Create a memory::init function that initializes a MappedPageTable

src/memory.rs

@@ -1,4 +1,23 @@
-use x86_64::{structures::paging::PageTable, PhysAddr, VirtAddr};
+use x86_64::{
+    structures::paging::{MappedPageTable, MapperAllSizes, PageTable, PhysFrame},
+    PhysAddr, VirtAddr,
+};
+
+/// Initialize a new MappedPageTable.
+///
+/// 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 init(physical_memory_offset: u64) -> impl MapperAllSizes {
+    let level_4_table = active_level_4_table(physical_memory_offset);
+    let phys_to_virt = move |frame: PhysFrame| -> *mut PageTable {
+        let phys = frame.start_address().as_u64();
+        let virt = VirtAddr::new(phys + physical_memory_offset);
+        virt.as_mut_ptr()
+    };
+    MappedPageTable::new(level_4_table, phys_to_virt)
+}
 
 /// Returns a mutable reference to the active level 4 table.
 ///
@@ -6,7 +25,7 @@ use x86_64::{structures::paging::PageTable, PhysAddr, VirtAddr};
 /// 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 {
+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();