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

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Message-ID: <a9111a91-33e4-4f07-96c8-5d724a8429f1@amd.com>
Date: Thu, 13 Nov 2025 08:55:29 -0600
From: Mario Limonciello <mario.limonciello@....com>
To: Borislav Petkov <bp@...en8.de>
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 11/13/25 8:34 AM, Borislav Petkov wrote:
> 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.
> 

OK.