powerpc/32: Always save non volatile registers on exception entry

In preparation of handling exception entry and exit in C,
in order to simplify the handling, always save non volatile registers
when entering an exception.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/3ce8ced87a4f1467fa36fcc50763d53b45e466c1.1615552867.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/ptrace.h

@@ -209,16 +209,14 @@ static inline void regs_set_return_value(struct pt_regs *regs, unsigned long rc)
  */
 #define TRAP_FLAGS_MASK		0x1F
 #define TRAP(regs)		((regs)->trap & ~TRAP_FLAGS_MASK)
-#define FULL_REGS(regs)		(((regs)->trap & 1) == 0)
-#define SET_FULL_REGS(regs)	((regs)->trap &= ~1)
+#define FULL_REGS(regs)		true
+#define SET_FULL_REGS(regs)	do { } while (0)
 #define IS_CRITICAL_EXC(regs)	(((regs)->trap & 2) != 0)
 #define IS_MCHECK_EXC(regs)	(((regs)->trap & 4) != 0)
 #define IS_DEBUG_EXC(regs)	(((regs)->trap & 8) != 0)
 #define NV_REG_POISON		0xdeadbeef
 #define CHECK_FULL_REGS(regs)						      \
 do {									      \
-	if ((regs)->trap & 1)						      \
-		printk(KERN_CRIT "%s: partial register set\n", __func__); \
 } while (0)
 #endif /* __powerpc64__ */
 

arch/powerpc/kernel/entry_32.S

@@ -81,12 +81,12 @@ _ASM_NOKPROBE_SYMBOL(crit_transfer_to_handler)
  */
 	.globl	transfer_to_handler_full
 transfer_to_handler_full:
-	SAVE_NVGPRS(r11)
 _ASM_NOKPROBE_SYMBOL(transfer_to_handler_full)
 	/* fall through */
 
 	.globl	transfer_to_handler
 transfer_to_handler:
+	SAVE_NVGPRS(r11)
 	stw	r2,GPR2(r11)
 	stw	r12,_NIP(r11)
 	stw	r9,_MSR(r11)
@@ -234,10 +234,6 @@ handle_page_fault:
 	bl	do_page_fault
 	cmpwi	r3,0
 	beq+	ret_from_except
-	SAVE_NVGPRS(r1)
-	lwz	r0,_TRAP(r1)
-	clrrwi	r0,r0,1
-	stw	r0,_TRAP(r1)
 	mr	r4,r3		/* err arg for bad_page_fault */
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	bl	__bad_page_fault
@@ -810,13 +806,6 @@ recheck:
 do_user_signal:			/* r10 contains MSR_KERNEL here */
 	ori	r10,r10,MSR_EE
 	mtmsr	r10		/* hard-enable interrupts */
-	/* save r13-r31 in the exception frame, if not already done */
-	lwz	r3,_TRAP(r1)
-	andi.	r0,r3,1
-	beq	2f
-	SAVE_NVGPRS(r1)
-	rlwinm	r3,r3,0,0,30
-	stw	r3,_TRAP(r1)
 2:	addi	r3,r1,STACK_FRAME_OVERHEAD
 	mr	r4,r9
 	bl	do_notify_resume

arch/powerpc/kernel/head_32.h

@@ -198,7 +198,7 @@ _ASM_NOKPROBE_SYMBOL(\name\()_virt)
 			  ret_from_except_full)
 
 #define EXC_XFER_LITE(n, hdlr)		\
-	EXC_XFER_TEMPLATE(hdlr, n+1, MSR_KERNEL, transfer_to_handler, \
+	EXC_XFER_TEMPLATE(hdlr, n, MSR_KERNEL, transfer_to_handler, \
 			  ret_from_except)
 
 .macro vmap_stack_overflow_exception
@@ -215,7 +215,6 @@ _ASM_NOKPROBE_SYMBOL(\name\()_virt)
 	lwz	r1, emergency_ctx@l(r1)
 	addi	r1, r1, THREAD_SIZE - INT_FRAME_SIZE
 	EXCEPTION_PROLOG_2 vmap_stack_overflow
-	SAVE_NVGPRS(r11)
 	addi	r3, r1, STACK_FRAME_OVERHEAD
 	EXC_XFER_STD(0, stack_overflow_exception)
 .endm

arch/powerpc/kernel/head_booke.h

@@ -331,7 +331,7 @@ ALT_FTR_SECTION_END_IFSET(CPU_FTR_EMB_HV)
 			  ret_from_except_full)
 
 #define EXC_XFER_LITE(n, hdlr)		\
-	EXC_XFER_TEMPLATE(hdlr, n+1, MSR_KERNEL, transfer_to_handler, \
+	EXC_XFER_TEMPLATE(hdlr, n, MSR_KERNEL, transfer_to_handler, \
 			  ret_from_except)
 
 /* Check for a single step debug exception while in an exception