[PATCH][Zesty] UBUNTU: SAUCE: powerpc: Invalidate ERAT on powersave wakeup for POWER9

[Breno Leitao]

From: Michael Neuling <mikey at neuling.org>

BugLink: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1700521

On POWER9 the ERAT may be incorrect on wakeup from some stop states
that lose state. This causes random segvs and illegal instructions
when these stop states are enabled.

This patch invalidates the ERAT on wakeup on POWER9 to prevent this
from causing a problem.

Signed-off-by: Michael Neuling <mikey at neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>
(backported from: https://patchwork.ozlabs.org/patch/780365/)
Signed-off-by: Breno Leitao <leitao at debian.org>
---
 arch/powerpc/kernel/exceptions-64s.S | 4 +++-
 arch/powerpc/kernel/idle_book3s.S    | 7 +++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index f2a18432253c..3ee66dd600fc 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -99,7 +99,9 @@ EXC_VIRT_NONE(0x4000, 0x4100)
 #ifdef CONFIG_PPC_P7_NAP
 	/*
 	 * If running native on arch 2.06 or later, check if we are waking up
-	 * from nap/sleep/winkle, and branch to idle handler.
+	 * from nap/sleep/winkle, and branch to idle handler. This tests
+	 * SRR1 bits 46:47. A non-0 value indicates that we are coming from
+	 * a power saving state.
 	 */
 #define IDLETEST(n)							\
 	BEGIN_FTR_SECTION ;						\
diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S
index 67ba6a66fed5..fb762ee5ac6f 100644
--- a/arch/powerpc/kernel/idle_book3s.S
+++ b/arch/powerpc/kernel/idle_book3s.S
@@ -433,6 +433,13 @@ FTR_SECTION_ELSE_NESTED(70)
 	ld	r2, PACATOC(r13)
 ALT_FTR_SECTION_END_NESTED_IFSET(CPU_FTR_POWER9_DD1, 70)
 	/*
+	 * Workaround for POWER9, if we lost resources, the ERAT
+	 * might have been mixed up and needs flushing.
+	 */
+	blt	cr3,1f
+	PPC_INVALIDATE_ERAT
+1:
+	/*
 	 * POWER ISA 3. Use PSSCR to determine if we
 	 * are waking up from deep idle state
 	 */
-- 
2.11.0