[RFC PATCH v3 13/15] powerpc/syscall: system call implement entry/exit logic in C for PPC32

From: Christophe Leroy
Date: Mon Apr 06 2020 - 14:17:02 EST

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That's port of PPC64 syscall entry/exit logic in C to PPC32.

Performancewise:
Before : 311 cycles on null_syscall
After : 353 cycles on null_syscall

Note: before the patch, if calling NVGPRS all the time as well,
we have 335 cycles on null_syscall

Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
---
arch/powerpc/kernel/entry_32.S | 259 ++++-----------------------------
arch/powerpc/kernel/head_32.h | 16 +-
2 files changed, 29 insertions(+), 246 deletions(-)

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index a6371fb8f761..103f5158bc44 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -315,162 +315,37 @@ stack_ovf:
RFI
#endif

-#ifdef CONFIG_TRACE_IRQFLAGS
-trace_syscall_entry_irq_off:
- /*
- * Syscall shouldn't happen while interrupts are disabled,
- * so let's do a warning here.
- */
-0: trap
- EMIT_BUG_ENTRY 0b,__FILE__,__LINE__, BUGFLAG_WARNING
- bl trace_hardirqs_on
-
- /* Now enable for real */
- LOAD_REG_IMMEDIATE(r10, MSR_KERNEL | MSR_EE)
- mtmsr r10
-
- REST_GPR(0, r1)
- REST_4GPRS(3, r1)
- REST_2GPRS(7, r1)
- b DoSyscall
-#endif /* CONFIG_TRACE_IRQFLAGS */
-
.globl transfer_to_syscall
transfer_to_syscall:
-#ifdef CONFIG_TRACE_IRQFLAGS
- andi. r12,r9,MSR_EE
- beq- trace_syscall_entry_irq_off
-#endif /* CONFIG_TRACE_IRQFLAGS */
-
-/*
- * Handle a system call.
- */
- .stabs "arch/powerpc/kernel/",N_SO,0,0,0f
- .stabs "entry_32.S",N_SO,0,0,0f
-0:
-
-_GLOBAL(DoSyscall)
- stw r3,ORIG_GPR3(r1)
- li r12,0
- stw r12,RESULT(r1)
-#ifdef CONFIG_TRACE_IRQFLAGS
- /* Make sure interrupts are enabled */
- mfmsr r11
- andi. r12,r11,MSR_EE
- /* We came in with interrupts disabled, we WARN and mark them enabled
- * for lockdep now */
-0: tweqi r12, 0
- EMIT_BUG_ENTRY 0b,__FILE__,__LINE__, BUGFLAG_WARNING
-#endif /* CONFIG_TRACE_IRQFLAGS */
- lwz r11,TI_FLAGS(r2)
- andi. r11,r11,_TIF_SYSCALL_DOTRACE
- bne- syscall_dotrace
-syscall_dotrace_cont:
- cmplwi 0,r0,NR_syscalls
- lis r10,sys_call_table@h
- ori r10,r10,sys_call_table@l
- slwi r0,r0,2
- bge- 66f
-
- barrier_nospec_asm
- /*
- * Prevent the load of the handler below (based on the user-passed
- * system call number) being speculatively executed until the test
- * against NR_syscalls and branch to .66f above has
- * committed.
- */
-
- lwzx r10,r10,r0 /* Fetch system call handler [ptr] */
- mtlr r10
- addi r9,r1,STACK_FRAME_OVERHEAD
- PPC440EP_ERR42
- blrl /* Call handler */
- .globl ret_from_syscall
+ mr r9, r0
+ addi r10, r1, STACK_FRAME_OVERHEAD
+ bl system_call_exception
ret_from_syscall:
