From 541670e49812b5b07079cc86367247402ace331a Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@ost.ch>
Date: Tue, 17 Mar 2026 14:19:02 +0100
Subject: x86_64/memory: finish HHDM-based mapper

---
 arch/x86_64/src/memory/higher_half_mapper.cpp | 104 ++++++++++++++++++++++++--
 1 file changed, 97 insertions(+), 7 deletions(-)

(limited to 'arch/x86_64/src/memory')

diff --git a/arch/x86_64/src/memory/higher_half_mapper.cpp b/arch/x86_64/src/memory/higher_half_mapper.cpp
index 9fe3c89..abb54a3 100644
--- a/arch/x86_64/src/memory/higher_half_mapper.cpp
+++ b/arch/x86_64/src/memory/higher_half_mapper.cpp
@@ -1,29 +1,119 @@
 #include "arch/memory/higher_half_mapper.hpp"
 
 #include "kapi/memory.hpp"
+#include "kapi/system.hpp"
 
+#include "arch/memory/page_table.hpp"
+#include "arch/memory/page_utilities.hpp"
+
+#include <algorithm>
+#include <array>
 #include <cstddef>
+#include <memory>
+#include <ranges>
+#include <utility>
 
 namespace arch::memory
 {
 
+  higher_half_mapper::higher_half_mapper(page_table * root)
+      : m_root{root}
+  {}
+
   auto higher_half_mapper::map(kapi::memory::page page, kapi::memory::frame frame, flags flags) -> std::byte *
   {
-    static_cast<void>(page);
-    static_cast<void>(frame);
-    static_cast<void>(flags);
-    return nullptr;
+    auto table = get_or_create_page_table(page);
+    if (!table)
+    {
+      return nullptr;
+    }
+
+    auto const index = pml_index(1, page);
+    auto & entry = (*table)[index];
+
+    if (entry.present())
+    {
+      kapi::system::panic("[x86_64:MEM] Tried to map a page that is already mapped!");
+    }
+
+    entry.frame(frame, to_table_flags(flags) | page_table::entry::flags::present);
+
+    return static_cast<std::byte *>(page.start_address());
   }
 
   auto higher_half_mapper::unmap(kapi::memory::page page) -> void
   {
-    static_cast<void>(page);
+    if (!try_unmap(page))
+    {
+      kapi::system::panic("[x86_64:MEM] Tried to unmap a page that is not mapped!");
+    }
   }
 
   auto higher_half_mapper::try_unmap(kapi::memory::page page) noexcept -> bool
   {
-    static_cast<void>(page);
-    return false;
+    auto table_path = std::array<std::pair<page_table *, std::size_t>, 4>{};
+    table_path[0] = std::pair{m_root, pml_index(4, page)};
+
+    for (auto level = 4uz; level > 1uz; --level)
+    {
+      auto [table, index] = table_path[4 - level];
+      auto & entry = (*table)[index];
+
+      if (!entry.present())
+      {
+        return false;
+      }
+
+      auto next_table = to_higher_half_pointer<page_table>(entry.frame()->start_address());
+      auto next_index = pml_index(4 - level - 1, page);
+      table_path[4 - level - 1] = std::pair{next_table, next_index};
+    }
+
+    std::ranges::for_each(std::views::reverse(table_path), [previous_was_empty = true](auto & step) mutable {
+      auto [table, index] = step;
+      auto & entry = (*table)[index];
+      auto frame = entry.frame();
+
+      if (previous_was_empty)
+      {
+        entry.clear();
+        previous_was_empty = table->empty();
+        kapi::memory::get_frame_allocator().release(*frame);
+      }
+    });
+
+    return true;
+  }
+
+  auto higher_half_mapper::get_or_create_page_table(kapi::memory::page page) noexcept -> page_table *
+  {
+    auto table = m_root;
+
+    for (auto level = 4uz; level > 1uz; --level)
+    {
+      auto index = pml_index(level, page);
+      auto & entry = (*table)[index];
+
+      if (!entry.present())
+      {
+        auto table_frame = kapi::memory::allocate_frame();
+        if (!table_frame)
+        {
+          return nullptr;
+        }
+
+        auto new_table = to_higher_half_pointer<page_table>(table_frame->start_address());
+        std::construct_at(new_table);
+
+        auto const flags = page_table::entry::flags::present | page_table::entry::flags::writable |
+                           page_table::entry::flags::user_accessible;
+        entry.frame(*table_frame, flags);
+      }
+
+      table = to_higher_half_pointer<page_table>(entry.frame()->start_address());
+    }
+
+    return table;
   }
 
 }  // namespace arch::memory
\ No newline at end of file
-- 
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