powerpc/40x: Save SRR0/SRR1 and r10/r11 earlier in critical exception

In order to be able to switch MMU on in exception prolog, save
SRR0 and SRR1 earlier.

Also save r10 and r11 into stack earlier to better match with the
normal exception prolog.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/79a93f253d72dc97ac968c9c62b5066960b688ed.1615552866.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/entry_32.S

@@ -107,15 +107,6 @@ _ASM_NOKPROBE_SYMBOL(crit_transfer_to_handler)
 #ifdef CONFIG_40x
 	.globl	crit_transfer_to_handler
 crit_transfer_to_handler:
-	lwz	r0,crit_r10@l(0)
-	stw	r0,GPR10(r11)
-	lwz	r0,crit_r11@l(0)
-	stw	r0,GPR11(r11)
-	mfspr	r0,SPRN_SRR0
-	stw	r0,crit_srr0@l(0)
-	mfspr	r0,SPRN_SRR1
-	stw	r0,crit_srr1@l(0)
-
 	/* set the stack limit to the current stack */
 	mfspr	r8,SPRN_SPRG_THREAD
 	lwz	r0,KSP_LIMIT(r8)

arch/powerpc/kernel/head_40x.S

@@ -103,6 +103,10 @@ _ENTRY(saved_ksp_limit)
 .macro CRITICAL_EXCEPTION_PROLOG
 	stw	r10,crit_r10@l(0)	/* save two registers to work with */
 	stw	r11,crit_r11@l(0)
+	mfspr	r10,SPRN_SRR0
+	mfspr	r11,SPRN_SRR1
+	stw	r10,crit_srr0@l(0)
+	stw	r11,crit_srr1@l(0)
 	mfcr	r10			/* save CR in r10 for now	   */
 	mfspr	r11,SPRN_SRR3		/* check whether user or kernel    */
 	andi.	r11,r11,MSR_PR
@@ -120,6 +124,10 @@ _ENTRY(saved_ksp_limit)
 	stw	r9,GPR9(r11)
 	mflr	r10
 	stw	r10,_LINK(r11)
+	lwz	r10,crit_r10@l(0)
+	lwz	r12,crit_r11@l(0)
+	stw	r10,GPR10(r11)
+	stw	r12,GPR11(r11)
 	mfspr	r12,SPRN_DEAR		/* save DEAR and ESR in the frame  */
 	stw	r12,_DEAR(r11)		/* since they may have had stuff   */
 	mfspr	r9,SPRN_ESR		/* in them at the point where the  */