1 files changed, 71 insertions, 3 deletions

diff --git a/arch/x86_64/src/kapi/memory.cpp b/arch/x86_64/src/kapi/memory.cpp
index 99dcb5c..f34729a 100644
--- a/arch/x86_64/src/kapi/memory.cpp
+++ b/arch/x86_64/src/kapi/memory.cpp
@@ -1,28 +1,34 @@
 #include "kapi/memory.hpp"
 
-#include "kapi/memory/frame.hpp"
-#include "kapi/memory/frame_allocator.hpp"
+#include "kapi/cio.hpp"
 #include "kapi/system.hpp"
 
 #include "x86_64/boot/boot.hpp"
 #include "x86_64/boot/ld.hpp"
 #include "x86_64/cpu/registers.hpp"
+#include "x86_64/memory/mmu.hpp"
+#include "x86_64/memory/page_table.hpp"
+#include "x86_64/memory/paging_root.hpp"
 #include "x86_64/memory/region_allocator.hpp"
 
 #include <multiboot2/information.hpp>
 
 #include <atomic>
+#include <memory>
 #include <span>
 
 namespace teachos::memory
 {
   std::size_t const PLATFORM_FRAME_SIZE{4096};
+  std::size_t const PLATFORM_PAGE_SIZE{PLATFORM_FRAME_SIZE};
 
   namespace
   {
     // NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
     auto constinit allocator = static_cast<frame_allocator *>(nullptr);
 
+    constexpr auto static unused_page_address = 0x0000'7fff'cafe'faceuz;
+
     auto create_memory_information() -> x86_64::region_allocator::memory_information
     {
       auto const & mbi = boot::bootstrap_information.mbi;
@@ -51,6 +57,67 @@ namespace teachos::memory
       cpu::x86_64::cr0::set(cpu::x86_64::cr0::flags::write_protect);
       cpu::x86_64::i32_efer::set(cpu::x86_64::i32_efer::flags::execute_disable_bit_enable);
     }
+
+    auto inject_faux_pml4(frame_allocator & allocator) -> void
+    {
+      using entry_flags = x86_64::page_table::entry::flags;
+      using page_table = x86_64::page_table;
+
+      auto temporary_page = page::containing(linear_address{unused_page_address});
+      auto temporary_page_address = temporary_page.start_address();
+
+      auto & pml4 = x86_64::paging_root::get();
+
+      // NOLINTBEGIN(cppcoreguidelines-avoid-magic-numbers)
+      auto faux_pml4_frame =
+          allocator.allocate()
+              .and_then([&](auto frame) -> auto {
+                auto index = temporary_page_address >> 39 & 0x1ffu;
+                pml4[index].frame(frame, entry_flags::present | entry_flags::writable);
+                return pml4.next(index);
+              })
+              .and_then([&](auto pml) -> auto {
+                std::construct_at(pml);
+                auto index = temporary_page_address >> 30 & 0x1ffu;
+                (*pml)[index].frame(*allocator.allocate(), entry_flags::present | entry_flags::writable);
+                return pml->next(index);
+              })
+              .and_then([&](auto pml) -> auto {
+                std::construct_at(pml);
+                auto index = temporary_page_address >> 21 & 0x1ffu;
+                (*pml)[index].frame(*allocator.allocate(), entry_flags::present | entry_flags::writable);
+                return pml->next(index);
+              })
+              .transform([&](auto pml) -> auto {
+                std::construct_at(pml);
+                auto index = temporary_page_address >> 12 & 0x1ffu;
+                (*pml)[index].frame(*allocator.allocate(), entry_flags::present | entry_flags::writable);
+                return pml;
+              })
+              .and_then([&](auto pml) -> auto {
+                auto faux_pml4_pointer = std::bit_cast<page_table *>(temporary_page_address.raw());
+                auto faux_pml4 = std::construct_at<page_table>(faux_pml4_pointer);
+
+                auto index = temporary_page_address >> 12 & 0x1ffu;
+                auto frame = (*pml)[index].frame();
+
+                (*faux_pml4)[510].frame(*frame, entry_flags::present | entry_flags::writable);
+                return frame;
+              });
+      // NOLINTEND(cppcoreguidelines-avoid-magic-numbers)
+
+      if (!faux_pml4_frame)
+      {
+        system::panic("[MEM] Failed to map and construct faux PML4");
+      }
+
+      // NOLINTNEXTLINE(cppcoreguidelines-avoid-magic-numbers)
+      pml4[510].frame(*faux_pml4_frame, entry_flags::present | entry_flags::writable);
+      x86_64::tlb_flush_all();
+
+      cio::println("[MEM] Injected faux PML4 as recursive map.");
+    }
+
   }  // namespace
 
   auto active_allocator() -> frame_allocator &
@@ -71,8 +138,9 @@ namespace teachos::memory
       system::panic("[x86_64] Memory management has already been initialized.");
     }
 
-    [[maybe_unused]] auto allocator = create_early_frame_allocator();
+    auto allocator = create_early_frame_allocator();
     enable_cpu_protections();
+    inject_faux_pml4(allocator);
 
     // paging::kernel_mapper kernel(allocator, memory_information);
     // kernel.remap_kernel();