linux-kernel - Re: [PATCH] arm64: move kimage_vaddr to .rodata

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Message-ID: <20200312164035.GA21120@lakrids.cambridge.arm.com>
Date:   Thu, 12 Mar 2020 16:40:36 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Rémi Denis-Courmont <remi@...lab.net>
Cc:     linux-arm-kernel@...ts.infradead.org, suzuki.poulose@....com,
        maz@...nel.org, linux-kernel@...r.kernel.org, james.morse@....com,
        catalin.marinas@....com, will@...nel.org,
        kvmarm@...ts.cs.columbia.edu, julien.thierry.kdev@...il.com,
        ard.biesheuvel@...aro.org
Subject: Re: [PATCH] arm64: move kimage_vaddr to .rodata

On Thu, Mar 12, 2020 at 11:40:02AM +0200, Rémi Denis-Courmont wrote:
> From: Remi Denis-Courmont <remi.denis.courmont@...wei.com>
> 
> This datum is not referenced from .idmap.text: it does not need to be
> mapped in idmap. Lets move it to .rodata as it is never written to after
> early boot of the primary CPU.
> (Maybe .data.ro_after_init would be cleaner though?)

Can we move this into arch/arm64/mm/mmu.c, where we already have
kimage_voffset:

| u64 kimage_voffset __ro_after_init;
| EXPORT_SYMBOL(kimage_voffset);

... or is it not possible to initialize kimage_vaddr correctly in C?

Thanks,
Mark.

> 
> Signed-off-by: Rémi Denis-Courmont <remi@...lab.net>
> ---
>  arch/arm64/kernel/head.S | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index 6e08ee2b4d55..8e5c0e0040e4 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -457,17 +457,19 @@ SYM_FUNC_START_LOCAL(__primary_switched)
>  	b	start_kernel
>  SYM_FUNC_END(__primary_switched)
>  
> +	.pushsection ".rodata", "a"
> +SYM_DATA_START(kimage_vaddr)
> +	.quad		_text - TEXT_OFFSET
> +SYM_DATA_END(kimage_vaddr)
> +EXPORT_SYMBOL(kimage_vaddr)
> +	.popsection
> +
>  /*
>   * end early head section, begin head code that is also used for
>   * hotplug and needs to have the same protections as the text region
>   */
>  	.section ".idmap.text","awx"
>  
> -SYM_DATA_START(kimage_vaddr)
> -	.quad		_text - TEXT_OFFSET
> -SYM_DATA_END(kimage_vaddr)
> -EXPORT_SYMBOL(kimage_vaddr)
> -
>  /*
>   * If we're fortunate enough to boot at EL2, ensure that the world is
>   * sane before dropping to EL1.
> -- 
> 2.25.1
> 
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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