From: Alexander Shishkin alexander.shishkin@linux.intel.com
[ Upstream commit 92ca7da4bdc24d63bb0bcd241c11441ddb63b80a ]
Commit:
ccbebba4c6bf ("perf/x86/intel/pt: Bypass PT vs. LBR exclusivity if the core supports it")
skips the PT/LBR exclusivity check on CPUs where PT and LBRs coexist, but also inadvertently skips the active_events bump for PT in that case, which is a bug. If there aren't any hardware events at the same time as PT, the PMI handler will ignore PT PMIs, as active_events reads zero in that case, resulting in the "Uhhuh" spurious NMI warning and PT data loss.
Fix this by always increasing active_events for PT events.
Fixes: ccbebba4c6bf ("perf/x86/intel/pt: Bypass PT vs. LBR exclusivity if the core supports it") Reported-by: Vitaly Slobodskoy vitaly.slobodskoy@intel.com Signed-off-by: Alexander Shishkin alexander.shishkin@linux.intel.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Acked-by: Alexey Budankov alexey.budankov@linux.intel.com Cc: Jiri Olsa jolsa@kernel.org Cc: Ingo Molnar mingo@redhat.com Cc: Arnaldo Carvalho de Melo acme@redhat.com Link: https://lkml.kernel.org/r/20191210105101.77210-1-alexander.shishkin@linux.in... Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/events/core.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index 6ed99de2ddf5..c1f7b3cb84a9 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -375,7 +375,7 @@ int x86_add_exclusive(unsigned int what) * LBR and BTS are still mutually exclusive. */ if (x86_pmu.lbr_pt_coexist && what == x86_lbr_exclusive_pt) - return 0; + goto out;
if (!atomic_inc_not_zero(&x86_pmu.lbr_exclusive[what])) { mutex_lock(&pmc_reserve_mutex); @@ -387,6 +387,7 @@ int x86_add_exclusive(unsigned int what) mutex_unlock(&pmc_reserve_mutex); }
+out: atomic_inc(&active_events); return 0;
@@ -397,11 +398,15 @@ int x86_add_exclusive(unsigned int what)
void x86_del_exclusive(unsigned int what) { + atomic_dec(&active_events); + + /* + * See the comment in x86_add_exclusive(). + */ if (x86_pmu.lbr_pt_coexist && what == x86_lbr_exclusive_pt) return;
atomic_dec(&x86_pmu.lbr_exclusive[what]); - atomic_dec(&active_events); }
int x86_setup_perfctr(struct perf_event *event)