[tip:perf/urgent] x86/perf: Fix CR4.PCE propagation to use active_mm instead of mm

[tip-bot for Andy Lutomirski <tipbot@zytor.com>]

Commit-ID:  5dc855d44c2ad960a86f593c60461f1ae1566b6d
Gitweb:     http://git.kernel.org/tip/5dc855d44c2ad960a86f593c60461f1ae1566b6d
Author:     Andy Lutomirski <luto@kernel.org>
AuthorDate: Thu, 16 Mar 2017 12:59:39 -0700
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 17 Mar 2017 08:28:26 +0100

x86/perf: Fix CR4.PCE propagation to use active_mm instead of mm

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.

Reported-and-tested-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Fixes: 7911d3f7af14 ("perf/x86: Only allow rdpmc if a perf_event is mapped")
Link: http://lkml.kernel.org/r/0c5b38a76ea50e405f9abe07a13dfaef87c173a1.1489694270.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@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 1635c0c..e07b36c 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2100,8 +2100,8 @@ 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)