powerpc/64s: Exception macro for stack frame and initial register save

This code is common to a few exceptions, and another user will be added.
This causes a trivial change to generated code:

-     604: std     r9,416(r1)
-     608: mfspr   r11,314
-     60c: std     r11,368(r1)
-     610: mfspr   r12,315
+     604: mfspr   r11,314
+     608: mfspr   r12,315
+     60c: std     r9,416(r1)
+     610: std     r11,368(r1)

machine_check_powernv_early could also use this, but that requires non
trivial changes to generated code, so that's for another patch.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/exception-64s.h

@@ -323,6 +323,15 @@ END_FTR_SECTION_NESTED(ftr,ftr,943)
 
 #define NOTEST(n)
 
+#define EXCEPTION_PROLOG_COMMON_1()					   \
+	std	r9,_CCR(r1);		/* save CR in stackframe	*/ \
+	std	r11,_NIP(r1);		/* save SRR0 in stackframe	*/ \
+	std	r12,_MSR(r1);		/* save SRR1 in stackframe	*/ \
+	std	r10,0(r1);		/* make stack chain pointer	*/ \
+	std	r0,GPR0(r1);		/* save r0 in stackframe	*/ \
+	std	r10,GPR1(r1);		/* save r1 in stackframe	*/ \
+
+
 /*
  * The common exception prolog is used for all except a few exceptions
  * such as a segment miss on a kernel address.  We have to be prepared
@@ -347,12 +356,7 @@ END_FTR_SECTION_NESTED(ftr,ftr,943)
 	addi	r3,r13,area;		/* r3 -> where regs are saved*/	   \
 	RESTORE_CTR(r1, area);						   \
 	b	bad_stack;						   \
-3:	std	r9,_CCR(r1);		/* save CR in stackframe	*/ \
-	std	r11,_NIP(r1);		/* save SRR0 in stackframe	*/ \
-	std	r12,_MSR(r1);		/* save SRR1 in stackframe	*/ \
-	std	r10,0(r1);		/* make stack chain pointer	*/ \
-	std	r0,GPR0(r1);		/* save r0 in stackframe	*/ \
-	std	r10,GPR1(r1);		/* save r1 in stackframe	*/ \
+3:	EXCEPTION_PROLOG_COMMON_1();					   \
 	beq	4f;			/* if from kernel mode		*/ \
 	ACCOUNT_CPU_USER_ENTRY(r13, r9, r10);				   \
 	SAVE_PPR(area, r9, r10);					   \

arch/powerpc/kernel/exceptions-64s.S

@@ -930,16 +930,11 @@ TRAMP_KVM_HV(PACA_EXGEN, 0xe60)
 TRAMP_REAL_BEGIN(hmi_exception_early)
 	EXCEPTION_PROLOG_1(PACA_EXGEN, KVMTEST_HV, 0xe60)
 	mr	r10,r1			/* Save r1 */
-	ld	r1,PACAEMERGSP(r13)	/* Use emergency stack		*/
+	ld	r1,PACAEMERGSP(r13)	/* Use emergency stack for realmode */
 	subi	r1,r1,INT_FRAME_SIZE	/* alloc stack frame		*/
-	std	r9,_CCR(r1)		/* save CR in stackframe	*/
 	mfspr	r11,SPRN_HSRR0		/* Save HSRR0 */
-	std	r11,_NIP(r1)		/* save HSRR0 in stackframe	*/
-	mfspr	r12,SPRN_HSRR1		/* Save SRR1 */
-	std	r12,_MSR(r1)		/* save SRR1 in stackframe	*/
-	std	r10,0(r1)		/* make stack chain pointer	*/
-	std	r0,GPR0(r1)		/* save r0 in stackframe	*/
-	std	r10,GPR1(r1)		/* save r1 in stackframe	*/
+	mfspr	r12,SPRN_HSRR1		/* Save HSRR1 */
+	EXCEPTION_PROLOG_COMMON_1()
 	EXCEPTION_PROLOG_COMMON_2(PACA_EXGEN)
 	EXCEPTION_PROLOG_COMMON_3(0xe60)
 	addi	r3,r1,STACK_FRAME_OVERHEAD