Create a memory::active_level_4_table function

src/lib.rs

@@ -3,6 +3,7 @@
 
 pub mod gdt;
 pub mod interrupts;
+pub mod memory;
 pub mod serial;
 pub mod vga_buffer;
 

src/memory.rs

@@ -0,0 +1,19 @@
+use x86_64::structures::paging::PageTable;
+
+/// Returns a mutable reference to the active level 4 table.
+///
+/// This function is unsafe because the caller must guarantee that the
+/// complete physical memory is mapped to virtual memory at the passed
+/// `physical_memory_offset`. Also, this function must be only called once
+/// to avoid aliasing `&mut` references (which is undefined behavior).
+pub unsafe fn active_level_4_table(physical_memory_offset: u64) -> &'static mut PageTable {
+    use x86_64::{registers::control::Cr3, VirtAddr};
+
+    let (level_4_table_frame, _) = Cr3::read();
+
+    let phys = level_4_table_frame.start_address();
+    let virt = VirtAddr::new(phys.as_u64() + physical_memory_offset);
+    let page_table_ptr: *mut PageTable = virt.as_mut_ptr();
+
+    &mut *page_table_ptr // unsafe
+}