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

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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@vger.kernel.org
Fixes: 7911d3f7af14 ("perf/x86: Only allow rdpmc if a perf_event is mapped")
Reported-and-tested-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 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

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[PATCH 0/2] x86/perf: A CR4.PCE bugfix and clarification Andy Lutomirski <luto@kernel.org> - 2017-03-16 21:10 +0100
  [PATCH 1/2] x86/perf: Fix CR4.PCE propagation to use active_mm instead of mm Andy Lutomirski <luto@kernel.org> - 2017-03-16 21:10 +0100
    [tip:perf/urgent] x86/perf: Fix CR4.PCE propagation to use  active_mm instead of mm tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2017-03-17 11:50 +0100
  [PATCH 2/2] x86/perf: Clarify why x86_pmu_event_mapped() isn't racy Andy Lutomirski <luto@kernel.org> - 2017-03-16 21:10 +0100
    [tip:perf/urgent] x86/perf: Clarify why x86_pmu_event_mapped()  isn't racy tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2017-03-17 11:50 +0100

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