linux-kernel - Re: [PATCH v2 2/4] arm64: remove CONFIG_RODATA_FULL_DEFAULT

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Message-ID: <c1f2ba9e-6f2d-4c7e-9956-6d3b183d3e05@arm.com>
Date: Fri, 6 Dec 2024 10:10:43 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Huang Shijie <shijie@...amperecomputing.com>, catalin.marinas@....com,
 will@...nel.org
Cc: patches@...erecomputing.com, paulmck@...nel.org,
 akpm@...ux-foundation.org, thuth@...hat.com, rostedt@...dmis.org,
 xiongwei.song@...driver.com, ardb@...nel.org, steven.price@....com,
 suzuki.poulose@....com, mark.rutland@....com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 cl@...amperecomputing.com
Subject: Re: [PATCH v2 2/4] arm64: remove CONFIG_RODATA_FULL_DEFAULT_ENABLED

On 11/26/24 14:26, Huang Shijie wrote:
> The default kernel is rodata=on which means

Right but this is true only after the update in the series.

        if (!strcmp(arg, "on")) {
                rodata_enabled = rodata_full = true;
                return true;
        }

rodata_full is always "true" via 'rodata=on' and does not depend
on the config RODATA_FULL_DEFAULT_ENABLED anymore, so it can be
dropped. Please update this commit message with these context as
well.

> CONFIG_RODATA_FULL_DEFAULT_ENABLED is always enabled by default.
> So we can remove CONFIG_RODATA_FULL_DEFAULT_ENABLED now.
> 
> Signed-off-by: Huang Shijie <shijie@...amperecomputing.com>
> ---
>  arch/arm64/Kconfig       | 14 --------------
>  arch/arm64/mm/pageattr.c |  2 +-
>  2 files changed, 1 insertion(+), 15 deletions(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 4316b1fe8bf8..a9ca305a31d8 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1653,20 +1653,6 @@ config MITIGATE_SPECTRE_BRANCH_HISTORY
>  	  When taking an exception from user-space, a sequence of branches
>  	  or a firmware call overwrites the branch history.
>  
> -config RODATA_FULL_DEFAULT_ENABLED
> -	bool "Apply r/o permissions of VM areas also to their linear aliases"
> -	default y
> -	help
> -	  Apply read-only attributes of VM areas to the linear alias of
> -	  the backing pages as well. This prevents code or read-only data
> -	  from being modified (inadvertently or intentionally) via another
> -	  mapping of the same memory page. This additional enhancement can
> -	  be turned off at runtime by passing rodata=[off|on] (and turned on
> -	  with rodata=full if this option is set to 'n')
> -
> -	  This requires the linear region to be mapped down to pages,
> -	  which may adversely affect performance in some cases.
> -
>  config ARM64_SW_TTBR0_PAN
>  	bool "Emulate Privileged Access Never using TTBR0_EL1 switching"
>  	depends on !KCSAN
> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> index 39fd1f7ff02a..6eef08d8451e 100644
> --- a/arch/arm64/mm/pageattr.c
> +++ b/arch/arm64/mm/pageattr.c
> @@ -20,7 +20,7 @@ struct page_change_data {
>  	pgprot_t clear_mask;
>  };
>  
> -bool rodata_full __ro_after_init = IS_ENABLED(CONFIG_RODATA_FULL_DEFAULT_ENABLED);
> +bool rodata_full __ro_after_init = true;
>  
>  bool can_set_direct_map(void)
>  {

This patch can still follow the first one but after folding in the
third patch.