Add a bootstrap physical memory manager.

This will allow the real physical memory manager to use allocations.

zion/CMakeLists.txt

@@ -7,6 +7,7 @@ add_executable(zion
   interrupt/interrupt_enter.s
   memory/kernel_heap.cpp
   memory/paging_util.cpp
+  memory/physical_memory.cpp
   zion.cpp)
 
 target_include_directories(zion

zion/memory/paging_util.cpp

@@ -2,6 +2,7 @@
 
 #include "boot/boot_info.h"
 #include "debug/debug.h"
+#include "memory/physical_memory.h"
 
 #define PRESENT_BIT 0x1
 #define READ_WRITE_BIT 0x2
@@ -39,6 +40,31 @@ uint64_t ShiftForEntryIndexing(uint64_t addr, uint64_t offset) {
   addr <<= 3;
   return addr;
 }
+
+void MapPage(uint64_t virt, uint64_t phys) {
+  if (PageLoaded(virt)) {
+    panic("Allocating Over Existing Page: %m", virt);
+  }
+
+  if (!PageDirectoryPointerLoaded(virt)) {
+    uint64_t page = phys_mem::AllocatePage();
+    *Pml4Entry(virt) = page | PRESENT_BIT | READ_WRITE_BIT;
+    ZeroOutPage(PageDirectoryPointerEntry(virt));
+  }
+  if (!PageDirectoryLoaded(virt)) {
+    uint64_t page = phys_mem::AllocatePage();
+    *PageDirectoryPointerEntry(virt) = page | PRESENT_BIT | READ_WRITE_BIT;
+    ZeroOutPage(PageDirectoryEntry(virt));
+  }
+  if (!PageTableLoaded(virt)) {
+    uint64_t page = phys_mem::AllocatePage();
+    *PageDirectoryEntry(virt) = page | PRESENT_BIT | READ_WRITE_BIT;
+    ZeroOutPage(PageTableEntry(virt));
+  }
+
+  *PageTableEntry(virt) = PageAlign(phys) | PRESENT_BIT | READ_WRITE_BIT;
+  ZeroOutPage(reinterpret_cast<uint64_t*>(virt));
+}
 }  // namespace
 
 void InitPaging() {
@@ -55,10 +81,10 @@ void InitializePml4(uint64_t pml4_physical_addr) {
   pml4_virtual[0x1FE] = recursive_entry;
 }
 
-void AllocatePageDirectoryPointer(uint64_t addr);
-void AllocatePageDirectory(uint64_t addr);
-void AllocatePageTable(uint64_t addr);
-void AllocatePage(uint64_t addr) { panic("Page Allocation Not Implemented."); }
+void AllocatePage(uint64_t addr) {
+  uint64_t physical_page = phys_mem::AllocatePage();
+  MapPage(addr, physical_page);
+}
 
 void EnsureResident(uint64_t addr, uint64_t size) {
   uint64_t max = addr + size;

zion/memory/physical_memory.cpp

@@ -0,0 +1,53 @@
+#include "memory/physical_memory.h"
+
+#include "boot/boot_info.h"
+#include "debug/debug.h"
+
+namespace phys_mem {
+namespace {
+
+struct BootstrapMemory {
+  uint64_t init_page = 0;
+  uint64_t next_page = 0;
+  uint64_t max_page = 0;
+};
+
+static BootstrapMemory gBootstrap;
+static bool gBootstrapEnabled = false;
+
+};  // namespace
+
+void InitBootstrapPageAllocation() {
+  const limine_memmap_response& memmap = boot::GetMemoryMap();
+  for (uint64_t i = 0; i < memmap.entry_count; i++) {
+    const limine_memmap_entry& entry = *memmap.entries[i];
+    // We may want to chose a high address space to not limit
+    // the number of buffers we can allocate later but
+    // if we limit the number of pages this should be fine.
+    // Currently set to the minimum of 3 for one kernel heap allocation:
+    // PageDirectory + PageTable + Page
+    if (entry.type == 0 && entry.length >= 0x3000) {
+      gBootstrap.init_page = entry.base;
+      gBootstrap.next_page = entry.base;
+      gBootstrap.max_page = entry.base + 0x3000;
+      gBootstrapEnabled = true;
+      return;
+    }
+  }
+}
+
+uint64_t AllocatePage() {
+  if (!gBootstrapEnabled) {
+    panic("No Bootstrap Memory Manager");
+  }
+
+  uint64_t page = gBootstrap.next_page;
+  if (page == gBootstrap.max_page) {
+    panic("Bootstrap Memory Manager OOM");
+  }
+  gBootstrap.next_page += 0x1000;
+
+  return page;
+}
+
+}  // namespace phys_mem

zion/memory/physical_memory.h

@@ -0,0 +1,18 @@
+#pragma once
+
+#include <stdint.h>
+
+namespace phys_mem {
+
+// Called before creating a kernel heap object
+// that allows dynamic allocation. The real
+// PhysicalMemoryManager requires some allocations
+// to initialize so we need this first.
+void InitBootstrapPageAllocation();
+
+void InitPhysicalMemoryManager();
+
+uint64_t AllocatePage();
+void FreePage(uint64_t page);
+
+}  // namespace phys_mem

zion/zion.cpp

@@ -1,21 +1,22 @@
 #include <stdint.h>
 
-#include "boot/boot_info.h"
-#include "boot/limine.h"
 #include "common/gdt.h"
 #include "debug/debug.h"
 #include "interrupt/interrupt.h"
 #include "memory/kernel_heap.h"
 #include "memory/paging_util.h"
+#include "memory/physical_memory.h"
 
 extern "C" void zion() {
   InitGdt();
   InitIdt();
   InitPaging();
 
+  phys_mem::InitBootstrapPageAllocation();
   KernelHeap heap(0xFFFFFFFF'40000000, 0xFFFFFFFF'80000000);
   heap.Allocate(1);
 
+  dbgln("Sleeping!");
   while (1)
     ;
 }