powerpc/kprobes: Some minor fixes

* Mark __flush_icache_range as a function that can't be probed since its
used by the kprobe code.

* Fix an issue with single stepping and async exceptions. We need to
ensure that we dont get an async exception (external, decrementer, etc)
while we are attempting to single step the probe point.

Added a check to ensure we only handle a single step if its really
intended for the instruction in question.

Signed-off-by: Kumar Gala <[e-mail]>

arch/powerpc/kernel/kprobes.c

···
 
 static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
 {
+	/* We turn off async exceptions to ensure that the single step will
+	 * be for the instruction we have the kprobe on, if we dont its
+	 * possible we'd get the single step reported for an exception handler
+	 * like Decrementer or External Interrupt */
+	regs->msr &= ~MSR_EE;
 	regs->msr |= MSR_SE;
 
 	/*
···
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 
 	if (!cur)
+		return 0;
+
+	/* make sure we got here for instruction we have a kprobe on */
+	if (((unsigned long)cur->ainsn.insn + 4) != regs->nip)
 		return 0;
 
 	if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {

arch/powerpc/kernel/misc_32.S

···
  *
  * flush_icache_range(unsigned long start, unsigned long stop)
  */
-_GLOBAL(__flush_icache_range)
+_KPROBE(__flush_icache_range)
 BEGIN_FTR_SECTION
 	blr				/* for 601, do nothing */
 END_FTR_SECTION_IFSET(CPU_FTR_COHERENT_ICACHE)