only identity map the start of the kernel

src/arch/x86_64/boot/boot.asm

@@ -1,6 +1,7 @@
 global _start
 global pml4
 extern x86_64_main
+extern kernel_end
 
 %define FLAGS       0b10
 %define MAGIC       0x1BADB002
@@ -43,6 +44,8 @@ section .data
         dd 0
     multiboot_magic:
         dd 0
+    kernel_page_count:
+        dd 0
 
 section .text
     bits 32
@@ -98,10 +101,18 @@ section .text
         mov eax, pd
         or eax, 0x03
         mov [pdpt], eax
-        ; Map first 32 2mb pages for the kernel for a total of 64mb
+
+        ; Calculate how many 2mb pages we need to identity map
+        mov ecx, kernel_end
+        add ecx, 0x1FFFFF               ; Page align end of kernel
+        shr ecx, 21                     ; ecx now holds the required pages
+
+        ; Save the page count so we can pass it to c later
+        mov [kernel_page_count], ecx
+
+        ; Identity map the 0x0 to kernel_end
         mov edi, pd
         mov eax, 0x83
-        mov ecx, 32
     .setup_pd:
         mov [edi], eax
         add eax, 0x200000
@@ -150,6 +161,7 @@ section .text
         ; Finally, we call in to c
         mov edi, [multiboot_magic]
         mov esi, [multiboot_info]
+        mov edx, [kernel_page_count]
         call x86_64_main
     .hang:
         hlt

src/arch/x86_64/main.c

@@ -7,7 +7,7 @@
 #include "panic.h"
 #include "util.h"
 
-void x86_64_main(u32 magic, multiboot_info_t* info)
+void x86_64_main(u32 magic, multiboot_info_t* info, u32 kernel_page_count)
 {
     console_clear();
 
@@ -24,8 +24,8 @@ void x86_64_main(u32 magic, multiboot_info_t* info)
     idt_init();
     remap_pic();
 
-    pmm_init(info);
-    vmm_init();
+    pmm_init(kernel_page_count, info);
+    vmm_init(kernel_page_count);
 
     kernel_main();
 }

src/arch/x86_64/mem/pmm.c

@@ -23,7 +23,7 @@ static size_t num_regions = 0;
 
 static u8 page_bitmap[BITMAP_SIZE];
 
-void pmm_init(multiboot_info_t* info)
+void pmm_init(u32 kernel_page_count, multiboot_info_t* info)
 {
     if (!(info->flags & (1 << 6)))
     {
@@ -67,7 +67,7 @@ void pmm_init(multiboot_info_t* info)
 
         for (u64 page = start_page; page < start_page + num_pages; page++)
         {
-            if (page < BITMAP_SIZE * 8)
+            if (page < BITMAP_PAGE_COUNT)
             {
                 page_bitmap[page / 8] &= ~(1 << (page % 8));
             }
@@ -79,21 +79,15 @@ void pmm_init(multiboot_info_t* info)
         }
     }
 
-    // Mark first 32 pages (64mb) as unusable since it is reserved by the bootloader
-    // todo(nub31): This should be revisited. Maybe do a higher half kernel?
-    for (u64 page = 0; page < 32; page++)
+    // The kernel was identity mapped by the kernel, so those bits should be marked as unavailable
+    for (u64 page = 0; page < kernel_page_count; page++)
     {
-        if (page < BITMAP_PAGE_COUNT)
+        if (page >= BITMAP_PAGE_COUNT)
         {
-            if (!(page_bitmap[page / 8] & (1 << (page % 8))))
-            {
-                page_bitmap[page / 8] |= (1 << (page % 8));
-            }
-        }
-        else
-        {
-            panic("Bitmap is not large enough to hold the bootloader reserved memory");
+            panic("Bitmap is not large enough to hold the memory reserved by the kernel");
         }
+
+        page_bitmap[page / 8] |= (1 << (page % 8));
     }
 }
 

src/arch/x86_64/mem/pmm.h

@@ -10,7 +10,7 @@
 // The value must be a multible of 8
 #define MAX_MEMORY GiB(64)
 
-void pmm_init(multiboot_info_t* info);
+void pmm_init(u32 kernel_page_count, multiboot_info_t* info);
 
 // Low level function to allocate a 2mb physical page and return the physical address
 // A return value 0 indicates out of memory

src/arch/x86_64/mem/vmm.c

@@ -20,23 +20,18 @@ static u8 page_bitmap[BITMAP_SIZE];
 
 extern u64 pml4[];
 
-void vmm_init()
+void vmm_init(u32 kernel_page_count)
 {
-    // Mark first 32 pages (64mb) as unusable since it is reserved by the bootloader
-    // todo(nub31): This should be revisited. Maybe do a higher half kernel?
-    for (u64 page = 0; page < 32; page++)
+    // The kernel was identity mapped when we entered long mode,
+    // so those virtual addresses should be marked as unavailable
+    for (u64 page = 0; page < kernel_page_count; page++)
     {
-        if (page < BITMAP_PAGE_COUNT)
+        if (page >= BITMAP_PAGE_COUNT)
         {
-            if (!(page_bitmap[page / 8] & (1 << (page % 8))))
-            {
-                page_bitmap[page / 8] |= (1 << (page % 8));
-            }
-        }
-        else
-        {
-            panic("Bitmap is not large enough to hold the bootloader reserved address space");
+            panic("Bitmap is not large enough to hold the addresses reserved by the kernel");
         }
+
+        page_bitmap[page / 8] |= (1 << (page % 8));
     }
 }
 

src/arch/x86_64/mem/vmm.h

@@ -6,7 +6,7 @@
 // The value must be a multible of 8
 #define ADDRES_SPACE_SIZE GiB(64)
 
-void vmm_init();
+void vmm_init(u32 kernel_page_count);
 
 // Allocates a free page aligned block of virtual addresses
 // A return value 0 indicates that there were not blocks