powerpc/64s: move stack SLB pinning out of line from _switch

The large hunk of SLB pinning in _switch asm code makes it more
difficult to see everything else that's going on. It is a less important
path now, so icache and fetch footprint overhead can be avoided.

Move context switch stack SLB pinning out of line.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230606132447.315714-2-npiggin@gmail.com

arch/powerpc/kernel/entry_64.S

@@ -105,6 +105,64 @@ flush_branch_caches:
 	.endr
 
 	blr
+
+#ifdef CONFIG_PPC_64S_HASH_MMU
+.balign 32
+/*
+ * New stack pointer in r8, old stack pointer in r1, must not clobber r3
+ */
+pin_stack_slb:
+BEGIN_FTR_SECTION
+	clrrdi	r6,r8,28	/* get its ESID */
+	clrrdi	r9,r1,28	/* get current sp ESID */
+FTR_SECTION_ELSE
+	clrrdi	r6,r8,40	/* get its 1T ESID */
+	clrrdi	r9,r1,40	/* get current sp 1T ESID */
+ALT_MMU_FTR_SECTION_END_IFCLR(MMU_FTR_1T_SEGMENT)
+	clrldi.	r0,r6,2		/* is new ESID c00000000? */
+	cmpd	cr1,r6,r9	/* or is new ESID the same as current ESID? */
+	cror	eq,4*cr1+eq,eq
+	beq	2f		/* if yes, don't slbie it */
+
+	/* Bolt in the new stack SLB entry */
+	ld	r7,KSP_VSID(r4)	/* Get new stack's VSID */
+	oris	r0,r6,(SLB_ESID_V)@h
+	ori	r0,r0,(SLB_NUM_BOLTED-1)@l
+BEGIN_FTR_SECTION
+	li	r9,MMU_SEGSIZE_1T	/* insert B field */
+	oris	r6,r6,(MMU_SEGSIZE_1T << SLBIE_SSIZE_SHIFT)@h
+	rldimi	r7,r9,SLB_VSID_SSIZE_SHIFT,0
+END_MMU_FTR_SECTION_IFSET(MMU_FTR_1T_SEGMENT)
+
+	/* Update the last bolted SLB.  No write barriers are needed
+	 * here, provided we only update the current CPU's SLB shadow
+	 * buffer.
+	 */
+	ld	r9,PACA_SLBSHADOWPTR(r13)
+	li	r12,0
+	std	r12,SLBSHADOW_STACKESID(r9)	/* Clear ESID */
+	li	r12,SLBSHADOW_STACKVSID
+	STDX_BE	r7,r12,r9			/* Save VSID */
+	li	r12,SLBSHADOW_STACKESID
+	STDX_BE	r0,r12,r9			/* Save ESID */
+
+	/* No need to check for MMU_FTR_NO_SLBIE_B here, since when
+	 * we have 1TB segments, the only CPUs known to have the errata
+	 * only support less than 1TB of system memory and we'll never
+	 * actually hit this code path.
+	 */
+
+	isync
+	slbie	r6
+BEGIN_FTR_SECTION
+	slbie	r6		/* Workaround POWER5 < DD2.1 issue */
+END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)
+	slbmte	r7,r0
+	isync
+2:	blr
+	.size pin_stack_slb,.-pin_stack_slb
+#endif /* CONFIG_PPC_64S_HASH_MMU */
+
 #else
 #define FLUSH_COUNT_CACHE
 #endif /* CONFIG_PPC_BOOK3S_64 */
@@ -182,59 +240,12 @@ _GLOBAL(_switch)
 #endif
 
 	ld	r8,KSP(r4)	/* new stack pointer */
+
 #ifdef CONFIG_PPC_64S_HASH_MMU
 BEGIN_MMU_FTR_SECTION
-	b	2f
-END_MMU_FTR_SECTION_IFSET(MMU_FTR_TYPE_RADIX)
-BEGIN_FTR_SECTION
-	clrrdi	r6,r8,28	/* get its ESID */
-	clrrdi	r9,r1,28	/* get current sp ESID */
-FTR_SECTION_ELSE
-	clrrdi	r6,r8,40	/* get its 1T ESID */
-	clrrdi	r9,r1,40	/* get current sp 1T ESID */
-ALT_MMU_FTR_SECTION_END_IFCLR(MMU_FTR_1T_SEGMENT)
-	clrldi.	r0,r6,2		/* is new ESID c00000000? */
-	cmpd	cr1,r6,r9	/* or is new ESID the same as current ESID? */
-	cror	eq,4*cr1+eq,eq
-	beq	2f		/* if yes, don't slbie it */
-
-	/* Bolt in the new stack SLB entry */
-	ld	r7,KSP_VSID(r4)	/* Get new stack's VSID */
-	oris	r0,r6,(SLB_ESID_V)@h
-	ori	r0,r0,(SLB_NUM_BOLTED-1)@l
-BEGIN_FTR_SECTION
-	li	r9,MMU_SEGSIZE_1T	/* insert B field */
-	oris	r6,r6,(MMU_SEGSIZE_1T << SLBIE_SSIZE_SHIFT)@h
-	rldimi	r7,r9,SLB_VSID_SSIZE_SHIFT,0
-END_MMU_FTR_SECTION_IFSET(MMU_FTR_1T_SEGMENT)
-
-	/* Update the last bolted SLB.  No write barriers are needed
-	 * here, provided we only update the current CPU's SLB shadow
-	 * buffer.
-	 */
-	ld	r9,PACA_SLBSHADOWPTR(r13)
-	li	r12,0
-	std	r12,SLBSHADOW_STACKESID(r9)	/* Clear ESID */
-	li	r12,SLBSHADOW_STACKVSID
-	STDX_BE	r7,r12,r9			/* Save VSID */
-	li	r12,SLBSHADOW_STACKESID
-	STDX_BE	r0,r12,r9			/* Save ESID */
-
-	/* No need to check for MMU_FTR_NO_SLBIE_B here, since when
-	 * we have 1TB segments, the only CPUs known to have the errata
-	 * only support less than 1TB of system memory and we'll never
-	 * actually hit this code path.
-	 */
-
-	isync
-	slbie	r6
-BEGIN_FTR_SECTION
-	slbie	r6		/* Workaround POWER5 < DD2.1 issue */
-END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)
-	slbmte	r7,r0
-	isync
-2:
-#endif /* CONFIG_PPC_64S_HASH_MMU */
+	bl	pin_stack_slb
+END_MMU_FTR_SECTION_IFCLR(MMU_FTR_TYPE_RADIX)
+#endif
 
 	clrrdi	r7, r8, THREAD_SHIFT	/* base of new stack */
 	/* Note: this uses SWITCH_FRAME_SIZE rather than INT_FRAME_SIZE