powerpc: Fix oops when loading modules

This fixes a problem reported by Sean MacLennan where loading any
module would cause an oops.  We weren't marking the pages containing
the module text as having hardware execute permission, due to a bug
introduced in commit 8d1cf34e ("powerpc/mm: Tweak PTE bit combination
definitions"), hence trying to execute the module text caused an
exception on processors that support hardware execute permission.

This adds _PAGE_HWEXEC to the definitions of PAGE_KERNEL_X and
PAGE_KERNEL_ROX to fix this problem.
Reported-by: Sean MacLennan <smaclennan@pikatech.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/include/asm/pte-common.h

@@ -151,9 +151,11 @@ extern unsigned long bad_call_to_PMD_PAGE_SIZE(void);
 				 _PAGE_NO_CACHE)
 #define PAGE_KERNEL_NCG	__pgprot(_PAGE_BASE_NC | _PAGE_KERNEL_RW | \
 				 _PAGE_NO_CACHE | _PAGE_GUARDED)
-#define PAGE_KERNEL_X	__pgprot(_PAGE_BASE | _PAGE_KERNEL_RW | _PAGE_EXEC)
+#define PAGE_KERNEL_X	__pgprot(_PAGE_BASE | _PAGE_KERNEL_RW | _PAGE_EXEC | \
+				 _PAGE_HWEXEC)
 #define PAGE_KERNEL_RO	__pgprot(_PAGE_BASE | _PAGE_KERNEL_RO)
-#define PAGE_KERNEL_ROX	__pgprot(_PAGE_BASE | _PAGE_KERNEL_RO | _PAGE_EXEC)
+#define PAGE_KERNEL_ROX	__pgprot(_PAGE_BASE | _PAGE_KERNEL_RO | _PAGE_EXEC | \
+				 _PAGE_HWEXEC)
 
 /* Protection used for kernel text. We want the debuggers to be able to
  * set breakpoints anywhere, so don't write protect the kernel text