[PATCH 1/2] x86/perf: Fix CR4.PCE propagation to use active_mm instead of mm

[Andy Lutomirski]

If one thread mmaps a perf event while another thread in the same mm
is in some context where active_mm != mm (which can happen in the
scheduler, for example), refresh_pce() would write the wrong value
to CR4.PCE.  This broke some PAPI tests.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 7911d3f7af14 ("perf/x86: Only allow rdpmc if a perf_event is mapped")
Reported-and-tested-by: Vince Weaver <vincent.weaver@xxxxxxxxx>
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
---
 arch/x86/events/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 349d4d17aa7f..4f564df73b8f 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2101,8 +2101,8 @@ static int x86_pmu_event_init(struct perf_event *event)
 
 static void refresh_pce(void *ignored)
 {
-	if (current->mm)
-		load_mm_cr4(current->mm);
+	if (current->active_mm)
+		load_mm_cr4(current->active_mm);
 }
 
 static void x86_pmu_event_mapped(struct perf_event *event)
-- 
2.9.3