linux-kernel - Re: [RFC v5 56/57] arm64: entry: Avoid empty alternatives entries

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Message-ID: <20200109165145.GI3112@lakrids.cambridge.arm.com>
Date:   Thu, 9 Jan 2020 16:51:46 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Julien Thierry <jthierry@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        jpoimboe@...hat.com, peterz@...radead.org, raphael.gault@....com,
        catalin.marinas@....com, will@...nel.org
Subject: Re: [RFC v5 56/57] arm64: entry: Avoid empty alternatives entries

On Thu, Jan 09, 2020 at 04:02:59PM +0000, Julien Thierry wrote:
> kernel_ventry will create alternative entries to potentially replace
> 0 instructions with 0 instructions for EL1 vectors. While this does not
> cause an issue, it pointlessly takes up some bytes in the alternatives
> section.
> 
> Do not generate such entries.
> 
> Signed-off-by: Julien Thierry <jthierry@...hat.com>

This looks like a sensible cleanup on its own. FWIW:

Acked-by: Mark Rutland <mark.rutland@....com>

Mark.

> ---
>  arch/arm64/kernel/entry.S | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 7c6a0a41676f..605bb7cbe499 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -60,16 +60,16 @@
>  	.macro kernel_ventry, el, label, regsize = 64
>  	.align 7
>  #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
> -alternative_if ARM64_UNMAP_KERNEL_AT_EL0
>  	.if	\el == 0
> +alternative_if ARM64_UNMAP_KERNEL_AT_EL0
>  	.if	\regsize == 64
>  	mrs	x30, tpidrro_el0
>  	msr	tpidrro_el0, xzr
>  	.else
>  	mov	x30, xzr
>  	.endif
> -	.endif
>  alternative_else_nop_endif
> +	.endif
>  #endif
>  
>  	sub	sp, sp, #S_FRAME_SIZE
> -- 
> 2.21.0
>