arm64: Move post_ttbr_update_workaround to C code

We will soon need to invoke a CPU-specific function pointer after changing
page tables, so move post_ttbr_update_workaround out into C code to make
this possible.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/assembler.h

@@ -492,19 +492,6 @@ alternative_endif
 	mrs	\rd, sp_el0
 	.endm
 
-/*
- * Errata workaround post TTBRx_EL1 update.
- */
-	.macro	post_ttbr_update_workaround
-#ifdef CONFIG_CAVIUM_ERRATUM_27456
-alternative_if ARM64_WORKAROUND_CAVIUM_27456
-	ic	iallu
-	dsb	nsh
-	isb
-alternative_else_nop_endif
-#endif
-	.endm
-
 /*
  * Arrange a physical address in a TTBR register, taking care of 52-bit
  * addresses.

arch/arm64/kernel/entry.S

@@ -277,7 +277,7 @@ alternative_else_nop_endif
 	 * Cavium erratum 27456 (broadcast TLBI instructions may cause I-cache
 	 * corruption).
 	 */
-	post_ttbr_update_workaround
+	bl	post_ttbr_update_workaround
 	.endif
 1:
 	.if	\el != 0

arch/arm64/mm/context.c

@@ -242,6 +242,15 @@ switch_mm_fastpath:
 		cpu_switch_mm(mm->pgd, mm);
 }
 
+/* Errata workaround post TTBRx_EL1 update. */
+asmlinkage void post_ttbr_update_workaround(void)
+{
+	asm(ALTERNATIVE("nop; nop; nop",
+			"ic iallu; dsb nsh; isb",
+			ARM64_WORKAROUND_CAVIUM_27456,
+			CONFIG_CAVIUM_ERRATUM_27456));
+}
+
 static int asids_init(void)
 {
 	asid_bits = get_cpu_asid_bits();

arch/arm64/mm/proc.S

@@ -146,8 +146,7 @@ ENTRY(cpu_do_switch_mm)
 	phys_to_ttbr x0, x2
 	msr	ttbr0_el1, x2			// now update TTBR0
 	isb
-	post_ttbr_update_workaround
-	ret
+	b	post_ttbr_update_workaround	// Back to C code...
 ENDPROC(cpu_do_switch_mm)
 
 	.pushsection ".idmap.text", "ax"