powerpc/64s/exception: simplify hmi control flow

Branch to the relocated 0xc000 address early (still in real mode), to
simplify subsequent branches. Have the virt mode handler avoid just
'windup' and redo the exception from scratch, rather than branching
back to the trampoline.

Rearrange the stack setup instruction location to match the system
reset handler (e.g., right before EXCEPTION_PROLOG_COMMON).

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

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

@@ -260,17 +260,6 @@ END_FTR_SECTION_NESTED(ftr,ftr,943)
 	mtctr	reg;							\
 	bctr
 
-#ifdef CONFIG_RELOCATABLE
-#define BRANCH_LINK_TO_FAR(label)					\
-	__LOAD_FAR_HANDLER(r12, label);					\
-	mtctr	r12;							\
-	bctrl
-
-#else
-#define BRANCH_LINK_TO_FAR(label)					\
-	bl	label
-#endif
-
 #ifdef CONFIG_KVM_BOOK3S_64_HANDLER
 #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
 /*
@@ -1713,22 +1702,26 @@ EXC_REAL_BEGIN(hmi_exception, 0xe60, 0x20)
 	EXCEPTION_PROLOG_0 PACA_EXGEN
 	b	hmi_exception_early
 EXC_REAL_END(hmi_exception, 0xe60, 0x20)
-__TRAMP_REAL_OOL_MASKABLE_HV(hmi_exception, 0xe60, IRQS_DISABLED)
 EXC_VIRT_NONE(0x4e60, 0x20)
 TRAMP_KVM_HV(PACA_EXGEN, 0xe60)
 TRAMP_REAL_BEGIN(hmi_exception_early)
 	EXCEPTION_PROLOG_1 EXC_HV, PACA_EXGEN, 1, 0xe60, 0, 0, 0
+	mfctr	r10			/* save ctr, even for !RELOCATABLE */
+	BRANCH_TO_C000(r11, hmi_exception_early_common)
+
+EXC_COMMON_BEGIN(hmi_exception_early_common)
+	mtctr	r10			/* Restore ctr */
+	mfspr	r11,SPRN_HSRR0		/* Save HSRR0 */
+	mfspr	r12,SPRN_HSRR1		/* Save HSRR1 */
 	mr	r10,r1			/* Save r1 */
 	ld	r1,PACAEMERGSP(r13)	/* Use emergency stack for realmode */
 	subi	r1,r1,INT_FRAME_SIZE	/* alloc stack frame		*/
-	mfspr	r11,SPRN_HSRR0		/* Save HSRR0 */
-	mfspr	r12,SPRN_HSRR1		/* Save HSRR1 */
 	EXCEPTION_PROLOG_COMMON_1()
 	/* We don't touch AMR here, we never go to virtual mode */
 	EXCEPTION_PROLOG_COMMON_2(PACA_EXGEN)
 	EXCEPTION_PROLOG_COMMON_3(0xe60)
 	addi	r3,r1,STACK_FRAME_OVERHEAD
-	BRANCH_LINK_TO_FAR(DOTSYM(hmi_exception_realmode)) /* Function call ABI */
+	bl	hmi_exception_realmode
 	cmpdi	cr0,r3,0
 	bne	1f
 
@@ -1742,7 +1735,8 @@ TRAMP_REAL_BEGIN(hmi_exception_early)
 	 */
 	EXCEPTION_RESTORE_REGS EXC_HV
 	EXCEPTION_PROLOG_0 PACA_EXGEN
-	b	tramp_real_hmi_exception
+	EXCEPTION_PROLOG_1 EXC_HV, PACA_EXGEN, 1, 0xe60, 0, 0, IRQS_DISABLED
+	EXCEPTION_PROLOG_2_REAL hmi_exception_common, EXC_HV, 1
 
 EXC_COMMON_BEGIN(hmi_exception_common)
 	EXCEPTION_COMMON(PACA_EXGEN, 0xe60)