powerpc/64s/exception: simplify machine check early path

machine_check_handle_early_common can reach machine_check_handle_early
directly now that it runs at the relocated address, so just branch
directly.

The rfi sequence is required to enable MSR[ME] but that step is moved
into a helper function, making the code easier to follow.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190802105709.27696-14-npiggin@gmail.com

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

@@ -1006,16 +1006,13 @@ EXC_COMMON_BEGIN(machine_check_early_common)
 	std	r3,_DAR(r1)
 	std	r4,_DSISR(r1)
 
-	mfmsr	r11			/* get MSR value */
 BEGIN_FTR_SECTION
-	ori	r11,r11,MSR_ME		/* turn on ME bit */
+	bl	enable_machine_check
 END_FTR_SECTION_IFSET(CPU_FTR_HVMODE)
-	ori	r11,r11,MSR_RI		/* turn on RI bit */
-	LOAD_HANDLER(r12, machine_check_handle_early)
-1:	mtspr	SPRN_SRR0,r12
-	mtspr	SPRN_SRR1,r11
-	RFI_TO_KERNEL
-	b	.	/* prevent speculative execution */
+	li	r10,MSR_RI
+	mtmsrd	r10,1
+	b	machine_check_handle_early
+
 2:
 	/* Stack overflow. Stay on emergency stack and panic.
 	 * Keep the ME bit off while panic-ing, so that if we hit
@@ -1026,7 +1023,9 @@ END_FTR_SECTION_IFSET(CPU_FTR_HVMODE)
 	LOAD_HANDLER(r12, unrecover_mce)
 	li	r10,MSR_ME
 	andc	r11,r11,r10		/* Turn off MSR_ME */
-	b	1b
+	mtspr	SPRN_SRR0,r12
+	mtspr	SPRN_SRR1,r11
+	RFI_TO_KERNEL
 	b	.	/* prevent speculative execution */
 
 EXC_COMMON_BEGIN(machine_check_common)
@@ -2269,6 +2268,20 @@ CLOSE_FIXED_SECTION(virt_trampolines);
 
 USE_TEXT_SECTION()
 
+/* MSR[RI] should be clear because this uses SRR[01] */
+enable_machine_check:
+	mflr	r0
+	bcl	20,31,$+4
+0:	mflr	r3
+	addi	r3,r3,(1f - 0b)
+	mtspr	SPRN_SRR0,r3
+	mfmsr	r3
+	ori	r3,r3,MSR_ME
+	mtspr	SPRN_SRR1,r3
+	RFI_TO_KERNEL
+1:	mtlr	r0
+	blr
+
 /*
  * Hash table stuff
  */