From e284d574ed9237a215d994861cc502452fec11ce Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@ost.ch>
Date: Fri, 13 Mar 2026 22:28:50 +0100
Subject: kernel/memory: implement basic bitmap allocator

---
 arch/x86_64/kapi/memory.cpp | 54 ++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 51 insertions(+), 3 deletions(-)

(limited to 'arch/x86_64/kapi/memory.cpp')

diff --git a/arch/x86_64/kapi/memory.cpp b/arch/x86_64/kapi/memory.cpp
index b71fa17..48aab9f 100644
--- a/arch/x86_64/kapi/memory.cpp
+++ b/arch/x86_64/kapi/memory.cpp
@@ -18,14 +18,17 @@
 
 #include <kstd/print>
 
+#include <multiboot2/constants.hpp>
 #include <multiboot2/information.hpp>
 
+#include <algorithm>
 #include <atomic>
 #include <bit>
 #include <cstddef>
 #include <cstdint>
 #include <memory>
 #include <optional>
+#include <ranges>
 #include <span>
 #include <utility>
 
@@ -37,6 +40,10 @@ namespace kapi::memory
     constexpr auto static unused_page_address = linear_address{0x0000'7fff'cafe'faceuz};
     constexpr auto static recursive_page_map_index = arch::memory::page_table::entry_count - 2;
 
+    auto constinit region_based_allocator = std::optional<arch::memory::region_allocator>{};
+    auto constinit allocation_buffer = std::optional<buffered_allocator<4>>{};
+    auto constinit recursive_page_mapper = std::optional<arch::memory::recursive_page_mapper>{};
+
     //! Instantiate a basic, memory region based, early frame allocator for remapping.
     auto collect_memory_information()
     {
@@ -150,9 +157,42 @@ namespace kapi::memory
       }
     }
 
-    auto constinit region_based_allocator = std::optional<arch::memory::region_allocator>{};
-    auto constinit allocation_buffer = std::optional<buffered_allocator<4>>{};
-    auto constinit recursive_page_mapper = std::optional<arch::memory::recursive_page_mapper>{};
+    auto handoff_to_kernel_pmm(frame_allocator & new_allocator) -> void
+    {
+      auto memory_map = boot::bootstrap_information.mbi->memory_map();
+
+      for (auto const & region : memory_map.regions() | std::views::filter([](auto const & region) {
+                                   return region.type == multiboot2::memory_type::available;
+                                 }))
+      {
+        auto start = frame::containing(physical_address{region.base});
+        auto count = region.size_in_B / page::size;
+        new_allocator.release_many({start, count});
+      }
+
+      auto next_free_frame = region_based_allocator->next_free_frame();
+      if (!next_free_frame)
+      {
+        system::panic("[x86_64:MEM] No more free memory!");
+      }
+
+      std::ranges::for_each(std::views::iota(kapi::memory::frame{}, *next_free_frame),
+                            [&](auto frame) { new_allocator.mark_used(frame); });
+
+      auto image_start = frame::containing(physical_address{&arch::boot::_start_physical});
+      auto image_end = frame::containing(physical_address{&arch::boot::_end_physical}) + 1;
+
+      std::ranges::for_each(std::views::iota(image_start, image_end),
+                            [&](auto frame) { new_allocator.mark_used(frame); });
+
+      auto mbi_base = std::bit_cast<std::uintptr_t>(boot::bootstrap_information.mbi);
+      auto mbi_size = boot::bootstrap_information.mbi->size_bytes();
+      auto mbi_address = physical_address{mbi_base & ~std::bit_cast<std::uintptr_t>(&arch::boot::TEACHOS_VMA)};
+      auto mbi_start = frame::containing(mbi_address);
+      auto mbi_end = frame::containing(physical_address{mbi_address.raw() + mbi_size}) + 1;
+
+      std::ranges::for_each(std::views::iota(mbi_start, mbi_end), [&](auto frame) { new_allocator.mark_used(frame); });
+    }
 
   }  // namespace
 
@@ -189,6 +229,14 @@ namespace kapi::memory
 
     set_frame_allocator(*allocation_buffer);
     set_page_mapper(*recursive_page_mapper);
+
+    auto memory_map = boot::bootstrap_information.mbi->memory_map();
+    auto highest_byte = std::ranges::max(std::views::transform(
+        std::views::filter(memory_map.regions(),
+                           [](auto const & region) { return region.type == multiboot2::memory_type::available; }),
+        [](auto const & region) { return region.base + region.size_in_B; }));
+
+    init_pmm(frame::containing(physical_address{highest_byte}).number() + 1, handoff_to_kernel_pmm);
   }
 
 }  // namespace kapi::memory
-- 
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