[PATCH 3.11 084/137] powerpc/perf: Fix MMCR2 handling for EBB

[Luis Henriques]

3.11.10.15 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Michael Ellerman <mpe@xxxxxxxxxxxxxx>

commit 8903461c9bc56fcb041fb92d054e2529951770b6 upstream.

In the recent commit b50a6c584bb4 "Clear MMCR2 when enabling PMU", I
screwed up the handling of MMCR2 for tasks using EBB.

We must make sure we set MMCR2 *before* ebb_switch_in(), otherwise we
overwrite the value of MMCR2 that userspace may have written. That
potentially breaks a task that uses EBB and manually uses MMCR2 for
event freezing.

Fixes: b50a6c584bb4 ("powerpc/perf: Clear MMCR2 when enabling PMU")
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
[ luis: backported to 3.11: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
 arch/powerpc/perf/core-book3s.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index c05f10e95a9e..d5d7adf6dc50 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -1159,14 +1159,14 @@ static void power_pmu_enable(struct pmu *pmu)
 	cpuhw->mmcr[0] |= MMCR0_PMXE | MMCR0_FCECE;
 
  out_enable:
+	if (ppmu->flags & PPMU_ARCH_207S)
+		mtspr(SPRN_MMCR2, 0);
+
 	mmcr0 = ebb_switch_in(ebb, cpuhw->mmcr[0]);
 
 	mb();
 	write_mmcr0(cpuhw, mmcr0);
 
-	if (ppmu->flags & PPMU_ARCH_207S)
-		mtspr(SPRN_MMCR2, 0);
-
 	/*
 	 * Enable instruction sampling if necessary
 	 */
-- 
1.9.1

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