pub struct Cr3;
Contains the physical address of the level 4 page table.
Read the current P4 table address from the CR3 register along with PCID.
The correct functioning of this requires CR4.PCIDE = 1.
Write a new P4 table address into the CR3 register.
Changing the level 4 page table is unsafe, because it’s possible to violate memory safety by changing the page mapping.