Rewrite resource subsystem

kernel/amd64/mm.c

@@ -43,6 +43,8 @@ void amd64_load_kernel_cr3 (void) {
   }
 }
 
+struct pd* mm_get_kernel_pd (void) { return &kernel_pd; }
+
 /* Extract PML info from virtual address */
 static struct pg_index amd64_mm_page_index (uint64_t vaddr) {
   struct pg_index ret;