add 4th level page table

3 files changed, 56 insertions, 3 deletions

diff --git a/arch/x86_64/include/arch/memory/paging.hpp b/arch/x86_64/include/arch/memory/paging.hpp
index 16fa476..7b705ac 100644
--- a/arch/x86_64/include/arch/memory/paging.hpp
+++ b/arch/x86_64/include/arch/memory/paging.hpp
@@ -91,6 +91,9 @@ namespace teachos::arch::memory
      */
     auto contains_flags(std::bitset<64U> other) const -> bool;
 
+    std::bitset<64U> flags;  ///< Underlying bitset used to read the flags from. Bits 9 - 11 and 52 - 62 can be freely
+                             ///< used for additional flags by the operating system.
+
   private:
     /**
      * @brief Extracts the physical address from the underlying bitset read from bit index 12 - 51. Is a 52 bit page
@@ -100,9 +103,6 @@ namespace teachos::arch::memory
      * @return Extracted physical address of the next page or of the frame for P1 page tables.
      */
     auto calculate_physical_address() const -> std::size_t;
-
-    std::bitset<64U> flags;  ///< Underlying bitset used to read the flags from. Bits 9 - 11 and 52 - 62 can be freely
-                             ///< used for additional flags by the operating system.
   };
 
   /**
@@ -116,6 +116,25 @@ namespace teachos::arch::memory
     auto zero_entries() -> void;
 
     /**
+     * @brief Find and return the next table address
+     *
+     * The next table address is only valid if the corresponding entry is present
+     * and does not create a huge page
+     *
+     * @param index
+     * @return An optional of the address of the next page table or null
+     */
+    auto next_table_address(std::size_t index) const -> std::optional<std::size_t>;
+
+    /**
+     * @brief Convert the address of a page_table into a page_table
+     *
+     * @param index
+     * @return An optional of the next page table or null
+     */
+    auto next_table(size_t index) const -> std::optional<const page_table *>;
+
+    /**
      * @brief Index operator overload to access specific entries directy
      *
      * @param index
@@ -129,6 +148,7 @@ namespace teachos::arch::memory
 
   private:
     entry entries[PAGE_TABLE_ENTRY_COUNT];
+    page_table const * p4 = reinterpret_cast<page_table *>(0xfffffffffffff000);
   };
 }  // namespace teachos::arch::memory
 
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