fixing up paging issues

kernel/memory/mm.c

@@ -13,8 +13,6 @@ static uint32_t max_address = 0;
 static uint32_t total_available_memory = 0;
 static uint8_t memory_bitmap[BITMAP_SIZE];
 
-uint32_t* page_directory;
-
 static void mark_free(uint32_t addr) {
     uint32_t page_index = addr / PAGE_SIZE;
     uint32_t byte_index = page_index / 8;
@@ -56,8 +54,10 @@ static void parse_multiboot_mmap(void* base, uint32_t limit) {
                 continue;
             }
 
+            uint32_t kernel_phys_start = (uint32_t)&__kernel_start - 0xC0000000;
+            uint32_t kernel_phys_end   = (uint32_t)&__kernel_end - 0xC0000000;
             for (uint32_t addr = usable_start; addr < usable_end; addr += 4096) {
-                if (addr <= (uint32_t)&__kernel_end && addr >= (uint32_t)&__kernel_start) {
+                if (addr <= (uint32_t)&kernel_phys_end && addr >= (uint32_t)&kernel_phys_start) {
                     continue;
                 }
 
@@ -78,7 +78,7 @@ static void parse_multiboot_mmap(void* base, uint32_t limit) {
     }
 }
 
-void init_mm(void* mmap_base, uint32_t mmap_limit) {
+void init_pmm(void* mmap_base, uint32_t mmap_limit) {
     for (int i = 0; i < BITMAP_SIZE; i++) {
         memory_bitmap[i] = 0xFF;
     }
@@ -92,7 +92,8 @@ uint32_t total_free_memory() {
     return total_available_memory;
 }
 
-void* alloc_page() {
+// this returns the virtual address of the physical page allocated
+void* alloc_phys_page() {
     for (uint32_t i = 0; i < BITMAP_SIZE; i++) {
         uint8_t b = memory_bitmap[i];
         if (b == 0xFF) {
@@ -103,7 +104,7 @@ void* alloc_page() {
             if ((b & (1 << bit)) == 0) {
                 uint32_t page_addr = (i * 8 + bit) * PAGE_SIZE;
                 mark_used(page_addr);
-                return (void*)page_addr;
+                return (void*)(page_addr + 0xC0000000);
             }
         }
     }
@@ -111,22 +112,19 @@ void* alloc_page() {
     return 0;
 }
 
-void free_page(void* addr) {
+void free_phys_page(void* addr) {
     mark_free((uint32_t)addr);
 }
 
-void init_paging() {
-    page_directory = alloc_page();
+extern uint32_t page_directory[1024];
+extern void flush_tlb();
+extern void disable_pae();
+void init_page_tables() {
+    uint32_t* kernel_table = alloc_phys_page();
     for (int i = 0; i < 1024; i++) {
-        page_directory[i] = 0x0; 
+        kernel_table[i] = (i * PAGE_SIZE) | 0x3;
     }
-
-    uint32_t* page_table = alloc_page();
-    page_directory[0] = (uint32_t)(page_table) | 0x3;
-    for (int i = 0; i < 1024; i++) {
-        page_table[i] = (i * PAGE_SIZE) | 0x3;
-    }
-
-    extern void load_page_directory(uint32_t* pd);
-    load_page_directory(page_directory);
+    uint32_t* phys_table = kernel_table - 0xC000000;
+    page_directory[768] = (uint32_t)(phys_table) | 0x3;
+    flush_tlb();
 }

kernel/memory/mm.h

@@ -7,13 +7,12 @@ typedef struct __attribute__((packed)) {
     uint32_t addr;
 } mem_page_t;
 
-void init_mm(void* mmap_base, uint32_t mmap_limit);
+void init_pmm(void* mmap_base, uint32_t mmap_limit);
 uint32_t total_free_memory();
 
 void* alloc_page();
 void free_page(void* addr);
 
-void init_paging();
-void enable_paging();
+void init_page_tables();
 
 #endif 

kernel/memory/mm_stubs.S

@@ -1,21 +1,11 @@
-.code32 
-.global load_page_directory
-load_page_directory: 
-    push %ebp 
-    mov %esp, %ebp 
-    
-    mov 8(%ebp), %eax
+.code32
+.global flush_tlb
+flush_tlb:
+    mov %cr3, %eax
     mov %eax, %cr3
-
-    leave 
     ret
-
-.global enable_paging
-enable_paging:
-    mov %eax, %cr0
-    orl $0x80000000, %eax
-    mov %cr0, %eax
-    jmp 1f
-1:
+     
+.global disable_pae
+disable_pae: 
     ret
-     
+