From 40804526a58ddf2cc0df0750550c8dcfa7b7c57c Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@ost.ch>
Date: Mon, 15 Dec 2025 11:34:30 +0100
Subject: x86_64/boot: use high-mem address of MBI

---
 arch/x86_64/include/x86_64/boot/boot.hpp         | 3 +++
 arch/x86_64/src/boot/entry64.s                   | 1 +
 arch/x86_64/src/kapi/memory.cpp                  | 6 ++----
 arch/x86_64/src/memory/recursive_page_mapper.cpp | 3 +--
 4 files changed, 7 insertions(+), 6 deletions(-)

(limited to 'arch')

diff --git a/arch/x86_64/include/x86_64/boot/boot.hpp b/arch/x86_64/include/x86_64/boot/boot.hpp
index 6dcd2de..2c44659 100644
--- a/arch/x86_64/include/x86_64/boot/boot.hpp
+++ b/arch/x86_64/include/x86_64/boot/boot.hpp
@@ -56,7 +56,10 @@ namespace teachos::boot
 
   struct information
   {
+    //! A pointer to the loader provided Multiboot2 Information structure.
     multiboot2::information_view const * mbi;
+
+    //! The index of the next character to be written in the VGA text buffer after handoff.
     std::size_t vga_buffer_index;
   };
 
diff --git a/arch/x86_64/src/boot/entry64.s b/arch/x86_64/src/boot/entry64.s
index 2932354..657b0a8 100644
--- a/arch/x86_64/src/boot/entry64.s
+++ b/arch/x86_64/src/boot/entry64.s
@@ -33,6 +33,7 @@ _entry64:
     mov %rsp, %rbp
 
     mov multiboot_information_pointer, %rax
+    or $TEACHOS_VMA, %rax
     mov vga_buffer_pointer, %rdx
     sub $0xb8000, %rdx
     mov %rax, (bootstrap_information)
diff --git a/arch/x86_64/src/kapi/memory.cpp b/arch/x86_64/src/kapi/memory.cpp
index ae0401e..748893a 100644
--- a/arch/x86_64/src/kapi/memory.cpp
+++ b/arch/x86_64/src/kapi/memory.cpp
@@ -138,8 +138,8 @@ namespace teachos::memory
     {
       auto mbi_base = std::bit_cast<std::uintptr_t>(boot::bootstrap_information.mbi);
       auto mbi_size = boot::bootstrap_information.mbi->size_bytes();
-      auto mbi_physical_start = physical_address{mbi_base};
-      auto mbi_virtual_start = linear_address{mbi_base + std::bit_cast<std::uintptr_t>(&boot::x86_64::TEACHOS_VMA)};
+      auto mbi_physical_start = physical_address{mbi_base & ~std::bit_cast<std::uintptr_t>(&boot::x86_64::TEACHOS_VMA)};
+      auto mbi_virtual_start = linear_address{mbi_base};
       auto mbi_block_count = (mbi_size + PLATFORM_FRAME_SIZE - 1) / PLATFORM_FRAME_SIZE;
 
       for (auto i = 0uz; i < mbi_block_count; ++i)
@@ -148,8 +148,6 @@ namespace teachos::memory
         auto frame = frame::containing(mbi_physical_start) + 1;
         mapper.map(page, frame, page_mapper::flags::empty);
       }
-
-      boot::bootstrap_information.mbi = std::bit_cast<multiboot2::information_view const *>(mbi_virtual_start.raw());
     }
 
   }  // namespace
diff --git a/arch/x86_64/src/memory/recursive_page_mapper.cpp b/arch/x86_64/src/memory/recursive_page_mapper.cpp
index 798233a..ef234ad 100644
--- a/arch/x86_64/src/memory/recursive_page_mapper.cpp
+++ b/arch/x86_64/src/memory/recursive_page_mapper.cpp
@@ -14,8 +14,7 @@ namespace teachos::memory::x86_64
     //! On any level above PML1, the entries need to not be no_execute, because the image is densely packed. The entries
     //! also need to be writable, since the mapping is being performed through the recursive page map hierarchy. When
     //! setting the final entry in the PML1, the actually desired flags are set as is, with the present bit
-    //! added, thus
-    //! still enforcing non-writability and non-execution of the affected page.
+    //! added, thus still enforcing non-writability and non-execution of the affected page.
     template<std::size_t Level>
       requires(Level > 1uz && Level <= PLATFORM_PAGING_LEVELS)
     auto do_map(recursive_page_table<Level> * pml, page page, frame_allocator & allocator, page_mapper::flags flags)
-- 
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