perf, powerpc: Handle events that raise an exception without overflowing

Events on POWER7 can roll back if a speculative event doesn't
eventually complete. Unfortunately in some rare cases they will
raise a performance monitor exception. We need to catch this to
ensure we reset the PMC. In all cases the PMC will be 256 or less
cycles from overflow.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <stable@kernel.org> # as far back as it applies cleanly
LKML-Reference: <20110309143842.6c22845e@kryten>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
static int collect_events(struct perf_event *group, int max_count,
			  struct perf_event *ctrs[], u64 *events,
			  unsigned int *flags)
{
	int n = 0;
	struct perf_event *event;

	if (!is_software_event(group)) {
		if (n >= max_count)
			return -1;
		ctrs[n] = group;
		flags[n] = group->hw.event_base;
		events[n++] = group->hw.config;
	}
	list_for_each_entry(event, &group->sibling_list, group_entry) {
		if (!is_software_event(event) &&
		    event->state != PERF_EVENT_STATE_OFF) {
			if (n >= max_count)
				return -1;
			ctrs[n] = event;
			flags[n] = event->hw.event_base;
			events[n++] = event->hw.config;
		}
	}
	return n;
}

static int collect_events(struct perf_event *group, int max_count,
			  struct perf_event *ctrs[], u64 *events,
			  unsigned int *flags)
{
	int n = 0;
	struct perf_event *event;

	if (!is_software_event(group)) {
		if (n >= max_count)
			return -1;
		ctrs[n] = group;
		flags[n] = group->hw.event_base;
		events[n++] = group->hw.config;
	}
	list_for_each_entry(event, &group->sibling_list, group_entry) {
		if (!is_software_event(event) &&
		    event->state != PERF_EVENT_STATE_OFF) {
			if (n >= max_count)
				return -1;
			ctrs[n] = event;
			flags[n] = event->hw.event_base;
			events[n++] = event->hw.config;
		}
	}
	return n;
}
