virtual_mm: Implement physical to virtual mapping

2 files changed, 37 insertions, 8 deletions

diff --git a/kernel/include/mm/virtual_mm.h b/kernel/include/mm/virtual_mm.h
index 52eb92c..980e809 100644
--- a/kernel/include/mm/virtual_mm.h
+++ b/kernel/include/mm/virtual_mm.h
@@ -25,9 +25,6 @@
 #define PAGE_DIRECTORY_SIZE 1024
 #define PAGE_TABLE_SIZE 1024
 
-#define PAGE_DIRECTORY_INDEX(virtual_address) ((virtual_address >> 22) & 0x3ff)
-#define PAGE_TABLE_INDEX(virtual_address) ((virtual_address >> 12) & 0x3ff)
-
 #define PDE_PRESENT(x) x
 #define PDE_WRITABLE(x) ((x) << 1)
 #define PDE_USER(x) ((x) << 2)
@@ -42,7 +39,9 @@
 /* Page table address */
 #define PDE_FRAME(x) ((x) &0xFFFFF000)
 
-#define GET_PDE_FRAME(x) ((*x) >> 12)
+#define PDE_IS_PRESENT(pd_entry) ((*pd_entry) & 1)
+#define GET_PDE_FRAME(virtual_address) (((uint32_t) virtual_address) >> 22)
+#define PDE_GET_TABLE(pd_entry) ((*pd_entry) & ~0xfff)
 
 #define PTE_PRESENT(x) x
 #define PTE_WRITABLE(x) ((x) << 1)
@@ -58,8 +57,9 @@
 /* Left shift by 12 because we only need the bits from the twelfth bit. */
 #define PTE_FRAME(x) ((x) << 12)
 
-#define PTE_IS_PRESENT(x) ((x) &1)
-#define GET_PTE_FRAME(x) ((*x) >> 12)
+#define PTE_IS_PRESENT(pt_entry) ((*pt_entry) & 1)
+#define GET_PTE_FRAME(virtual_address)                                        \
+  ((((uint32_t) virtual_address) >> 12) & 0x3ff)
 
 #define ADD_ATTRIB(entry, attribute) (*entry |= (attribute))
 
@@ -78,4 +78,9 @@ bool virtual_mm_switch_page_directory(uint32_t *page_directory);
  */
 void virtual_mm_initialize(void);
 
+/*
+ * Map a physical address to a virtual address
+ */
+void virtual_mm_map_page(void *physical_address, void *virtual_address);
+
 #endif
diff --git a/kernel/mm/virtual_mm/virtual_mm.c b/kernel/mm/virtual_mm/virtual_mm.c
index 9c8292e..c69d194 100644
--- a/kernel/mm/virtual_mm/virtual_mm.c
+++ b/kernel/mm/virtual_mm/virtual_mm.c
@@ -62,10 +62,9 @@ virtual_mm_initialize(void)
   uint32_t *table = physical_mm_allocate_block();
   if (!table)
     ASSERT_NOT_REACHED();
-  printk("debug", "Page table is at: 0x%x", table);
 
   for (uint32_t i = 0; i < 1024; i++)
-    table[i] = 0x2;
+    table[i] = 0;
 
   /* Identity map the first 4MiB, excluding the 4th MiB
    * (maps 4KiB 1024 times) */
@@ -86,3 +85,28 @@ virtual_mm_initialize(void)
   virtual_mm_switch_page_directory(page_directory);
   virtual_mm_enable_paging();
 }
+
+void
+virtual_mm_map_page(void *physical_address, void *virtual_address)
+{
+  uint32_t *pd_entry = &current_page_directory[GET_PDE_FRAME(virtual_address)];
+
+  uint32_t *table = 0;
+  /* If the pd_entry isn't present, allocate a block for it, zero the table,
+   * and set the pd_entry's frame to the table's address. */
+  if (!PDE_IS_PRESENT(pd_entry)) {
+    table = physical_mm_allocate_block();
+    if (!table)
+      ASSERT_NOT_REACHED();
+
+    for (uint32_t i = 0; i < 1024; i++)
+      table[i] = 0;
+
+    *pd_entry = PDE_FRAME((uint32_t) table) | PDE_PRESENT(1) | PDE_WRITABLE(1);
+  } else
+    table = (uint32_t *) PDE_GET_TABLE(pd_entry);
+
+  uint32_t *pt_entry = &table[GET_PTE_FRAME(virtual_address)];
+  *pt_entry = PTE_FRAME((uint32_t) physical_address) | PTE_PRESENT(1)
+              | PTE_WRITABLE(1);
+}