Subject: Re: [PATCH v3 03/17] arm64: Turn kaslr_feature_override into a generic SW feature override

From: Catalin Marinas <[email-masked]>
Date: Mon, 12 Jun 2023 18:16:18 +0100

On Fri, Jun 09, 2023 at 05:21:46PM +0100, Marc Zyngier wrote:
> diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
> index 370ab84fd06e..8c93b6198bf5 100644
> --- a/arch/arm64/kernel/idreg-override.c
> +++ b/arch/arm64/kernel/idreg-override.c
> @@ -138,15 +138,11 @@ static const struct ftr_set_desc smfr0 __initconst = {
>  	},
>  };
>  
> -extern struct arm64_ftr_override kaslr_feature_override;
> -
> -static const struct ftr_set_desc kaslr __initconst = {
> -	.name		= "kaslr",
> -#ifdef CONFIG_RANDOMIZE_BASE
> -	.override	= &kaslr_feature_override,
> -#endif
> +static const struct ftr_set_desc sw_features __initconst = {
> +	.name		= "arm64_sw",
> +	.override	= &arm64_sw_feature_override,
>  	.fields		= {
> -		FIELD("disabled", 0, NULL),
> +		FIELD("nokaslr", ARM64_SW_FEATURE_OVERRIDE_NOKASLR, NULL),
>  		{}
>  	},
>  };
> @@ -158,7 +154,7 @@ static const struct ftr_set_desc * const regs[] __initconst = {
>  	&isar1,
>  	&isar2,
>  	&smfr0,
> -	&kaslr,
> +	&sw_features,
>  };
>  
>  static const struct {
> @@ -175,7 +171,7 @@ static const struct {
>  	  "id_aa64isar1.api=0 id_aa64isar1.apa=0 "
>  	  "id_aa64isar2.gpa3=0 id_aa64isar2.apa3=0"	   },
>  	{ "arm64.nomte",		"id_aa64pfr1.mte=0" },
> -	{ "nokaslr",			"kaslr.disabled=1" },
> +	{ "nokaslr",			"arm64_sw.nokaslr=1" },
>  };

I think structuring it as a sw feature makes more sense and I don't
think it breaks anything (as long as people only used "nokaslr").

Reviewed-by: Catalin Marinas <[email-masked]>

As a side note, I was wondering if we should add a SW_FIELD macro to
define width of 1 for such fields (and probably the field extraction
functions need some tweaking) so that we define
ARM64_SW_FEATURE_OVERRIDE_* in increments of 1 rather than 4. Anyway,
that's something to worry if we get too many such software features.

-- 
Catalin

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