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From: Thomas Gleixner <tglx@linutronix.de>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Ingo Molnar
 <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>, Dave Hansen
 <dave.hansen@linux.intel.com>, x86@kernel.org
Cc: "Rafael J. Wysocki" <rafael@kernel.org>, Peter Zijlstra
 <peterz@infradead.org>, Adrian Hunter <adrian.hunter@intel.com>,
 Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>,
 Elena Reshetova <elena.reshetova@intel.com>, Jun Nakajima
 <jun.nakajima@intel.com>, Rick Edgecombe <rick.p.edgecombe@intel.com>, Tom
 Lendacky <thomas.lendacky@amd.com>, "Kalra, Ashish"
 <ashish.kalra@amd.com>, Sean Christopherson <seanjc@google.com>, "Huang,
 Kai" <kai.huang@intel.com>, Baoquan He <bhe@redhat.com>,
 kexec@lists.infradead.org, linux-coco@lists.linux.dev,
 linux-kernel@vger.kernel.org, "Kirill A. Shutemov"
 <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCHv7 13/16] x86/acpi: Do not attempt to bring up secondary
 CPUs in kexec case
In-Reply-To: <20240212104448.2589568-14-kirill.shutemov@linux.intel.com>
References: <20240212104448.2589568-1-kirill.shutemov@linux.intel.com>
 <20240212104448.2589568-14-kirill.shutemov@linux.intel.com>
Date: Fri, 23 Feb 2024 11:28:28 +0100
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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@linux.intel.com>
> Reviewed-by: Kai Huang <kai.huang@intel.com>
> Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

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