Re: [PATCH v2 16/18] arm64: entry: Add fake CPU feature for unmapping the kernel at EL0

[Mark Rutland]

On Thu, Nov 30, 2017 at 04:39:44PM +0000, Will Deacon wrote:
> -#ifndef CONFIG_UNMAP_KERNEL_AT_EL0
> -	eret
> -#else
>  	.if	\el == 0
> +alternative_insn eret, nop, ARM64_UNMAP_KERNEL_AT_EL0

Since we patch this eret ...

> +#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
> +alternative_if ARM64_UNMAP_KERNEL_AT_EL0
>  	bne	4f
>  	msr	far_el1, x30
>  	tramp_alias	x30, tramp_exit_native
> @@ -334,10 +336,11 @@ alternative_else_nop_endif
>  4:
>  	tramp_alias	x30, tramp_exit_compat
>  	br	x30
> +alternative_else_nop_endif
> +#endif

... we don't need the alternative here. This code won't be executed when
not needed, and the alternative just bloats the kernel.

We can/should keep the ifdef, though.

Thanks,
Mark.