linux-kernel - Re: [PATCHv7 13/16] x86/acpi: Do not attempt to bring up secondary CPUs in kexec case

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Date: Fri, 23 Feb 2024 11:28:28 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Ingo Molnar
 <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen
 <dave.hansen@...ux.intel.com>, x86@...nel.org
Cc: "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, "Kirill A. Shutemov"
 <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCHv7 13/16] x86/acpi: Do not attempt to bring up secondary
 CPUs in kexec case

On Mon, Feb 12 2024 at 12:44, Kirill A. Shutemov wrote:
> ACPI MADT doesn't allow to offline a CPU after it was onlined. This
> limits kexec: the second kernel won't be able to use more than one CPU.
>
> To prevent a kexec kernel from onlining secondary CPUs invalidate the
> mailbox address in the ACPI MADT wakeup structure which prevents a
> kexec kernel to use it.
>
> This is safe as the booting kernel has the mailbox address cached
> already and acpi_wakeup_cpu() uses the cached value to bring up the
> secondary CPUs.
>
> Note: This is a Linux specific convention and not covered by the
>       ACPI specification.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Reviewed-by: Kai Huang <kai.huang@...el.com>
> Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>