Subject: [PATCH v2 46/52] powerpc/64s/exception: fix machine check early should not set AMR

From: Nicholas Piggin <[email-masked]>
Date: Thu, 20 Jun 2019 15:14:53 +1000

The early machine check runs in real mode, so locking is unnecessary.
Worse, the windup does not restore AMR, so this can result in a false
KUAP fault after a recoverable machine check hits inside a user copy
operation.

Fix this similarly to HMI by just avoiding the kuap lock in the
early machine check handler (it will be set by the late handler that
runs in virtual mode if that runs).

Fixes: 890274c2dc4c0 ("powerpc/64s: Implement KUAP for Radix MMU")
Signed-off-by: Nicholas Piggin <[email-masked]>
---
 arch/powerpc/kernel/exceptions-64s.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index ab22af2509d8..8ed787dc579c 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -1012,7 +1012,7 @@ TRAMP_REAL_BEGIN(machine_check_common_early)
 	mfspr	r11,SPRN_DSISR		/* Save DSISR */
 	std	r11,_DSISR(r1)
 	std	r9,_CCR(r1)		/* Save CR in stackframe */
-	kuap_save_amr_and_lock r9, r10, cr1
+	/* We don't touch AMR here, we never go to virtual mode */
 	/* Save r9 through r13 from EXMC save area to stack frame. */
 	EXCEPTION_PROLOG_COMMON_2(PACA_EXMC)
 	mfmsr	r11			/* get MSR value */
-- 
2.20.1