[RFC PATCH v2 12/13] powerpc/kernel: Do not inconditionally save non volatile registers on system call

[Christophe Leroy]

Before : 347 cycles on null_syscall
After  : 327 cycles on null_syscall

Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>
---
 arch/powerpc/kernel/entry_32.S | 15 +++++++++++++++
 arch/powerpc/kernel/head_32.h  |  3 +--
 arch/powerpc/kernel/syscall.c  |  2 +-
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 103f5158bc44..b5113593e57f 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -315,13 +315,28 @@ stack_ovf:
 	RFI
 #endif
 
+save_nvgprs:
+	lwz	r11, _TRAP(r1)
+	andi.	r12, r11, 1
+	rlwinm	r11, r11, 0, ~1
+	beqlr
+	SAVE_NVGPRS(r1)
+	stw	r11, _TRAP(r1)
+	blr
+
 	.globl	transfer_to_syscall
 transfer_to_syscall:
+	lwz     r10, TI_FLAGS(r2)
 	mr	r9, r0
+	andi.   r10, r10, _TIF_SYSCALL_DOTRACE
 	addi	r10, r1, STACK_FRAME_OVERHEAD
+	bnel-	save_nvgprs
 	bl	system_call_exception
 ret_from_syscall:
+	lwz     r9, TI_FLAGS(r2)
 	addi    r4, r1, STACK_FRAME_OVERHEAD
+	andi.   r0, r9, _TIF_SYSCALL_DOTRACE | _TIF_SINGLESTEP | _TIF_USER_WORK_MASK
+	bnel-	save_nvgprs
 	bl	syscall_exit_prepare
 	lwz	r2, _CCR(r1)
 	lwz	r4, _NIP(r1)
diff --git a/arch/powerpc/kernel/head_32.h b/arch/powerpc/kernel/head_32.h
index c301d666a3e5..1cc9a67cb42c 100644
--- a/arch/powerpc/kernel/head_32.h
+++ b/arch/powerpc/kernel/head_32.h
@@ -174,13 +174,12 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_HPTE_TABLE)
 	stw	r2,GPR2(r11)
 	addi	r10,r10,STACK_FRAME_REGS_MARKER at l
 	stw	r9,_MSR(r11)
-	li	r2, \trapno
+	li	r2, \trapno + 1
 	stw	r10,8(r11)
 	stw	r2,_TRAP(r11)
 	SAVE_GPR(0, r11)
 	SAVE_4GPRS(3, r11)
 	SAVE_2GPRS(7, r11)
-	SAVE_NVGPRS(r11)
 	addi	r11,r1,STACK_FRAME_OVERHEAD
 	addi	r2,r12,-THREAD
 	stw	r11,PT_REGS(r12)
diff --git a/arch/powerpc/kernel/syscall.c b/arch/powerpc/kernel/syscall.c
index 630c423e089a..34fd66fd11a2 100644
--- a/arch/powerpc/kernel/syscall.c
+++ b/arch/powerpc/kernel/syscall.c
@@ -39,7 +39,7 @@ notrace long system_call_exception(long r3, long r4, long r5,
 	if (!IS_ENABLED(CONFIG_PPC_BOOK3E))
 		BUG_ON(!(regs->msr & MSR_RI));
 	BUG_ON(IS_ENABLED(CONFIG_PPC64) && !(regs->msr & MSR_PR));
-	BUG_ON(!FULL_REGS(regs));
+	BUG_ON(IS_ENABLED(CONFIG_PPC64) && !FULL_REGS(regs));
 #ifdef CONFIG_PPC64
 	BUG_ON(regs->softe != IRQS_ENABLED);
 #endif
-- 
2.25.0