read_cr3_phys

kernel_vmem

Function read_cr3_phys 

Source 
pub unsafe fn read_cr3_phys() -> PhysicalAddress
Expand description

Reads the current value of the CR3 register (the page table base register) and returns the physical address of the top-level page table (PML4).

§Safety

This function is unsafe because it directly accesses a CPU control register. It must only be called in privileged (ring 0) code where paging is active and the CR3 contents are valid. Calling it from user mode or before enabling paging will cause undefined behavior.

§Details

  • On x86-64, CR3 holds the physical base address of the currently active PML4 (Page Map Level 4) table.
  • The low 12 bits of CR3 contain flags (e.g., PCID, reserved bits), so this function masks them out to obtain a 4 KiB-aligned physical address.
  • The returned address represents the root of the current virtual memory hierarchy used for address translation.

§Returns

The 4 KiB-aligned PhysicalAddress of the current PML4 table.

§Example

use kernel_vmem::read_cr3_phys;

// SAFETY: Only call from kernel mode with paging enabled.
let current_pml4 = unsafe { read_cr3_phys() };
println!("Active PML4 base: {:#x}", current_pml4.as_u64());