Re: [TRIVIAL][PATCH] document unused pte bits on i386

[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.


--- linux-2.6.0-test2/include/asm-i386/pgtable.h~	Sun Jul 27 13:06:27 2003
+++ linux-2.6.0-test2/include/asm-i386/pgtable.h	Thu Aug  7 11:38:17 2003
@@ -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 */


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