powerpc/book3s: Fix CFAR clobbering issue in machine check handler.

While checking powersaving mode in machine check handler at 0x200, we
clobber CFAR register. Fix it by saving and restoring it during beq/bgt.

Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

2 files changed, 13 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/exception-64s.h b/arch/powerpc/include/asm/exception-64s.h
index 66830618cc19..aeaa56cd9b54 100644
--- a/arch/powerpc/include/asm/exception-64s.h
+++ b/arch/powerpc/include/asm/exception-64s.h
@@ -147,6 +147,14 @@ BEGIN_FTR_SECTION_NESTED(943)						\
 END_FTR_SECTION_NESTED(ftr,ftr,943)
 
 /*
+ * Set an SPR from a register if the CPU has the given feature
+ */
+#define OPT_SET_SPR(ra, spr, ftr)                                       \
+BEGIN_FTR_SECTION_NESTED(943)                                           \
+        mtspr   spr,ra;                                                 \
+END_FTR_SECTION_NESTED(ftr,ftr,943)
+
+/*
  * Save a register to the PACA if the CPU has the given feature
  */
 #define OPT_SAVE_REG_TO_PACA(offset, ra, ftr)                           \
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 38d507306a11..4c34c3c827ad 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -164,13 +164,18 @@ BEGIN_FTR_SECTION
          */
         mfspr   r13,SPRN_SRR1
         rlwinm. r13,r13,47-31,30,31
+        OPT_GET_SPR(r13, SPRN_CFAR, CPU_FTR_CFAR)
         beq     9f
 
+        mfspr   r13,SPRN_SRR1
+        rlwinm. r13,r13,47-31,30,31
         /* waking up from powersave (nap) state */
         cmpwi   cr1,r13,2
         /* Total loss of HV state is fatal. let's just stay stuck here */
+        OPT_GET_SPR(r13, SPRN_CFAR, CPU_FTR_CFAR)
         bgt     cr1,.
 9:
+        OPT_SET_SPR(r13, SPRN_CFAR, CPU_FTR_CFAR)
 END_FTR_SECTION_IFSET(CPU_FTR_HVMODE | CPU_FTR_ARCH_206)
 #endif /* CONFIG_PPC_P7_NAP */
         EXCEPTION_PROLOG_0(PACA_EXMC)