linux-kernel - Re: [PATCH v2 13/18] arm64: entry: Hook up entry trampoline to exception vectors

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Date:   Fri, 1 Dec 2017 13:53:01 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Will Deacon <will.deacon@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        catalin.marinas@....com, ard.biesheuvel@...aro.org,
        sboyd@...eaurora.org, dave.hansen@...ux.intel.com,
        keescook@...omium.org, msalter@...hat.com, labbott@...hat.com,
        tglx@...utronix.de
Subject: Re: [PATCH v2 13/18] arm64: entry: Hook up entry trampoline to
 exception vectors

On Thu, Nov 30, 2017 at 04:39:41PM +0000, Will Deacon wrote:
>  	.macro kernel_ventry, el, label, regsize = 64
>  	.align 7
> +#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
> +	.if	\el == 0
> +	.if	\regsize == 64
> +	mrs	x30, tpidrro_el0
> +	msr	tpidrro_el0, xzr
> +	.else
> +	mov	x30, xzr

I guess that's just to prevent acccidental leaks if we dump registers
somewhere, since we used x30 as a scratch register?

> +	.macro tramp_alias, dst, sym
> +	mov_q	\dst, TRAMP_VALIAS
> +	add	\dst, \dst, #(\sym - .entry.tramp.text)
> +	.endm

I didn't realise you could refer to sections like this; neat!

Otherwise, looks fine to me.

Thanks,
Mark.