linux-kernel - Re: [PATCH] x86: Improve description of IA32_EMULATION_DEFAULT

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Date: Tue, 6 Feb 2024 15:58:23 +0100
From: Borislav Petkov <bp@...en8.de>
To: Hanno Böck <hanno@...eck.de>
Cc: tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: Improve description of
 IA32_EMULATION_DEFAULT_DISABLED

On Tue, Jan 30, 2024 at 10:45:43AM +0100, Hanno Böck wrote:
> The description of the option disables a default, but does not mention
> how to change that default. To make it easier to find out, mention boot
> parameter ia32_emulation.
> 
> Signed-off-by: Hanno Böck <hanno@...eck.de>
> ---
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 5edec175b..a65ff33e0 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -3006,8 +3006,10 @@ config IA32_EMULATION_DEFAULT_DISABLED
>  	depends on IA32_EMULATION
>  	help
>  	  Make IA32 emulation disabled by default. This prevents loading 32-bit
> -	  processes and access to 32-bit syscalls. If unsure, leave it to its
> -	  default value.
> +	  processes and access to 32-bit syscalls. If set, IA32 emulation can be
> +	  re-enabled with the boot parameter ia32_emulation=true.

That sentence should say one can enable it *dynamically* with the cmdline
param.

But this text reads weird: if I want to enable it, then I won't set
IA32_EMULATION_DEFAULT_DISABLED in the first place and I won't have that
problem.

So the use case must be something along the lines of, ia32 emu is
default-disabled at build time but for certain cases where one wants it,
one can still enable it per-boot with a cmdline param.

So what's the story here?

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette