From 0c4fd9eaed4a71975879aa83cd2da4b6266a64b5 Mon Sep 17 00:00:00 2001
From: Fabian Imhof <fabian.imhof@ost.ch>
Date: Tue, 15 Oct 2024 15:48:43 +0000
Subject: add 4th level page table

---
 arch/x86_64/src/boot/boot.s       |  6 ++++++
 arch/x86_64/src/memory/paging.cpp | 27 +++++++++++++++++++++++++++
 2 files changed, 33 insertions(+)

(limited to 'arch/x86_64/src')

diff --git a/arch/x86_64/src/boot/boot.s b/arch/x86_64/src/boot/boot.s
index 0c21c66..29ac58d 100644
--- a/arch/x86_64/src/boot/boot.s
+++ b/arch/x86_64/src/boot/boot.s
@@ -264,6 +264,12 @@ enable_paging:
     mov $page_map_level_4, %eax
     mov %eax, %cr3
 
+    /* Map the P4 table recursively */
+    mov $page_map_level_4, %eax
+    or 0b11, %eax
+    // TODO: WHY THIS THROW ERROR?
+    mov %eax, [$page_map_level_4 + 511 * 8]
+
     /* Enable Physical Address Extension */
     mov %cr4, %eax
     or $(1 << 5), %eax
diff --git a/arch/x86_64/src/memory/paging.cpp b/arch/x86_64/src/memory/paging.cpp
index 445c796..61d9d0f 100644
--- a/arch/x86_64/src/memory/paging.cpp
+++ b/arch/x86_64/src/memory/paging.cpp
@@ -50,4 +50,31 @@ namespace teachos::arch::memory
       entry->set_unused();
     }
   }
+
+  auto page_table::next_table_address(std::size_t index) const -> std::optional<std::size_t>
+  {
+    auto entry = entries[index];
+
+    if (entry.contains_flags(entry.PRESENT) && !entry.contains_flags(entry.HUGE_PAGE))
+    {
+      std::size_t table_address = reinterpret_cast<std::size_t>(this);
+      return (table_address << 9) | (index << 12);
+    }
+    else
+    {
+      return std::nullopt;
+    }
+  }
+
+  auto page_table::next_table(size_t index) const -> std::optional<const page_table *>
+  {
+    auto address = next_table_address(index);
+
+    if (address.has_value())
+    {
+      return reinterpret_cast<const page_table *>(*address);
+    }
+
+    return std::nullopt;
+  }
 }  // namespace teachos::arch::memory
-- 
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