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>
void power_pmu_start_txn(struct pmu *pmu)
{
	struct cpu_hw_events *cpuhw = &__get_cpu_var(cpu_hw_events);

	perf_pmu_disable(pmu);
	cpuhw->group_flag |= PERF_EVENT_TXN;
	cpuhw->n_txn_start = cpuhw->n_events;
}

void power_pmu_start_txn(struct pmu *pmu)
{
	struct cpu_hw_events *cpuhw = &__get_cpu_var(cpu_hw_events);

	perf_pmu_disable(pmu);
	cpuhw->group_flag |= PERF_EVENT_TXN;
	cpuhw->n_txn_start = cpuhw->n_events;
}
