powerpc/32: On syscall entry, enable instruction translation at the same time as data

On 40x and 8xx, kernel text is pinned.
On book3s/32, kernel text is mapped by BATs.

Enable instruction translation at the same time as data translation, it
makes things simpler.

MSR_RI can also be set at the same time because srr0/srr1 are already
saved and r1 is set properly.

On booke, translation is always on, so at the end all PPC32
have translation on early.

This reduces null_syscall benchmark by 13 cycles on 8xx
(296 ==> 283 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/3fe8891c814103a3549efc1d4e7ffc828bba5993.1612796617.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/head_32.h

@@ -125,9 +125,13 @@
 	lwz	r1,TASK_STACK-THREAD(r12)
 	beq-	99f
 	addi	r1, r1, THREAD_SIZE - INT_FRAME_SIZE
-	LOAD_REG_IMMEDIATE(r10, MSR_KERNEL & ~(MSR_IR | MSR_RI)) /* can take DTLB miss */
-	mtmsr	r10
-	isync
+	LOAD_REG_IMMEDIATE(r10, MSR_KERNEL)		/* can take exceptions */
+	mtspr	SPRN_SRR1, r10
+	lis	r10, 1f@h
+	ori	r10, r10, 1f@l
+	mtspr	SPRN_SRR0, r10
+	rfi
+1:
 	tovirt(r12, r12)
 	stw	r11,GPR1(r1)
 	stw	r11,0(r1)
@@ -141,9 +145,6 @@
 	stw	r10,_CCR(r11)		/* save registers */
 #ifdef CONFIG_40x
 	rlwinm	r9,r9,0,14,12		/* clear MSR_WE (necessary?) */
-#else
-	LOAD_REG_IMMEDIATE(r10, MSR_KERNEL & ~MSR_IR) /* can take exceptions */
-	mtmsr	r10			/* (except for mach check in rtas) */
 #endif
 	lis	r10,STACK_FRAME_REGS_MARKER@ha /* exception frame marker */
 	stw	r2,GPR2(r11)
@@ -180,8 +181,6 @@
 #endif
 
 3:
-	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
@@ -193,15 +192,8 @@
 #else
 	LOAD_REG_IMMEDIATE(r10, MSR_KERNEL | MSR_EE)
 #endif
-#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PERF_EVENTS)
-	mtspr	SPRN_NRI, r0
-#endif
-	mtspr	SPRN_SRR1,r10
-	mtspr	SPRN_SRR0,r11
-	rfi				/* jump to handler, enable MMU */
-#ifdef CONFIG_40x
-	b .	/* Prevent prefetch past rfi */
-#endif
+	mtmsr	r10
+	b	transfer_to_syscall		/* jump to handler */
 99:	b	ret_from_kernel_syscall
 .endm
 

arch/powerpc/kernel/head_booke.h

@@ -157,8 +157,6 @@ ALT_FTR_SECTION_END_IFSET(CPU_FTR_EMB_HV)
 	stw	r12,4(r11)
 
 3:
-	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
@@ -172,9 +170,8 @@ ALT_FTR_SECTION_END_IFSET(CPU_FTR_EMB_HV)
 	lis	r10, (MSR_KERNEL | MSR_EE)@h
 	ori	r10, r10, (MSR_KERNEL | MSR_EE)@l
 #endif
-	mtspr	SPRN_SRR1,r10
-	mtspr	SPRN_SRR0,r11
-	rfi				/* jump to handler, enable MMU */
+	mtmsr	r10
+	b	transfer_to_syscall	/* jump to handler */
 99:	b	ret_from_kernel_syscall
 .endm