[PATCH 3.15 01/42] powerpc/perf: Fix MMCR2 handling for EBB

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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

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

From: Michael Ellerman <mpe@ellerman.id.au>

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@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/powerpc/perf/core-book3s.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -1307,6 +1307,9 @@ static void power_pmu_enable(struct pmu
  out_enable:
 	pmao_restore_workaround(ebb);
 
+	if (ppmu->flags & PPMU_ARCH_207S)
+		mtspr(SPRN_MMCR2, 0);
+
 	mmcr0 = ebb_switch_in(ebb, cpuhw->mmcr[0]);
 
 	mb();
@@ -1315,9 +1318,6 @@ static void power_pmu_enable(struct pmu
 
 	write_mmcr0(cpuhw, mmcr0);
 
-	if (ppmu->flags & PPMU_ARCH_207S)
-		mtspr(SPRN_MMCR2, 0);
-
 	/*
 	 * Enable instruction sampling if necessary
 	 */