X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=src%2Fuserprog%2Fpagedir.c;h=d9cfd301e5d5997887eb64e894f8c82e5f282a03;hb=e49b5cba9beb8ffe4a9fd1daf36a23525a32fa5d;hp=937f433da030505e701d00f7a9bb8a15feb49dcb;hpb=20b178aeeb0e0badfd1676c7cb0db6f46bf00a39;p=pintos-anon

diff --git a/src/userprog/pagedir.c b/src/userprog/pagedir.c
index 937f433..d9cfd30 100644
--- a/src/userprog/pagedir.c
+++ b/src/userprog/pagedir.c
@@ -187,15 +187,23 @@ pagedir_activate (uint32_t *pd)
 {
   if (pd == NULL)
     pd = base_page_dir;
-  asm volatile ("movl %0,%%cr3" :: "r" (vtop (pd)));
+
+  /* Store the physical address of the page directory into CR3
+     aka PDBR (page directory base register).  This activates our
+     new page tables immediately.  See [IA32-v2a] "MOV--Move
+     to/from Control Registers" and [IA32-v3] 3.7.5. */
+  asm volatile ("mov %%cr3, %0" :: "r" (vtop (pd)));
 }
 
 /* Returns the currently active page directory. */
 static uint32_t *
 active_pd (void) 
 {
-  uint32_t *pd;
-
-  asm ("movl %%cr3,%0" : "=r" (pd));
-  return pd;
+  /* Copy CR3, the page directory base register (PDBR), into
+     `pd'.
+     See [IA32-v2a] "MOV--Move to/from Control Registers" and
+     [IA32-v3] 3.7.5. */
+  uintptr_t pd;
+  asm ("mov %0, %%cr3" : "=r" (pd));
+  return ptov (pd);
 }