arm64: use alternative auto-nop

Make use of the new alternative_if and alternative_else_nop_endif and
get rid of our homebew NOP sleds, making the code simpler to read.

Note that for cpu_do_switch_mm the ret has been moved out of the
alternative sequence, and in the default case there will be three
additional NOPs executed.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/entry.S

@@ -150,13 +150,7 @@
 	ldr	x23, [sp, #S_SP]		// load return stack pointer
 	msr	sp_el0, x23
 #ifdef CONFIG_ARM64_ERRATUM_845719
-alternative_if_not ARM64_WORKAROUND_845719
-	nop
-	nop
-#ifdef CONFIG_PID_IN_CONTEXTIDR
-	nop
-#endif
-alternative_else
+alternative_if ARM64_WORKAROUND_845719
 	tbz	x22, #4, 1f
 #ifdef CONFIG_PID_IN_CONTEXTIDR
 	mrs	x29, contextidr_el1
@@ -165,7 +159,7 @@ alternative_else
 	msr contextidr_el1, xzr
 #endif
 1:
-alternative_endif
+alternative_else_nop_endif
 #endif
 	.endif
 	msr	elr_el1, x21			// set up the return data

arch/arm64/lib/copy_page.S

@@ -29,14 +29,11 @@
  *	x1 - src
  */
 ENTRY(copy_page)
-alternative_if_not ARM64_HAS_NO_HW_PREFETCH
-	nop
-	nop
-alternative_else
+alternative_if ARM64_HAS_NO_HW_PREFETCH
 	# Prefetch two cache lines ahead.
 	prfm    pldl1strm, [x1, #128]
 	prfm    pldl1strm, [x1, #256]
-alternative_endif
+alternative_else_nop_endif
 
 	ldp	x2, x3, [x1]
 	ldp	x4, x5, [x1, #16]
@@ -52,11 +49,9 @@ alternative_endif
 1:
 	subs	x18, x18, #128
 
-alternative_if_not ARM64_HAS_NO_HW_PREFETCH
-	nop
-alternative_else
+alternative_if ARM64_HAS_NO_HW_PREFETCH
 	prfm    pldl1strm, [x1, #384]
-alternative_endif
+alternative_else_nop_endif
 
 	stnp	x2, x3, [x0]
 	ldp	x2, x3, [x1]

arch/arm64/mm/proc.S

@@ -127,17 +127,12 @@ ENTRY(cpu_do_switch_mm)
 	bfi	x0, x1, #48, #16		// set the ASID
 	msr	ttbr0_el1, x0			// set TTBR0
 	isb
-alternative_if_not ARM64_WORKAROUND_CAVIUM_27456
-	ret
-	nop
-	nop
-	nop
-alternative_else
+alternative_if ARM64_WORKAROUND_CAVIUM_27456
 	ic	iallu
 	dsb	nsh
 	isb
+alternative_else_nop_endif
 	ret
-alternative_endif
 ENDPROC(cpu_do_switch_mm)
 
 	.pushsection ".idmap.text", "ax"