powerpc/syscall: implement system call entry/exit logic in C for PPC32

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

Performancewise on 8xx:
Before : 304 cycles on null_syscall
After  : 348 cycles on null_syscall

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/a93b08e1275e9d1f0b1c39043d1b827586b2b401.1612796617.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/entry_32.S

@@ -329,117 +329,23 @@ stack_ovf:
 _ASM_NOKPROBE_SYMBOL(stack_ovf)
 #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:
 	SAVE_NVGPRS(r1)
 #ifdef CONFIG_PPC_BOOK3S_32
 	kuep_lock r11, r12
 #endif
-#ifdef CONFIG_TRACE_IRQFLAGS
-	andi.	r12,r9,MSR_EE
-	beq-	trace_syscall_entry_irq_off
-#endif /* CONFIG_TRACE_IRQFLAGS */
 
-/*
+	/* Calling convention has r9 = orig r0, r10 = regs */
- * Handle a system call.
+	addi	r10,r1,STACK_FRAME_OVERHEAD
- */
+	mr	r9,r0
-	.stabs	"arch/powerpc/kernel/",N_SO,0,0,0f
+	stw	r10,THREAD+PT_REGS(r2)
-	.stabs	"entry_32.S",N_SO,0,0,0f
+	bl	system_call_exception
-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
 ret_from_syscall:
-#ifdef CONFIG_DEBUG_RSEQ
+	addi    r4,r1,STACK_FRAME_OVERHEAD
-	/* Check whether the syscall is issued inside a restartable sequence */
+	li	r5,0
-	stw	r3,GPR3(r1)
+	bl	syscall_exit_prepare
-	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 */
-	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. */
@@ -453,12 +359,6 @@ syscall_exit_cont:
 	cmplwi	cr0,r5,0
 	bne-	2f
 #endif /* CONFIG_PPC_47x */
-1:
-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
@@ -466,21 +366,36 @@ END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
 	lwz	r4,_LINK(r1)
 	lwz	r5,_CCR(r1)
 	mtlr	r4
-	mtcr	r5
 	lwz	r7,_NIP(r1)
-	lwz	r2,GPR2(r1)
+	lwz	r8,_MSR(r1)
-	lwz	r1,GPR1(r1)
+	cmpwi	r3,0
+	lwz	r3,GPR3(r1)
 syscall_exit_finish:
-#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PERF_EVENTS)
-	mtspr	SPRN_NRI, r0
-#endif
 	mtspr	SPRN_SRR0,r7
 	mtspr	SPRN_SRR1,r8
+
+	bne	3f
+	mtcr	r5
+
+1:	lwz	r2,GPR2(r1)
+	lwz	r1,GPR1(r1)
 	rfi
 #ifdef CONFIG_40x
 	b .	/* Prevent prefetch past rfi */
 #endif
-_ASM_NOKPROBE_SYMBOL(syscall_exit_finish)
+
+3:	mtcr	r5
+	lwz	r4,_CTR(r1)
+	lwz	r5,_XER(r1)
+	REST_NVGPRS(r1)
+	mtctr	r4
+	mtxer	r5
+	lwz	r0,GPR0(r1)
+	lwz	r3,GPR3(r1)
+	REST_8GPRS(4,r1)
+	lwz	r12,GPR12(r1)
+	b	1b
+
 #ifdef CONFIG_44x
 2:	li	r7,0
 	iccci	r0,r0
@@ -488,9 +403,6 @@ _ASM_NOKPROBE_SYMBOL(syscall_exit_finish)
 	b	1b
 #endif  /* CONFIG_44x */
 
-66:	li	r3,-ENOSYS
-	b	ret_from_syscall
-
 	.globl	ret_from_fork
 ret_from_fork:
 	REST_NVGPRS(r1)
@@ -509,82 +421,6 @@ 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
-	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
-	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,

arch/powerpc/kernel/head_32.h

@@ -154,17 +154,12 @@
 	SAVE_GPR(0, r11)
 	SAVE_4GPRS(3, r11)
 	SAVE_2GPRS(7, r11)
-	addi	r11,r1,STACK_FRAME_OVERHEAD
 	addi	r2,r12,-THREAD
-	stw	r11,PT_REGS(r12)
 #if defined(CONFIG_40x)
 	/* Check to see if the dbcr0 register is set up to debug.  Use the
 	   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 */
@@ -176,21 +171,8 @@
 	lwz	r12,4(r11)
 	addi	r12,r12,-1
 	stw	r12,4(r11)
-#endif
-
 3:
-#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
-	mtmsr	r10
 	b	transfer_to_syscall		/* jump to handler */
 99:	b	ret_from_kernel_syscall
 .endm

arch/powerpc/kernel/head_booke.h

@@ -131,14 +131,11 @@ ALT_FTR_SECTION_END_IFSET(CPU_FTR_EMB_HV)
 	SAVE_4GPRS(3, r11)
 	SAVE_2GPRS(7, r11)
 
-	addi	r11,r1,STACK_FRAME_OVERHEAD
 	addi	r2,r10,-THREAD
-	stw	r11,PT_REGS(r10)
 	/* Check to see if the dbcr0 register is set up to debug.  Use the
 	   internal debug mode bit to do this. */
 	lwz	r12,THREAD_DBCR0(r10)
 	andis.	r12,r12,DBCR0_IDM@h
-	ACCOUNT_CPU_USER_ENTRY(r2, r11, r12)
 	beq+	3f
 	/* From user and task is ptraced - load up global dbcr0 */
 	li	r12,-1			/* clear all pending debug events */
@@ -157,20 +154,6 @@ ALT_FTR_SECTION_END_IFSET(CPU_FTR_EMB_HV)
 	stw	r12,4(r11)
 
 3:
-#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.
-	 */
-	lis	r10, MSR_KERNEL@h
-	ori	r10, r10, MSR_KERNEL@l
-	rlwimi	r10, r9, 0, MSR_EE
-#else
-	lis	r10, (MSR_KERNEL | MSR_EE)@h
-	ori	r10, r10, (MSR_KERNEL | MSR_EE)@l
-#endif
-	mtmsr	r10
 	b	transfer_to_syscall	/* jump to handler */
 99:	b	ret_from_kernel_syscall
 .endm