-#ifdef CONFIG_DEBUG_RSEQ
- /* Check whether the syscall is issued inside a restartable sequence */
- stw r3,GPR3(r1)
- addi r3,r1,STACK_FRAME_OVERHEAD
- bl rseq_syscall
- lwz r3,GPR3(r1)
-#endif
- mr r6,r3
- /* disable interrupts so current_thread_info()->flags can't change */
- LOAD_REG_IMMEDIATE(r10,MSR_KERNEL) /* doesn't include MSR_EE */
- /* Note: We don't bother telling lockdep about it */
- SYNC
- mtmsr r10
- lwz r9,TI_FLAGS(r2)
- li r8,-MAX_ERRNO
- andi. r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK)
- bne- syscall_exit_work
- cmplw 0,r3,r8
- blt+ syscall_exit_cont
- lwz r11,_CCR(r1) /* Load CR */
- neg r3,r3
- oris r11,r11,0x1000 /* Set SO bit in CR */
- stw r11,_CCR(r1)
-syscall_exit_cont:
- lwz r8,_MSR(r1)
-#ifdef CONFIG_TRACE_IRQFLAGS
- /* If we are going to return from the syscall with interrupts
- * off, we trace that here. It shouldn't normally happen.
- */
- andi. r10,r8,MSR_EE
- bne+ 1f
- stw r3,GPR3(r1)
- bl trace_hardirqs_off
- lwz r3,GPR3(r1)
-1:
-#endif /* CONFIG_TRACE_IRQFLAGS */
-#if defined(CONFIG_4xx) || defined(CONFIG_BOOKE)
- /* If the process has its own DBCR0 value, load it up. The internal
- debug mode bit tells us that dbcr0 should be loaded. */
- lwz r0,THREAD+THREAD_DBCR0(r2)
- andis. r10,r0,DBCR0_IDM@h
- bnel- load_dbcr0
-#endif
-#ifdef CONFIG_44x
-BEGIN_MMU_FTR_SECTION
- lis r4,icache_44x_need_flush@ha
- lwz r5,icache_44x_need_flush@l(r4)
- cmplwi cr0,r5,0
- bne- 2f
-1:
-END_MMU_FTR_SECTION_IFCLR(MMU_FTR_TYPE_47x)
-#endif /* CONFIG_44x */
-BEGIN_FTR_SECTION
- lwarx r7,0,r1
-END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
- stwcx. r0,0,r1 /* to clear the reservation */
- ACCOUNT_CPU_USER_EXIT(r2, r5, r7)
-#ifdef CONFIG_PPC_BOOK3S_32
- kuep_unlock r5, r7
-#endif
- kuap_check r2, r4
- lwz r4,_LINK(r1)
- lwz r5,_CCR(r1)
- mtlr r4
- mtcr r5
- lwz r7,_NIP(r1)
- lwz r2,GPR2(r1)
- lwz r1,GPR1(r1)
-#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PERF_EVENTS)
- mtspr SPRN_NRI, r0
-#endif
- mtspr SPRN_SRR0,r7
- mtspr SPRN_SRR1,r8
- SYNC
- RFI
-#ifdef CONFIG_44x
-2: li r7,0
- iccci r0,r0
- stw r7,icache_44x_need_flush@l(r4)
+ addi r4, r1, STACK_FRAME_OVERHEAD
+ bl syscall_exit_prepare
+ lwz r2, _CCR(r1)
+ lwz r4, _NIP(r1)
+ lwz r5, _MSR(r1)
+ lwz r6, _LINK(r1)
+ mtspr SPRN_SRR0, r4
+ mtspr SPRN_SRR1, r5
+ mtlr r6
+ cmpwi r3, 0
+ bne 2f
+1: mtcr r2
+ REST_GPR(2, r1)
+ REST_GPR(3, r1)
+ REST_GPR(1, r1)
+ rfi
+2: lwz r3, _CTR(r1)
+ lwz r4, _XER(r1)
+ REST_NVGPRS(r1)
+ mtctr r3
+ mtspr SPRN_XER, r4
+ REST_GPR(0, r1)
+ REST_8GPRS(4, r1)
+ REST_GPR(12, r1)
b 1b
-#endif /* CONFIG_44x */
-
-66: li r3,-ENOSYS
- b ret_from_syscall

.globl ret_from_fork
ret_from_fork:
@@ -490,86 +365,6 @@ ret_from_kernel_thread:
li r3,0
b ret_from_syscall

