X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=src%2Fuserprog%2Fpagedir.c;h=3f0e9fb47c1217c8bbe0266f8a5b6b7a9e130e0e;hb=47fcd26fa98f931f15e5961998b2437e2789f8b3;hp=937f433da030505e701d00f7a9bb8a15feb49dcb;hpb=c2e63e6e7f14d2ce25791aeff2ef592a4cd51663;p=pintos-anon

diff --git a/src/userprog/pagedir.c b/src/userprog/pagedir.c
index 937f433..3f0e9fb 100644
--- a/src/userprog/pagedir.c
+++ b/src/userprog/pagedir.c
@@ -187,6 +187,11 @@ pagedir_activate (uint32_t *pd)
 {
   if (pd == NULL)
     pd = base_page_dir;
+
+  /* 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 ("movl %0,%%cr3" :: "r" (vtop (pd)));
 }
 
@@ -196,6 +201,9 @@ active_pd (void)
 {
   uint32_t *pd;
 
+  /* Copy CR3, the page directory base register (PDBR), into `pd'
+     for us to examine.  See [IA32-v2a] "MOV--Move to/from
+     Control Registers" and [IA32-v3] 3.7.5. */
   asm ("movl %%cr3,%0" : "=r" (pd));
   return pd;
 }