powerpc/64s/exception: Fix machine check early corrupting AMR

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). If the virtual mode handler is
reached, it will lock and restore the AMR.

Fixes: 890274c2dc4c0 ("powerpc/64s: Implement KUAP for Radix MMU")
Cc: Russell Currey <ruscur@russell.cc>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 6b86055e5251f26b030dbb1c656bc09a8e5fb48e..73ba246ca11d2b12d6abe6fe28449190160e00de 100644 (file)
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -315,7 +315,7 @@ 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 */