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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>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Tao Liu <ltao@redhat.com>
Link: https://lore.kernel.org/r/20240614095904.1345461-16-kirill.shutemov@linux.intel.com