Constant nc::types::__PAGE_OFFSET_BASE_L5

pub const __PAGE_OFFSET_BASE_L5: usize = 0xff11000000000000;

Set __PAGE_OFFSET to the most negative possible address + PGDIR_SIZE*17 (pgd slot 273).

The gap is to allow a space for LDT remap for PTI (1 pgd slot) and space for a hypervisor (16 slots). Choosing 16 slots for a hypervisor is arbitrary, but it’s what Xen requires.