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

[Thomas Gleixner]

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 at linux.intel.com>
> Reviewed-by: Kai Huang <kai.huang at intel.com>
> Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy at linux.intel.com>

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