x86_64/memory: finish HHDM-based mapper

2 files changed, 36 insertions, 4 deletions

diff --git a/arch/x86_64/include/arch/memory/higher_half_mapper.hpp b/arch/x86_64/include/arch/memory/higher_half_mapper.hpp
index 66fb58b..c8df40c 100644
--- a/arch/x86_64/include/arch/memory/higher_half_mapper.hpp
+++ b/arch/x86_64/include/arch/memory/higher_half_mapper.hpp
@@ -2,16 +2,41 @@
 #define TEACHOS_X86_64_HIGHER_HALF_MAPPER_HPP
 
 #include "kapi/memory.hpp"
+
+#include "arch/memory/page_table.hpp"
+
+#include <cstddef>
+
 namespace arch::memory
 {
 
+  //! A simple page mapper making use of a Higher Half Direct Map (HHDM) to access and modify page tables.
   struct higher_half_mapper : kapi::memory::page_mapper
   {
+    //! Construct a new mapper for a hierarchy rooted in the given PML.
+    //!
+    //! @param root The root of the hierarchy to operate on.
+    explicit higher_half_mapper(page_table * root);
+
+    //! @copydoc kapi::memory::page_mapper::map
     auto map(kapi::memory::page page, kapi::memory::frame frame, flags flags) -> std::byte * override;
 
+    //! @copydoc kapi::memory::page_mapper::unmap
     auto unmap(kapi::memory::page page) -> void override;
 
+    //! @copydoc kapi::memory::page_mapper::try_unmap
     auto try_unmap(kapi::memory::page page) noexcept -> bool override;
+
+  private:
+    //! Try to retrieve the the PML1 responsible for mapping this page, creating one if necessary.
+    //!
+    //! This function will create a page table hierarchy leading to the target PML1 if it doesn't exist.
+    //!
+    //! @param page The page to get the PML1 for.
+    //! @return The PML1 that manages the given page, nullptr it the system runs out of memory.
+    auto get_or_create_page_table(kapi::memory::page page) noexcept -> page_table *;
+
+    page_table * m_root;
   };
 
 }  // namespace arch::memory
diff --git a/arch/x86_64/include/arch/memory/page_utilities.hpp b/arch/x86_64/include/arch/memory/page_utilities.hpp
index 8c25af3..c48e74f 100644
--- a/arch/x86_64/include/arch/memory/page_utilities.hpp
+++ b/arch/x86_64/include/arch/memory/page_utilities.hpp
@@ -8,15 +8,22 @@
 namespace arch::memory
 {
 
-  template<std::size_t Level>
-    requires(Level > 0uz && Level < 5uz)
-  constexpr auto pml_index(kapi::memory::page page) noexcept -> std::size_t
+  constexpr auto inline pml_index(std::size_t index, kapi::memory::page page) noexcept -> std::size_t
   {
-    constexpr auto shift_width = (Level - 1) * 9;
+    constexpr auto bits_per_level = 9;
+    auto shift_width = (index - 1) * bits_per_level;
     constexpr auto index_mask = 0x1ffuz;
     return page.number() >> shift_width & index_mask;
   }
 
+  template<typename ValueType = void>
+  [[nodiscard]] constexpr auto to_higher_half_pointer(kapi::memory::physical_address address) -> ValueType *
+  {
+    using namespace kapi::memory;
+    auto const higher_half_address = higher_half_direct_map_base + address.raw();
+    return static_cast<ValueType *>(higher_half_address);
+  }
+
 }  // namespace arch::memory
 
 #endif
\ No newline at end of file