From 45b5817a3603ea4d6caa2f88f909feb4ce767b1e Mon Sep 17 00:00:00 2001
From: Drew Galbraith <dgalbraith33@gmail.com>
Date: Thu, 18 May 2023 01:18:51 -0700
Subject: [PATCH] Recursively map the PML4

---
 zion/CMakeLists.txt         |  1 +
 zion/memory/paging_util.cpp | 20 ++++++++++++++++++++
 zion/memory/paging_util.h   |  6 ++++++
 zion/zion.cpp               |  2 ++
 4 files changed, 29 insertions(+)
 create mode 100644 zion/memory/paging_util.cpp
 create mode 100644 zion/memory/paging_util.h

diff --git a/zion/CMakeLists.txt b/zion/CMakeLists.txt
index d72a17f..d1de879 100644
--- a/zion/CMakeLists.txt
+++ b/zion/CMakeLists.txt
@@ -5,6 +5,7 @@ add_executable(zion
   debug/debug.cpp
   interrupt/interrupt.cpp
   interrupt/interrupt_enter.s
+  memory/paging_util.cpp
   zion.cpp)
 
 target_include_directories(zion
diff --git a/zion/memory/paging_util.cpp b/zion/memory/paging_util.cpp
new file mode 100644
index 0000000..48b74af
--- /dev/null
+++ b/zion/memory/paging_util.cpp
@@ -0,0 +1,20 @@
+#include "memory/paging_util.h"
+
+#include "boot/boot_info.h"
+
+#define PRESENT_BIT 0x1
+#define READ_WRITE_BIT 0x2
+
+void InitPaging() {
+  uint64_t pml4_addr = 0;
+  asm volatile("mov %%cr3, %0;" : "=r"(pml4_addr));
+  InitializePml4(pml4_addr);
+}
+
+void InitializePml4(uint64_t pml4_physical_addr) {
+  uint64_t* pml4_virtual = reinterpret_cast<uint64_t*>(
+      boot::GetHigherHalfDirectMap() + pml4_physical_addr);
+
+  uint64_t recursive_entry = pml4_physical_addr | PRESENT_BIT | READ_WRITE_BIT;
+  pml4_virtual[0x1FE] = recursive_entry;
+}
diff --git a/zion/memory/paging_util.h b/zion/memory/paging_util.h
new file mode 100644
index 0000000..75644d0
--- /dev/null
+++ b/zion/memory/paging_util.h
@@ -0,0 +1,6 @@
+#pragma once
+
+#include <stdint.h>
+
+void InitPaging();
+void InitializePml4(uint64_t pml4_physical_addr);
diff --git a/zion/zion.cpp b/zion/zion.cpp
index 12ffa8b..9821400 100644
--- a/zion/zion.cpp
+++ b/zion/zion.cpp
@@ -5,10 +5,12 @@
 #include "common/gdt.h"
 #include "debug/debug.h"
 #include "interrupt/interrupt.h"
+#include "memory/paging_util.h"
 
 extern "C" void zion() {
   InitGdt();
   InitIdt();
+  InitPaging();
 
   const limine_memmap_response& resp = boot::GetMemoryMap();
   dbgln("Base,Length,Type");