1. A method for switching to a spare processor during runtime, the method comprising: determining that execution should be migrated off of an active processor in a processing, system; after determining that execution should be migrated off of the active processor, pausing an operating system (OS) scheduler in the processing system, pausing at least one device in the processing system, and putting the active processor into an idle state; saving state data from writable and non-writable stores in the active processor to at least a store outside of the active processor; starting a spare processor in the processing system; loading the saved state data to the spare processor; reprogramming interrupt routing table logic for the processing system to direct external interrupts to the spare processor; off-lining the active processor; resuming the device; resuming the OS scheduler; and dispatching threads to the spare processor for execution, wherein an internal cache of the active processor is to be flushed prior to the off-lining of the active processor to make data stored in the internal cache visible to a memory mirror module and wherein an operating system (OS) selectively reads a memory range with data that needs to be copied from an outgoing memory module of the active processor to a spare memory module of the spare processor by the memory mirror module.