arm64/kvm: use alternative auto-nop

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

Note that for __kvm_call_hyp the branch to __vhe_hyp_call has been moved
out of the alternative sequence, and in the default case there will be
four additional NOPs executed.

Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: kvmarm@lists.cs.columbia.edu
Acked-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/include/asm/kvm_mmu.h

@@ -99,14 +99,10 @@
 .macro kern_hyp_va	reg
 alternative_if_not ARM64_HAS_VIRT_HOST_EXTN
 	and     \reg, \reg, #HYP_PAGE_OFFSET_HIGH_MASK
-alternative_else
-	nop
-alternative_endif
-alternative_if_not ARM64_HYP_OFFSET_LOW
-	nop
-alternative_else
+alternative_else_nop_endif
+alternative_if ARM64_HYP_OFFSET_LOW
 	and     \reg, \reg, #HYP_PAGE_OFFSET_LOW_MASK
-alternative_endif
+alternative_else_nop_endif
 .endm
 
 #else

arch/arm64/kvm/hyp.S

@@ -46,10 +46,6 @@ alternative_if_not ARM64_HAS_VIRT_HOST_EXTN
 	hvc	#0
 	ldr     lr, [sp], #16
 	ret
-alternative_else
+alternative_else_nop_endif
 	b	__vhe_hyp_call
-	nop
-	nop
-	nop
-alternative_endif
 ENDPROC(__kvm_call_hyp)