolder@...cle.com>
Subject: Re: [PATCH] x86/acpi/boot: Correct acpi_is_processor_usable() check
 again

On Thu, Nov 13, 2025 at 08:30:27AM -0600, Mario Limonciello wrote:
> > +	/*
> > +	 * QEMU expects legacy "Enabled=0" LAPIC entries to be counted as usable
> > +	 * in order to support CPU hotplug in guests.
> > +	 */
> 
> I think it would be good to amend this comment to indicate that the behavior
> of the "enabled bit" changed and that QEMU follows the newer behavior but
> advertises the older version.

This is just there to hint why we're doing this fix to the kernel - i.e.,
try to salvage an already shit situation. Any other deviation from the spec is
not the kernel's problem.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette