X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=src%2Fuserprog%2Fpagedir.c;h=f26496d79467aa316e5b0f13953c2c07eb6d4fa4;hb=8382bdd7884a6d38f7529e0517dd9a7083f4ce73;hp=39a8f0a3af286f9227cf7d7226f19b7cd18e50e4;hpb=e6a09e68f6d8b9c63adf8206777495dc3cd2a8b1;p=pintos-anon

diff --git a/src/userprog/pagedir.c b/src/userprog/pagedir.c
index 39a8f0a..f26496d 100644
--- a/src/userprog/pagedir.c
+++ b/src/userprog/pagedir.c
@@ -6,19 +6,29 @@
 #include "threads/mmu.h"
 #include "threads/palloc.h"
 
+/* Creates a new page directory that has mappings for kernel
+   virtual addresses, but none for user virtual addresses.
+   Returns the new page directory, or a null pointer if memory
+   allocation fails. */
 uint32_t *
 pagedir_create (void) 
 {
-  uint32_t *pd = palloc_get (0);
+  uint32_t *pd = palloc_get_page (0);
   memcpy (pd, base_page_dir, PGSIZE);
   return pd;
 }
 
+/* Destroys page directory PD, freeing all the pages it
+   references. */
 void
 pagedir_destroy (uint32_t *pd) 
 {
   uint32_t *pde;
 
+  if (pd == NULL)
+    return;
+
+  ASSERT (pd != base_page_dir);
   for (pde = pd; pde < pd + pd_no (PHYS_BASE); pde++)
     if (*pde & PG_P) 
       {
@@ -27,30 +37,38 @@ pagedir_destroy (uint32_t *pd)
         
         for (pte = pt; pte < pt + PGSIZE / sizeof *pte; pte++)
           if (*pte & PG_P) 
-            palloc_free (pte_get_page (*pte));
-        palloc_free (pt);
+            palloc_free_page (pte_get_page (*pte));
+        palloc_free_page (pt);
       }
-  palloc_free (pd);
+  palloc_free_page (pd);
 }
 
+/* Returns the mapping of user virtual address UADDR in page
+   directory PD into a kernel virtual address.
+   If UADDR is unmapped, behavior varies based on CREATE:
+   if CREATE is true, then a new, zeroed page is created and a
+   pointer into it is returned,
+   otherwise a null pointer is returned.
+   Also returns a null pointer if UADDR is a kernel address. */
 static uint32_t *
-lookup_page (uint32_t *pd, void *upage, bool create)
+lookup_page (uint32_t *pd, void *uaddr, bool create)
 {
-  uint32_t *pt;
-  uint32_t *pde;
+  uint32_t *pt, *pde;
 
   ASSERT (pd != NULL);
-  ASSERT (pg_ofs (upage) == 0);
-  ASSERT (upage < PHYS_BASE);
 
-  /* Check for a page table for UPAGE.
+  /* Make sure it's a user address. */
+  if (uaddr >= PHYS_BASE)
+    return NULL;
+
+  /* Check for a page table for UADDR.
      If one is missing, create one if requested. */
-  pde = pd + pd_no (upage);
+  pde = pd + pd_no (uaddr);
   if (*pde == 0) 
     {
       if (create)
         {
-          pt = palloc_get (PAL_ZERO);
+          pt = palloc_get_page (PAL_ZERO);
           if (pt == NULL) 
             return NULL; 
       
@@ -62,16 +80,26 @@ lookup_page (uint32_t *pd, void *upage, bool create)
 
   /* Return the page table entry. */
   pt = pde_get_pt (*pde);
-  return &pt[pt_no (upage)];
+  return &pt[pt_no (uaddr)];
 }
 
+/* Adds a mapping from user virtual address UPAGE to kernel
+   virtual address KPAGE in page directory PD.
+   UPAGE must not already be mapped.
+   If WRITABLE is true, the new page is read/write;
+   otherwise it is read-only.
+   Returns true if successful, false if memory allocation
+   failed. */
 bool
 pagedir_set_page (uint32_t *pd, void *upage, void *kpage,
                   bool writable) 
 {
   uint32_t *pte;
 
+  ASSERT (pg_ofs (upage) == 0);
   ASSERT (pg_ofs (kpage) == 0);
+  ASSERT (upage < PHYS_BASE);
+  ASSERT (pagedir_get_page (pd, upage) == NULL);
 
   pte = lookup_page (pd, upage, true);
   if (pte != NULL) 
@@ -83,21 +111,18 @@ pagedir_set_page (uint32_t *pd, void *upage, void *kpage,
     return false;
 }
 
+/* Returns the kernel virtual address that user virtual address
+   UADDR is mapped to in PD, or a null pointer if there is no
+   mapping. */
 void *
-pagedir_get_page (uint32_t *pd, void *upage) 
+pagedir_get_page (uint32_t *pd, const void *uaddr) 
 {
-  uint32_t *pte = lookup_page (pd, upage, false);
+  uint32_t *pte = lookup_page (pd, (void *) uaddr, false);
   return pte != NULL && *pte != 0 ? pte_get_page (*pte) : NULL;
 }
 
-void
-pagedir_clear_page (uint32_t *pd, void *upage)
-{
-  uint32_t *pte = lookup_page (pd, upage, false);
-  if (pte != NULL)
-    *pte = 0;
-}
-
+/* Loads page directory PD into the CPU's page directory base
+   register. */
 void
 pagedir_activate (uint32_t *pd) 
 {