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Subject[RFC PATCH v2 12/13] powerpc/kernel: Do not inconditionally save non volatile registers on system call
Date
Before : 347 cycles on null_syscall
After : 327 cycles on null_syscall

Signed-off-by: Christophe Leroy <christophe.leroy@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@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
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