fix (kernel): polished up page map management

kernel/inc/mm/page_map.h

@@ -17,7 +17,6 @@
 #define NOX_PAGE_MAP_H
 
 #include "utils/stdtypes.h"
-#include "boot/boot_info.h"
 
 #define VIRTUAL_ADDRESS_MAX 0x1000000000000     // 256 TB (the limit of PML4s)
 
@@ -28,6 +27,7 @@ typedef enum {
     PM_FLAG_WRITE_THROUGH   = 0b0000000000001000,   // 1 << 3
     PM_FLAG_CACHE_DISABLED  = 0b0000000000010000,   // 1 << 4
     PM_FLAG_ACCESSED        = 0b0000000000100000,   // 1 << 5
+    PM_FLAG_DIRTY           = 0b0000000001000000,   // 1 << 6
     PM_FLAG_LARGER_PAGES    = 0b0000000010000000,   // 1 << 7
     PM_FLAG_CUSTOM_0        = 0b0000001000000000,   // 1 << 9
     PM_FLAG_CUSTOM_1        = 0b0000010000000000,   // 1 << 10
@@ -51,7 +51,7 @@ bool                page_map_entry_get_flag         (uint64_t* entry, page_map_f
 void                page_map_entry_set_address      (uint64_t* entry, void* address);
 void*               page_map_entry_get_address      (uint64_t* entry);
 
-void                paging_init                     (boot_info_T* boot_info);
+void                paging_init                     ();
 
 extern page_map_T* g_kernel_page_map;
 

kernel/src/kmain.c

@@ -31,7 +31,7 @@ void kernel_init(boot_info_T* boot_info) {
     gdt_init();
     pframe_manager_init(boot_info);
     idt_init();
-    paging_init(boot_info);
+    paging_init();
 }
 
 void kmain(boot_info_T boot_info) {

kernel/src/mm/page_map.c

@@ -63,11 +63,63 @@ void page_map_map_memory(page_map_T* page_map, void* virtual_address, void* phys
 }
 
 void page_map_unmap_memory(page_map_T* page_map, void* virtual_address) {
+    virtual_address = (void*)FLOOR_TO((uint64_t)virtual_address, PFRAME_SIZE);
 
+    // Intel's Developer Manual has a nice graph, that explains how these indexes are calculated
+    uint16_t page_index                 =  ((uint64_t)virtual_address >> 12) & 0x1FF;
+    uint16_t page_table_index           =  ((uint64_t)virtual_address >> 21) & 0x1FF;
+    uint16_t page_directory_index       =  ((uint64_t)virtual_address >> 30) & 0x1FF;
+    uint16_t page_directory_page_index  =  ((uint64_t)virtual_address >> 39) & 0x1FF;
+
+    if (!page_map_entry_get_flag(&page_map->entries[page_directory_page_index], PM_FLAG_PRESENT)) {
+        return;
+    }
+    page_map_T* page_directory_page = page_map_entry_get_address(&page_map->entries[page_directory_page_index]);
+
+    if (!page_map_entry_get_flag(&page_directory_page->entries[page_directory_index], PM_FLAG_PRESENT)) {
+        return;
+    }
+    page_map_T* page_directory = page_map_entry_get_address(&page_directory_page->entries[page_directory_index]);
+
+    if (!page_map_entry_get_flag(&page_directory->entries[page_table_index], PM_FLAG_PRESENT)) {
+        return;
+    }
+    page_map_T* page_table = page_map_entry_get_address(&page_directory->entries[page_table_index]);
+
+    // zeroing out the complete entry
+    page_table->entries[page_index] = 0;
 }
 
 void page_map_destruct(page_map_T* page_map) {
+    for (uint16_t page_directory_page_index = 0; page_directory_page_index < 512; page_directory_page_index++) {
+        if (!page_map_entry_get_flag(&page_map->entries[page_directory_page_index], PM_FLAG_PRESENT)) {
+            continue;
+        }
+        page_map_T* page_directory_page = page_map_entry_get_address(&page_map->entries[page_directory_page_index]);
 
+        for (uint16_t page_directory_index = 0; page_directory_index < 512; page_directory_index++) {
+            if (!page_map_entry_get_flag(&page_directory_page->entries[page_directory_index], PM_FLAG_PRESENT)) {
+                continue;
+            }
+            page_map_T *page_directory = page_map_entry_get_address(&page_directory_page->entries[page_directory_index]);
+
+            for (uint16_t page_table_index = 0; page_table_index < 512; page_table_index++) {
+                if (!page_map_entry_get_flag(&page_directory->entries[page_table_index], PM_FLAG_PRESENT)) {
+                    continue;
+                }
+                page_map_T *page_table = page_map_entry_get_address(&page_directory->entries[page_table_index]);
+
+
+                pframe_free(page_table);
+            }
+
+            pframe_free(page_directory);
+        }
+
+        pframe_free(page_directory_page);
+    }
+
+    pframe_free(page_map);
 }
 
 void page_map_entry_set_flags(uint64_t* entry, uint64_t flags) {
@@ -89,7 +141,7 @@ void* page_map_entry_get_address(uint64_t* entry) {
     return (void*)(*entry & 0x000ffffffffff000);
 }
 
-void paging_init(boot_info_T* boot_info) {
+void paging_init() {
     // fetching the page map that was created by the bootloader
     g_kernel_page_map = page_map_fetch_current();