From 48e46d13719c0ced708d1f9c03fd10cbac0c7efb Mon Sep 17 00:00:00 2001
From: Joe Richey <joerichey@google.com>
Date: Fri, 28 Feb 2020 20:06:53 -0800
Subject: [PATCH] paging: Make PageTable Memory be owned by Rust

This allows for less complex linking and less `unsafe` code. It also
frees up Rust to place the page tables wherever it wants.
---
 layout.ld     | 10 ----------
 src/main.rs   |  2 +-
 src/paging.rs | 41 ++++++++++++++++-------------------------
 3 files changed, 17 insertions(+), 36 deletions(-)

diff --git a/layout.ld b/layout.ld
index af87cf45..4a6bda51 100644
--- a/layout.ld
+++ b/layout.ld
@@ -13,10 +13,6 @@ ram_max = 2M;
 /* Our stack grows down from ram_max. TODO: Add a guard for stack overflows. */
 stack_size = 64K;
 
-/* Pagetable locations loaded by Firecracker/cloud-hypervisor */
-pml4t = 0x9000;
-pml3t = 0xa000;
-
 SECTIONS
 {
 	/* Mapping in the program headers makes it easier to mmap the whole file. */
@@ -32,12 +28,6 @@ SECTIONS
 
 	firmware_ram_size = . - ram_min;
 
-	/* Memory for identity mapping, keep synced with ADDRESS_SPACE_GIB */
-	address_space_gib = 4;
-	. = ALIGN(4K);
-	pml2ts = .;
-	. += 4K * address_space_gib;
-
 	ASSERT((. <= ram_max - stack_size), "firmware size too big for RAM region")
 
 	/* Match edk2's GccBase.lds DISCARD section */
diff --git a/src/main.rs b/src/main.rs
index 2c6b3766..61c343ab 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#![feature(global_asm)]
+#![feature(global_asm, const_in_array_repeat_expressions)]
 #![cfg_attr(not(test), no_std)]
 #![cfg_attr(not(test), no_main)]
 #![cfg_attr(test, allow(unused_imports, dead_code))]
diff --git a/src/paging.rs b/src/paging.rs
index b10a5fda..3b3124fa 100644
--- a/src/paging.rs
+++ b/src/paging.rs
@@ -5,41 +5,32 @@ use x86_64::{
     PhysAddr,
 };
 
-// Keep in sync with address_space_gib in layout.ld
+// This is the number of GiB we will identity map.
 const ADDRESS_SPACE_GIB: usize = 4;
 
-pub static MANAGER: AtomicRefCell<Manager> = AtomicRefCell::new(Manager);
-pub struct Manager;
-
-extern "C" {
-    static mut pml4t: PageTable;
-    static mut pml3t: PageTable;
-    static mut pml2ts: [PageTable; ADDRESS_SPACE_GIB];
-}
-
-struct Tables<'a> {
-    l4: &'a mut PageTable,
-    l3: &'a mut PageTable,
-    l2s: &'a mut [PageTable],
+pub static MANAGER: AtomicRefCell<Manager> = AtomicRefCell::new(Manager::new());
+pub struct Manager {
+    l4: PageTable,
+    l3: PageTable,
+    l2s: [PageTable; ADDRESS_SPACE_GIB],
 }
 
 impl Manager {
-    fn tables(&mut self) -> Tables {
-        Tables {
-            l4: unsafe { &mut pml4t },
-            l3: unsafe { &mut pml3t },
-            l2s: unsafe { &mut pml2ts },
+    const fn new() -> Self {
+        Manager {
+            l4: PageTable::new(),
+            l3: PageTable::new(),
+            l2s: [PageTable::new(); ADDRESS_SPACE_GIB],
         }
     }
 
     pub fn setup(&mut self) {
         log!("Setting up {} GiB identity mapping", ADDRESS_SPACE_GIB);
-        let Tables { l4, l3, l2s } = self.tables();
 
         let pt_flags = PageTableFlags::PRESENT | PageTableFlags::WRITABLE;
         // Setup Identity map using L2 huge pages
         let mut next_addr = PhysAddr::new(0);
-        for l2 in l2s.iter_mut() {
+        for l2 in self.l2s.iter_mut() {
             for l2e in l2.iter_mut() {
                 l2e.set_addr(next_addr, pt_flags | PageTableFlags::HUGE_PAGE);
                 next_addr += Size2MiB::SIZE;
@@ -47,16 +38,16 @@ impl Manager {
         }
 
         // Point L3 at L2s
-        for (i, l2) in l2s.iter().enumerate() {
-            l3[i].set_addr(phys_addr(l2), pt_flags);
+        for (i, l2) in self.l2s.iter().enumerate() {
+            self.l3[i].set_addr(phys_addr(l2), pt_flags);
         }
 
         // Point L4 at L3
-        l4[0].set_addr(phys_addr(l3), pt_flags);
+        self.l4[0].set_addr(phys_addr(&self.l3), pt_flags);
 
         // Point Cr3 at PML4
         let cr3_flags = Cr3::read().1;
-        let pml4t_frame = PhysFrame::from_start_address(phys_addr(l4)).unwrap();
+        let pml4t_frame = PhysFrame::from_start_address(phys_addr(&self.l4)).unwrap();
         unsafe { Cr3::write(pml4t_frame, cr3_flags) };
         log!("Page tables setup");
     }