powerpc/32: Save remaining registers in exception prolog

Save non volatile registers, XER, CTR, MSR and NIP in exception prolog.

Also assign proper value to r2 and r3 there.

For now, recalculate thread pointer in prepare_transfer_to_handler.
It will disappear once KUAP is ported to C.

And remove the comment which is now completely wrong.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/56f0cde9dd0362edf2ddba4d887552013eee7329.1615552867.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/entry_32.S

@@ -48,29 +48,11 @@
  */
 	.align	12
 
-/*
- * This code finishes saving the registers to the exception frame
- * and jumps to the appropriate handler for the exception, turning
- * on address translation.
- * Note that we rely on the caller having set cr0.eq iff the exception
- * occurred in kernel mode (i.e. MSR:PR = 0).
- */
 	.globl	prepare_transfer_to_handler
 prepare_transfer_to_handler:
-	SAVE_NVGPRS(r11)
-	addi	r3,r1,STACK_FRAME_OVERHEAD
-	stw	r2,GPR2(r11)
-	stw	r12,_NIP(r11)
-	stw	r9,_MSR(r11)
-	andi.	r2,r9,MSR_PR
-	mfctr	r12
-	mfspr	r2,SPRN_XER
-	stw	r12,_CTR(r11)
-	stw	r2,_XER(r11)
-	mfspr	r12,SPRN_SPRG_THREAD
-	tovirt(r12, r12)
+	andi.	r12,r9,MSR_PR
+	addi	r12,r2,THREAD
 	beq	2f
-	addi	r2, r12, -THREAD
 #ifdef CONFIG_PPC_BOOK3S_32
 	kuep_lock r11, r12
 #endif
@@ -78,8 +60,7 @@ prepare_transfer_to_handler:
 
 	/* if from kernel, check interrupted DOZE/NAP mode */
 2:
-	kuap_save_and_lock r11, r12, r9, r2, r6
-	addi	r2, r12, -THREAD
+	kuap_save_and_lock r11, r12, r9, r5, r6
 #if defined(CONFIG_PPC_BOOK3S_32) || defined(CONFIG_E500)
 	lwz	r12,TI_LOCAL_FLAGS(r2)
 	mtcrf	0x01,r12
@@ -293,7 +274,7 @@ fast_exception_return:
 
 2:	REST_4GPRS(3, r11)
 	lwz	r10,_CCR(r11)
-	REST_GPR(1, r11)
+	REST_2GPRS(1, r11)
 	mtcr	r10
 	lwz	r10,_LINK(r11)
 	mtlr	r10

arch/powerpc/kernel/head_32.h

@@ -117,6 +117,18 @@ _ASM_NOKPROBE_SYMBOL(\name\()_virt)
 	stw	r10,_TRAP(r1)
 	SAVE_4GPRS(3, r1)
 	SAVE_2GPRS(7, r1)
+	SAVE_NVGPRS(r1)
+	stw	r2,GPR2(r1)
+	stw	r12,_NIP(r1)
+	stw	r9,_MSR(r1)
+	mfctr	r10
+	mfspr	r2,SPRN_SPRG_THREAD
+	stw	r10,_CTR(r1)
+	tovirt(r2, r2)
+	mfspr	r10,SPRN_XER
+	addi	r2, r2, -THREAD
+	stw	r10,_XER(r1)
+	addi	r3,r1,STACK_FRAME_OVERHEAD
 .endm
 
 .macro prepare_transfer_to_handler

arch/powerpc/kernel/head_booke.h

@@ -89,6 +89,18 @@ END_BTB_FLUSH_SECTION
 	stw	r10,_TRAP(r1)
 	SAVE_4GPRS(3, r1)
 	SAVE_2GPRS(7, r1)
+	SAVE_NVGPRS(r1)
+	stw	r2,GPR2(r1)
+	stw	r12,_NIP(r1)
+	stw	r9,_MSR(r1)
+	mfctr	r10
+	mfspr	r2,SPRN_SPRG_THREAD
+	stw	r10,_CTR(r1)
+	tovirt(r2, r2)
+	mfspr	r10,SPRN_XER
+	addi	r2, r2, -THREAD
+	stw	r10,_XER(r1)
+	addi	r3,r1,STACK_FRAME_OVERHEAD
 .endm
 
 .macro prepare_transfer_to_handler