hw-breakpoints, perf: Fix broken mmiotrace due to dr6 by reference change

Commit 62edab9056a6cf0c9207339c8892c923a5217e45 (from June 2009
but merged in 2.6.33) changes notify_die to pass dr6 by
reference.

However, it forgets to fix the check for DR_STEP in kmmio.c,
breaking mmiotrace. It also passes a wrong value to the post
handler.

This simple fix makes mmiotrace work again.

Signed-off-by: Luca Barbieri <luca@luca-barbieri.com>
Acked-by: K.Prasad <prasad@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1263634770-14578-1-git-send-email-luca@luca-barbieri.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/mm/kmmio.c

@@ -538,14 +538,15 @@ static int
 kmmio_die_notifier(struct notifier_block *nb, unsigned long val, void *args)
 {
 	struct die_args *arg = args;
+	unsigned long* dr6_p = (unsigned long *)ERR_PTR(arg->err);
 
-	if (val == DIE_DEBUG && (arg->err & DR_STEP))
-		if (post_kmmio_handler(arg->err, arg->regs) == 1) {
+	if (val == DIE_DEBUG && (*dr6_p & DR_STEP))
+		if (post_kmmio_handler(*dr6_p, arg->regs) == 1) {
 			/*
 			 * Reset the BS bit in dr6 (pointed by args->err) to
 			 * denote completion of processing
 			 */
-			(*(unsigned long *)ERR_PTR(arg->err)) &= ~DR_STEP;
+			*dr6_p &= ~DR_STEP;
 			return NOTIFY_STOP;
 		}