Function set_trampoline_execution 

pub fn set_trampoline_execution(
    physical: u64,
    executable: bool,
) -> Result<(), &'static str>

Change execution of just the existing 4 KiB identity trampoline page, preserving its cache selector. BSP enables it before SIPI and retires it after every AP has left it. APs invalidate their TLB at the boot barrier.