[POWERPC] Clear RI bit in MSR before restoring r13 when returning to userspace

Some instruction tracing tools use the RI (recoverable interrupt) bit
in the MSR to indicate when it's safe to single-step.  Currently we
clear RI after restoring r13 when returning to userspace.  However,
if we single-step past the point where r13 is restored, we'll corrupt
r13 in the exception entry code and not restore it.  This moves the
clearing of RI to just before r13 is restored so this doesn't happen.

Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/entry_64.S

@@ -172,13 +172,18 @@ syscall_error_cont:
 	stdcx.	r0,0,r1			/* to clear the reservation */
 	andi.	r6,r8,MSR_PR
 	ld	r4,_LINK(r1)
+	/*
+	 * Clear RI before restoring r13.  If we are returning to
+	 * userspace and we take an exception after restoring r13,
+	 * we end up corrupting the userspace r13 value.
+	 */
+	li	r12,MSR_RI
+	andc	r11,r10,r12
+	mtmsrd	r11,1			/* clear MSR.RI */
 	beq-	1f
 	ACCOUNT_CPU_USER_EXIT(r11, r12)
 	ld	r13,GPR13(r1)	/* only restore r13 if returning to usermode */
 1:	ld	r2,GPR2(r1)
-	li	r12,MSR_RI
-	andc	r11,r10,r12
-	mtmsrd	r11,1			/* clear MSR.RI */
 	ld	r1,GPR1(r1)
 	mtlr	r4
 	mtcr	r5
@@ -488,42 +493,44 @@ END_FW_FTR_SECTION_IFSET(FW_FEATURE_ISERIES)
 #endif
 	stb	r5,PACASOFTIRQEN(r13)
 
+	/* extract EE bit and use it to restore paca->hard_enabled */
 	ld	r3,_MSR(r1)
+	rldicl	r4,r3,49,63		/* r0 = (r3 >> 15) & 1 */
+	stb	r4,PACAHARDIRQEN(r13)
+
+	ld	r4,_CTR(r1)
+	ld	r0,_LINK(r1)
+	mtctr	r4
+	mtlr	r0
+	ld	r4,_XER(r1)
+	mtspr	SPRN_XER,r4
+
+	REST_8GPRS(5, r1)
+
 	andi.	r0,r3,MSR_RI
 	beq-	unrecov_restore
 
-	/* extract EE bit and use it to restore paca->hard_enabled */
-	rldicl	r4,r3,49,63		/* r0 = (r3 >> 15) & 1 */
-	stb	r4,PACAHARDIRQEN(r13)
+	stdcx.	r0,0,r1		/* to clear the reservation */
 
-	andi.	r0,r3,MSR_PR
+	/*
+	 * Clear RI before restoring r13.  If we are returning to
+	 * userspace and we take an exception after restoring r13,
+	 * we end up corrupting the userspace r13 value.
+	 */
+	mfmsr	r4
+	andc	r4,r4,r0	/* r0 contains MSR_RI here */
+	mtmsrd	r4,1
 
 	/*
 	 * r13 is our per cpu area, only restore it if we are returning to
 	 * userspace
 	 */
+	andi.	r0,r3,MSR_PR
 	beq	1f
-	ACCOUNT_CPU_USER_EXIT(r3, r4)
+	ACCOUNT_CPU_USER_EXIT(r2, r4)
 	REST_GPR(13, r1)
 1:
-	ld	r3,_CTR(r1)
-	ld	r0,_LINK(r1)
-	mtctr	r3
-	mtlr	r0
-	ld	r3,_XER(r1)
-	mtspr	SPRN_XER,r3
-
-	REST_8GPRS(5, r1)
-
-	stdcx.	r0,0,r1		/* to clear the reservation */
-
-	mfmsr	r0
-	li	r2, MSR_RI
-	andc	r0,r0,r2
-	mtmsrd	r0,1
-
-	ld	r0,_MSR(r1)
-	mtspr	SPRN_SRR1,r0
+	mtspr	SPRN_SRR1,r3
 
 	ld	r2,_CCR(r1)
 	mtcrf	0xFF,r2