-/* Traced system call support */
-syscall_dotrace:
- SAVE_NVGPRS(r1)
- li r0,0xc00
- stw r0,_TRAP(r1)
- addi r3,r1,STACK_FRAME_OVERHEAD
- bl do_syscall_trace_enter
- /*
- * Restore argument registers possibly just changed.
- * We use the return value of do_syscall_trace_enter
- * for call number to look up in the table (r0).
- */
- mr r0,r3
- lwz r3,GPR3(r1)
- lwz r4,GPR4(r1)
- lwz r5,GPR5(r1)
- lwz r6,GPR6(r1)
- lwz r7,GPR7(r1)
- lwz r8,GPR8(r1)
- REST_NVGPRS(r1)
-
- cmplwi r0,NR_syscalls
- /* Return code is already in r3 thanks to do_syscall_trace_enter() */
- bge- ret_from_syscall
- b syscall_dotrace_cont
-
-syscall_exit_work:
- andi. r0,r9,_TIF_RESTOREALL
- beq+ 0f
- REST_NVGPRS(r1)
- b 2f
-0: cmplw 0,r3,r8
- blt+ 1f
- andi. r0,r9,_TIF_NOERROR
- bne- 1f
- lwz r11,_CCR(r1) /* Load CR */
- neg r3,r3
- oris r11,r11,0x1000 /* Set SO bit in CR */
- stw r11,_CCR(r1)
-
-1: stw r6,RESULT(r1) /* Save result */
- stw r3,GPR3(r1) /* Update return value */
-2: andi. r0,r9,(_TIF_PERSYSCALL_MASK)
- beq 4f
-
- /* Clear per-syscall TIF flags if any are set. */
-
- li r11,_TIF_PERSYSCALL_MASK
- addi r12,r2,TI_FLAGS
-3: lwarx r8,0,r12
- andc r8,r8,r11
-#ifdef CONFIG_IBM405_ERR77
- dcbt 0,r12
-#endif
- stwcx. r8,0,r12
- bne- 3b
-
-4: /* Anything which requires enabling interrupts? */
- andi. r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP)
- beq ret_from_except
-
- /* Re-enable interrupts. There is no need to trace that with
- * lockdep as we are supposed to have IRQs on at this point
- */
- ori r10,r10,MSR_EE
- SYNC
- mtmsr r10
-
- /* Save NVGPRS if they're not saved already */
- lwz r4,_TRAP(r1)
- andi. r4,r4,1
- beq 5f
- SAVE_NVGPRS(r1)
- li r4,0xc00
- stw r4,_TRAP(r1)
-5:
- addi r3,r1,STACK_FRAME_OVERHEAD
- bl do_syscall_trace_leave
- b ret_from_except_full
-
/*
* System call was called from kernel. We get here with SRR1 in r9.
* Mark the exception as recoverable once we have retrieved SRR0,
diff --git a/arch/powerpc/kernel/head_32.h b/arch/powerpc/kernel/head_32.h
index 9abec6cd099c..c301d666a3e5 100644
--- a/arch/powerpc/kernel/head_32.h
+++ b/arch/powerpc/kernel/head_32.h
@@ -174,12 +174,13 @@ 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 + 1
+ li r2, \trapno
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)
@@ -188,9 +189,6 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_HPTE_TABLE)
internal debug mode bit to do this. */
lwz r12,THREAD_DBCR0(r12)
andis. r12,r12,DBCR0_IDM@h
-#endif
- ACCOUNT_CPU_USER_ENTRY(r2, r11, r12)
-#if defined(CONFIG_40x)
beq+ 3f
/* From user and task is ptraced - load up global dbcr0 */
li r12,-1 /* clear all pending debug events */
@@ -209,17 +207,7 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_HPTE_TABLE)
tovirt_novmstack r2, r2 /* set r2 to current */
lis r11, transfer_to_syscall@h
ori r11, r11, transfer_to_syscall@l
-#ifdef CONFIG_TRACE_IRQFLAGS
- /*
- * If MSR is changing we need to keep interrupts disabled at this point
- * otherwise we might risk taking an interrupt before we tell lockdep
- * they are enabled.
- */
LOAD_REG_IMMEDIATE(r10, MSR_KERNEL)
- rlwimi r10, r9, 0, MSR_EE
-#else
- LOAD_REG_IMMEDIATE(r10, MSR_KERNEL | MSR_EE)
-#endif
#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PERF_EVENTS)
mtspr SPRN_NRI, r0
#endif
--
2.25.0

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Previous message: Christophe Leroy: "[RFC PATCH v3 15/15] powerpc/kernel: Do not inconditionally save non volatile registers on system call"
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