From c6dd37dcc503fae00b76298258eb706ff64ff40d Mon Sep 17 00:00:00 2001
From: Philipp Oppermann <dev@phil-opp.com>
Date: Tue, 18 Apr 2017 12:35:19 +0200
Subject: [PATCH] Turn page of old P4 into guard page

---
 src/memory/paging/mod.rs | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/memory/paging/mod.rs b/src/memory/paging/mod.rs
index 73b0d531..06843620 100644
--- a/src/memory/paging/mod.rs
+++ b/src/memory/paging/mod.rs
@@ -196,4 +196,11 @@ pub fn remap_the_kernel<A>(allocator: &mut A, boot_info: &BootInformation)
 
     let old_table = active_table.switch(new_table);
     println!("NEW TABLE!!!");
+
+    // turn the old p4 page into a guard page
+    let old_p4_page = Page::containing_address(
+      old_table.p4_frame.start_address()
+    );
+    active_table.unmap(old_p4_page, allocator);
+    println!("guard page at {:#x}", old_p4_page.start_address());
 }