On Fri, Mar 12, 2021 at 05:21:37AM -0800, kan.li...@linux.intel.com wrote: > From: Kan Liang <kan.li...@linux.intel.com> > > A repeatable crash can be triggered by the perf_fuzzer on some Haswell > system. > https://lore.kernel.org/lkml/7170d3b-c17f-1ded-52aa-cc6d9ae99...@maine.edu/ > > For some old CPUs (HSW and earlier), the PEBS status in a PEBS record > may be mistakenly set to 0. To minimize the impact of the defect, the > commit was introduced to try to avoid dropping the PEBS record for some > cases. It adds a check in the intel_pmu_drain_pebs_nhm(), and updates > the local pebs_status accordingly. However, it doesn't correct the PEBS > status in the PEBS record, which may trigger the crash, especially for > the large PEBS. > > It's possible that all the PEBS records in a large PEBS have the PEBS > status 0. If so, the first get_next_pebs_record_by_bit() in the > __intel_pmu_pebs_event() returns NULL. The at = NULL. Since it's a large > PEBS, the 'count' parameter must > 1. The second > get_next_pebs_record_by_bit() will crash. > > Besides the local pebs_status, correct the PEBS status in the PEBS > record as well. > > Fixes: 01330d7288e0 ("perf/x86: Allow zero PEBS status with only single > active event") > Reported-by: Vince Weaver <vincent.wea...@maine.edu> > Suggested-by: Peter Zijlstra (Intel) <pet...@infradead.org> > Signed-off-by: Kan Liang <kan.li...@linux.intel.com> > Cc: sta...@vger.kernel.org
Tested-by: Namhyung Kim <namhy...@kernel.org> Thanks, Namhyung > --- > arch/x86/events/intel/ds.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c > index 7ebae18..bcf4fa5 100644 > --- a/arch/x86/events/intel/ds.c > +++ b/arch/x86/events/intel/ds.c > @@ -2010,7 +2010,7 @@ static void intel_pmu_drain_pebs_nhm(struct pt_regs > *iregs, struct perf_sample_d > */ > if (!pebs_status && cpuc->pebs_enabled && > !(cpuc->pebs_enabled & (cpuc->pebs_enabled-1))) > - pebs_status = cpuc->pebs_enabled; > + pebs_status = p->status = cpuc->pebs_enabled; > > bit = find_first_bit((unsigned long *)&pebs_status, > x86_pmu.max_pebs_events); > -- > 2.7.4 >
