From fdcdb9acab60460000875d561d130ee37c9f8fca Mon Sep 17 00:00:00 2001
From: ngiddings <nathang567@gmail.com>
Date: Sat, 17 Apr 2021 00:52:16 -0500
Subject: [PATCH] Updated virtual memory manager Added page flags Added
 function current_address_space() Fixed create_address_space() Renamed some
 fields in page_table_entry_t to fit naming scheme

---
 include/mmgr.h | 20 +++++++++++++++++++-
 src/x86/mmgr.c | 40 ++++++++++++++++++----------------------
 2 files changed, 37 insertions(+), 23 deletions(-)

diff --git a/include/mmgr.h b/include/mmgr.h
index dc80161..12e86c8 100644
--- a/include/mmgr.h
+++ b/include/mmgr.h
@@ -3,6 +3,15 @@
 #include "pageallocator.h"
 #include "types/physaddr.h"
 
+enum page_flag_t
+{
+    PAGE_RW = 1,
+    PAGE_EXECUTABLE = 1 << 1,
+    PAGE_USERMODE = 1 << 2
+};
+
+extern const size_t page_size;
+
 /**
  * @brief Create a new top-level page table and map the kernel in it.
  * 
@@ -19,6 +28,15 @@ physaddr_t create_address_space(struct page_stack_t *page_stack);
  */
 void load_address_space(physaddr_t table);
 
+/**
+ * @brief Returns the physical address of the top-level page table currently in
+ * use.
+ * 
+ * @param table 
+ * @return physaddr_t 
+ */
+physaddr_t current_address_space();
+
 /**
  * @brief Maps a single page with the specified flags.
  * 
@@ -36,4 +54,4 @@ int map_page(struct page_stack_t *page_stack, void *page, physaddr_t frame, int
  * @param page 
  * @return physaddr_t 
  */
-physaddr_t unmap_page(void *page);
\ No newline at end of file
+physaddr_t unmap_page(void *page);
diff --git a/src/x86/mmgr.c b/src/x86/mmgr.c
index a12be9f..c4edb6a 100644
--- a/src/x86/mmgr.c
+++ b/src/x86/mmgr.c
@@ -11,28 +11,17 @@ const size_t page_bits = 12;
 struct page_table_entry_t
 {
     uint32_t present : 1;
-
     uint32_t rw : 1;
-
     uint32_t usermode : 1;
-
-    uint32_t writeThrough : 1;
-
-    uint32_t cacheDisable : 1;
-
+    uint32_t write_through : 1;
+    uint32_t cache_disable : 1;
     uint32_t accessed : 1;
-
     uint32_t dirty : 1;
-
     uint32_t pat : 1;
-
     uint32_t global : 1;
-
     uint32_t shared : 1;
-
     uint32_t ignored : 2;
-
-    uint32_t physicalAddress : 20;
+    uint32_t physical_address : 20;
 };
 
 struct page_table_entry_t *page_tables = (struct page_table_entry_t *)0xFFC00000;
@@ -47,12 +36,14 @@ physaddr_t create_address_space(struct page_stack_t *page_stack)
         return S_OUT_OF_MEMORY;
     }
     struct page_table_entry_t buffer = page_directory[0];
-    page_directory[0].physicalAddress = table >> page_bits;
+    page_directory[0].physical_address = table >> page_bits;
     asm volatile("invlpg 0xFFC00000" ::
                      : "memory");
     memset((void *)page_tables, 0, 1022 * 4);
     page_tables[1022] = page_directory[1022];
-    page_tables[1023] = page_directory[1023];
+    page_tables[1023].physical_address = table >> page_bits;
+    page_tables[1023].present = 1;
+    page_tables[1023].rw = 1;
     page_directory[0] = buffer;
     asm volatile("invlpg 0xFFC00000" ::
                      : "memory");
@@ -67,6 +58,11 @@ void load_address_space(physaddr_t table)
                  : "memory");
 }
 
+physaddr_t current_address_space()
+{
+    return page_directory[1023].physical_address << 12;
+}
+
 int map_page(struct page_stack_t *page_stack, void *page, physaddr_t frame, int flags)
 {
     if ((size_t)page % page_size != 0 || frame % page_size != 0)
@@ -82,15 +78,15 @@ int map_page(struct page_stack_t *page_stack, void *page, physaddr_t frame, int
         {
             return S_OUT_OF_MEMORY;
         }
-        page_directory[directory_index].physicalAddress = new_table >> page_bits;
+        page_directory[directory_index].physical_address = new_table >> page_bits;
         page_directory[directory_index].present = 1;
-        page_directory[directory_index].usermode = 0;
+        page_directory[directory_index].usermode = (directory_index < 1022) ? 1 : 0;
         page_directory[directory_index].rw = 1;
     }
-    page_tables[table_index].physicalAddress = frame >> 12;
+    page_tables[table_index].physical_address = frame >> 12;
     page_tables[table_index].present = 1;
-    page_tables[table_index].usermode = 1;
-    page_tables[table_index].rw = 1;
+    page_tables[table_index].usermode = (flags & PAGE_USERMODE) ? 1 : 0;
+    page_tables[table_index].rw = (flags & PAGE_RW) ? 1 : 0;
     asm volatile("invlpg (%0)"
                  :
                  : "r"(page)
@@ -112,7 +108,7 @@ physaddr_t unmap_page(void *page)
     }
     else
     {
-        physaddr_t frame = page_tables[table_index].physicalAddress << page_bits;
+        physaddr_t frame = page_tables[table_index].physical_address << page_bits;
         memset(&page_tables[table_index], 0, sizeof(struct page_table_entry_t));
         asm volatile("invlpg (%0)"
                      :