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SubjectRe: [TRIVIAL][PATCH] document unused pte bits on i386
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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 */

--
--Ed L Cashin | PGP public key:
ecashin@uga.edu | http://noserose.net/e/pgp/
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