[TRIVIAL] Re: document unused pte bits on i386

[TRIVIAL] Re: document unused pte bits on i386

[Rusty Trivial Russell]

From:  Ed L Cashin <ecashin@uga.edu>

  Ed L Cashin <ecashin@uga.edu> writes:
  
  > Hi.  This small patch documents that bits 9, 10, and 11 are unused by
  > the Linux kernel.  The IA-32 Intel Architecture Software Developer's
  > Manual says that these bits are available for programmer use.
  >
  > I checked and couldn't see any use of these bits in the Linux kernel.
  > If I'm wrong and these bits *are* being used by the linux kernel, a
  > comment in include/asm-i386/pgtable.h would be helpful.  If they are
  > not, this patch confirms for developers that the kernel isn't using
  > these bits.
  
  For consistency, there should be the analogous _PAGE_BIT_XXX macros,
  too, so here's a replacement patch that has those.
  
  

--- trivial-2.6.0-test5-bk10/include/asm-i386/pgtable.h.orig	2003-09-24 12:27:18.000000000 +1000
+++ trivial-2.6.0-test5-bk10/include/asm-i386/pgtable.h	2003-09-24 12:27:18.000000000 +1000
@@ -108,6 +108,9 @@
 #define _PAGE_BIT_DIRTY		6
 #define _PAGE_BIT_PSE		7	/* 4 MB (or 2MB) page, Pentium+, if present.. */
 #define _PAGE_BIT_GLOBAL	8	/* Global TLB entry PPro+ */
+#define _PAGE_BIT_UNUSED1	9	/* available for programmer */
+#define _PAGE_BIT_UNUSED2	10
+#define _PAGE_BIT_UNUSED3	11
 
 #define _PAGE_PRESENT	0x001
 #define _PAGE_RW	0x002
@@ -118,6 +121,9 @@
 #define _PAGE_DIRTY	0x040
 #define _PAGE_PSE	0x080	/* 4 MB (or 2MB) page, Pentium+, if present.. */
 #define _PAGE_GLOBAL	0x100	/* Global TLB entry PPro+ */
+#define _PAGE_UNUSED1	0x200	/* available for programmer */
+#define _PAGE_UNUSED2	0x400
+#define _PAGE_UNUSED3	0x800
 
 #define _PAGE_FILE	0x040	/* set:pagecache unset:swap */
 #define _PAGE_PROTNONE	0x080	/* If not present */
-- 
  What is this? http://www.kernel.org/pub/linux/kernel/people/rusty/trivial/
  Don't blame me: the Monkey is driving
  File: Ed L Cashin <ecashin@uga.edu>: Re: [TRIVIAL][PATCH] document unused pte bits on i386