memory::paging: add a struct to own the P4 table, make Page Clone+Copy

src/arch/x86_64/memory/paging/mod.rs

@@ -3,11 +3,16 @@
 //! Extremely ripped off from Phil Oppermann's tutorials, because I don't feel like writing
 //! a paging system off the top of my head today.
 
+use core::ptr::Unique;
 use super::PAGE_SIZE;
+use super::{Frame, FrameAllocator};
 
 mod entry;
 mod table;
 
+use self::entry::*;
+use self::table::{Table, Level4};
+
 /// Upper bound on entries per page table
 const ENTRY_COUNT: usize = 512;
 
@@ -15,7 +20,23 @@ const ENTRY_COUNT: usize = 512;
 pub type PhysicalAddress = usize;
 pub type VirtualAddress = usize;
 
-/// A representation of a virtual page
+/// Owns the top-level active page table (P4).
+pub struct ActivePageTable {
+    p4: Unique<Table<Level4>>,
+}
+
+impl ActivePageTable {
+    /// There **must** be ***only one*** ActivePageTable instance.
+    /// Since we cannot guarantee this trivially, the constructor is unsafe.
+    pub unsafe fn new() -> ActivePageTable {
+        ActivePageTable {
+            p4: Unique::new(table::P4),
+        }
+    }
+}
+
+/// A representation of a virtual page.
+#[derive(Clone, Copy, Debug)]
 pub struct Page {
     index: usize,
 }