linux-kernel - Re: [PATCHv10 04/18] cpu/hotplug, x86/acpi: Disable CPU offlining for ACPI MADT wakeup

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Date: Wed, 24 Apr 2024 07:40:26 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 Borislav Petkov <bp@...en8.de>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
 "Rafael J. Wysocki" <rafael@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>,
 Adrian Hunter <adrian.hunter@...el.com>,
 Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
 Elena Reshetova <elena.reshetova@...el.com>,
 Jun Nakajima <jun.nakajima@...el.com>,
 Rick Edgecombe <rick.p.edgecombe@...el.com>,
 Tom Lendacky <thomas.lendacky@....com>, "Kalra, Ashish"
 <ashish.kalra@....com>, Sean Christopherson <seanjc@...gle.com>,
 "Huang, Kai" <kai.huang@...el.com>, Baoquan He <bhe@...hat.com>,
 kexec@...ts.infradead.org, linux-coco@...ts.linux.dev,
 linux-kernel@...r.kernel.org, Tao Liu <ltao@...hat.com>
Subject: Re: [PATCHv10 04/18] cpu/hotplug, x86/acpi: Disable CPU offlining for
 ACPI MADT wakeup

On 4/24/24 07:35, Kirill A. Shutemov wrote:
>> Also, does this need to go to stable although it is kinda big for
>> stable. If stable, do we need a smaller fix first which is backportable?
> Correct me, if I am wrong, but I believe TDX guest is the only user of
> ACPI MADT wake up method. At least it was added into kernel for TDX guest.
> So it wouldn't fix anything user-visible. It might affect a future
> platform that uses this wake up method, but it is a guessing game.

Yeah, the MADT wakeup is pretty funky, highly TDX specific, and not in
use or planned to be _put_ into use anywhere else.  The X86S "fix" for
running in real mode does something else entirely:

	https://cdrdv2.intel.com/v1/dl/getContent/776648