[SPARC64]: Reserve a software PTE bit for _PAGE_EXEC.

Based upon the PAX sparc64 patches.  Credit to
PaX Team <pageexec@freemail.hu>

Also, reformat the comments here so the lines fit in
80 columns.
Signed-off-by: David S. Miller <davem@redhat.com>

include/asm-sparc64/pgtable.h

@@ -107,7 +107,7 @@
 
 /* Spitfire/Cheetah TTE bits. */
 #define _PAGE_VALID	_AC(0x8000000000000000,UL) /* Valid TTE              */
-#define _PAGE_R		_AC(0x8000000000000000,UL) /* Keep ref bit up to date */
+#define _PAGE_R		_AC(0x8000000000000000,UL) /* Keep ref bit up to date*/
 #define _PAGE_SZ4MB	_AC(0x6000000000000000,UL) /* 4MB Page               */
 #define _PAGE_SZ512K	_AC(0x4000000000000000,UL) /* 512K Page              */
 #define _PAGE_SZ64K	_AC(0x2000000000000000,UL) /* 64K Page               */
@@ -118,8 +118,8 @@
 #define _PAGE_RES1	_AC(0x0003000000000000,UL) /* Reserved               */
 #define _PAGE_SN	_AC(0x0000800000000000,UL) /* (Cheetah) Snoop        */
 #define _PAGE_RES2	_AC(0x0000780000000000,UL) /* Reserved               */
-#define _PAGE_PADDR_SF	_AC(0x000001FFFFFFE000,UL) /* (Spitfire) paddr [40:13]*/
-#define _PAGE_PADDR	_AC(0x000007FFFFFFE000,UL) /* (Cheetah) paddr [42:13] */
+#define _PAGE_PADDR_SF	_AC(0x000001FFFFFFE000,UL) /* (Spitfire) paddr[40:13]*/
+#define _PAGE_PADDR	_AC(0x000007FFFFFFE000,UL) /* (Cheetah) paddr[42:13] */
 #define _PAGE_SOFT	_AC(0x0000000000001F80,UL) /* Software bits          */
 #define _PAGE_L		_AC(0x0000000000000040,UL) /* Locked TTE             */
 #define _PAGE_CP	_AC(0x0000000000000020,UL) /* Cacheable in P-Cache   */
@@ -129,9 +129,22 @@
 #define _PAGE_W		_AC(0x0000000000000002,UL) /* Writable               */
 #define _PAGE_G		_AC(0x0000000000000001,UL) /* Global                 */
 
-/* Here are the SpitFire software bits we use in the TTE's. */
-#define _PAGE_FILE	_AC(0x0000000000001000,UL)	/* Pagecache page     */
+/* Here are the SpitFire software bits we use in the TTE's.
+ *
+ * WARNING: If you are going to try and start using some
+ *          of the soft2 bits, you will need to make
+ *          modifications to the swap entry implementation.
+ *	    For example, one thing that could happen is that
+ *          swp_entry_to_pte() would BUG_ON() if you tried
+ *          to use one of the soft2 bits for _PAGE_FILE.
+ *
+ * Like other architectures, I have aliased _PAGE_FILE with
+ * _PAGE_MODIFIED.  This works because _PAGE_FILE is never
+ * interpreted that way unless _PAGE_PRESENT is clear.
+ */
+#define _PAGE_EXEC	_AC(0x0000000000001000,UL)	/* Executable SW bit */
 #define _PAGE_MODIFIED	_AC(0x0000000000000800,UL)	/* Modified (dirty)  */
+#define _PAGE_FILE	_AC(0x0000000000000800,UL)	/* Pagecache page    */
 #define _PAGE_ACCESSED	_AC(0x0000000000000400,UL)	/* Accessed (ref'd)  */
 #define _PAGE_READ	_AC(0x0000000000000200,UL)	/* Readable SW Bit   */
 #define _PAGE_WRITE	_AC(0x0000000000000100,UL)	/* Writable SW Bit   */