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

From: Andy Lutomirski <luto@kernel.org>
To: X86 ML <x86@kernel.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Borislav Petkov <bpetkov@suse.de>,
	Vince Weaver <vincent.weaver@maine.edu>,
	Andy Lutomirski <luto@kernel.org>,
	stable@vger.kernel.org
Subject: [PATCH 1/2] x86/perf: Fix CR4.PCE propagation to use active_mm instead of mm
Date: Thu, 16 Mar 2017 12:59:39 -0700
Message-ID: <0c5b38a76ea50e405f9abe07a13dfaef87c173a1.1489694270.git.luto@kernel.org> (raw)
In-Reply-To: <cover.1489694270.git.luto@kernel.org>
In-Reply-To: <cover.1489694270.git.luto@kernel.org>

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
