MADT / APIC
The Multiple APIC (Advanced Programmable Interrupt Controller) Description Table
This table is used for the ACPI Parking Protocol. It is a protocol that allows parked CPU cores to be unparked. The parked state doesn't allow the CPU cores to execute any code, they are "disabled".
The grate-driver/linux GitHub repository contains a working arm32 version of the ACPI Parking Protocol (Link points to the source file). It allows the usage of SMP on the Surface RT and on other arm32 Windows RT devices. (When you boot Linux from UEFI; not used in APX mode).
The following table describes the MADT entries of the 4 CPU cores. The ACPI Parking Protocol only requires to unpark CPU1-3, as CPU0 is already in use.
The MADT table has an entry about the Generic Interrupt Distributor. Here are the contents: