powerpc/32: Always save non volatile GPRs at syscall entry

In preparation for porting syscall entry/exit to C, inconditionally
save non volatile general purpose registers.

Commit 965dd3ad ("powerpc/64/syscall: Remove non-volatile GPR save
optimisation") provides detailed explanation.

This increases the number of cycles by 24 cycles on 8xx with
null_syscall benchmark (280 => 304 cycles)
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/21c08162b83655195fe9ead78ff2cfd28508d023.1612796617.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/entry_32.S

@@ -351,6 +351,7 @@ trace_syscall_entry_irq_off:
 
 	.globl	transfer_to_syscall
 transfer_to_syscall:
+	SAVE_NVGPRS(r1)
 #ifdef CONFIG_PPC_BOOK3S_32
 	kuep_lock r11, r12
 #endif
@@ -614,51 +615,6 @@ ret_from_kernel_syscall:
 #endif
 _ASM_NOKPROBE_SYMBOL(ret_from_kernel_syscall)
 
-/*
- * The fork/clone functions need to copy the full register set into
- * the child process. Therefore we need to save all the nonvolatile
- * registers (r13 - r31) before calling the C code.
- */
-	.globl	ppc_fork
-ppc_fork:
-	SAVE_NVGPRS(r1)
-	lwz	r0,_TRAP(r1)
-	rlwinm	r0,r0,0,0,30		/* clear LSB to indicate full */
-	stw	r0,_TRAP(r1)		/* register set saved */
-	b	sys_fork
-
-	.globl	ppc_vfork
-ppc_vfork:
-	SAVE_NVGPRS(r1)
-	lwz	r0,_TRAP(r1)
-	rlwinm	r0,r0,0,0,30		/* clear LSB to indicate full */
-	stw	r0,_TRAP(r1)		/* register set saved */
-	b	sys_vfork
-
-	.globl	ppc_clone
-ppc_clone:
-	SAVE_NVGPRS(r1)
-	lwz	r0,_TRAP(r1)
-	rlwinm	r0,r0,0,0,30		/* clear LSB to indicate full */
-	stw	r0,_TRAP(r1)		/* register set saved */
-	b	sys_clone
-
-	.globl	ppc_clone3
-ppc_clone3:
-	SAVE_NVGPRS(r1)
-	lwz	r0,_TRAP(r1)
-	rlwinm	r0,r0,0,0,30		/* clear LSB to indicate full */
-	stw	r0,_TRAP(r1)		/* register set saved */
-	b	sys_clone3
-
-	.globl	ppc_swapcontext
-ppc_swapcontext:
-	SAVE_NVGPRS(r1)
-	lwz	r0,_TRAP(r1)
-	rlwinm	r0,r0,0,0,30		/* clear LSB to indicate full */
-	stw	r0,_TRAP(r1)		/* register set saved */
-	b	sys_swapcontext
-
 /*
  * Top-level page fault handling.
  * This is in assembler because if do_page_fault tells us that

arch/powerpc/kernel/head_32.h

@@ -148,7 +148,7 @@
 	stw	r2,GPR2(r11)
 	addi	r10,r10,STACK_FRAME_REGS_MARKER@l
 	stw	r9,_MSR(r11)
-	li	r2, \trapno + 1
+	li	r2, \trapno
 	stw	r10,8(r11)
 	stw	r2,_TRAP(r11)
 	SAVE_GPR(0, r11)

arch/powerpc/kernel/head_booke.h

@@ -124,7 +124,7 @@ ALT_FTR_SECTION_END_IFSET(CPU_FTR_EMB_HV)
 	stw	r2,GPR2(r11)
 	addi	r12, r12, STACK_FRAME_REGS_MARKER@l
 	stw	r9,_MSR(r11)
-	li	r2, \trapno + 1
+	li	r2, \trapno
 	stw	r12, 8(r11)
 	stw	r2,_TRAP(r11)
 	SAVE_GPR(0, r11)

arch/powerpc/kernel/syscalls/syscall.tbl

@@ -9,9 +9,7 @@
 #
 0	nospu	restart_syscall			sys_restart_syscall
 1	nospu	exit				sys_exit
-2	32	fork				ppc_fork			sys_fork
-2	64	fork				sys_fork
-2	spu	fork				sys_ni_syscall
+2	nospu	fork				sys_fork
 3	common	read				sys_read
 4	common	write				sys_write
 5	common	open				sys_open			compat_sys_open
@@ -160,9 +158,7 @@
 119	32	sigreturn			sys_sigreturn			compat_sys_sigreturn
 119	64	sigreturn			sys_ni_syscall
 119	spu	sigreturn			sys_ni_syscall
-120	32	clone				ppc_clone			sys_clone
-120	64	clone				sys_clone
-120	spu	clone				sys_ni_syscall
+120	nospu	clone				sys_clone
 121	common	setdomainname			sys_setdomainname
 122	common	uname				sys_newuname
 123	common	modify_ldt			sys_ni_syscall
@@ -244,9 +240,7 @@
 186	spu	sendfile			sys_sendfile64
 187	common	getpmsg				sys_ni_syscall
 188	common 	putpmsg				sys_ni_syscall
-189	32	vfork				ppc_vfork			sys_vfork
-189	64	vfork				sys_vfork
-189	spu	vfork				sys_ni_syscall
+189	nospu	vfork				sys_vfork
 190	common	ugetrlimit			sys_getrlimit			compat_sys_getrlimit
 191	common	readahead			sys_readahead			compat_sys_readahead
 192	32	mmap2				sys_mmap2			compat_sys_mmap2
@@ -322,9 +316,7 @@
 248	32	clock_nanosleep			sys_clock_nanosleep_time32
 248	64	clock_nanosleep			sys_clock_nanosleep
 248	spu	clock_nanosleep			sys_clock_nanosleep
-249	32	swapcontext			ppc_swapcontext			compat_sys_swapcontext
-249	64	swapcontext			sys_swapcontext
-249	spu	swapcontext			sys_ni_syscall
+249	nospu	swapcontext			sys_swapcontext			compat_sys_swapcontext
 250	common	tgkill				sys_tgkill
 251	32	utimes				sys_utimes_time32
 251	64	utimes				sys_utimes
@@ -522,9 +514,7 @@
 432	common	fsmount				sys_fsmount
 433	common	fspick				sys_fspick
 434	common	pidfd_open			sys_pidfd_open
-435	32	clone3				ppc_clone3			sys_clone3
-435	64	clone3				sys_clone3
-435	spu	clone3				sys_ni_syscall
+435	nospu	clone3				sys_clone3
 436	common	close_range			sys_close_range
 437	common	openat2				sys_openat2
 438	common	pidfd_getfd			sys_pidfd_getfd