linux-kernel - Re: [PATCH 1/1] x86/pti: Fix kernel warnings for pti= and nopti cmdline options.

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Date:   Mon, 14 Aug 2023 14:12:17 -0700
From:   Sohil Mehta <sohil.mehta@...el.com>
To:     Jo Van Bulck <jo.vanbulck@...kuleuven.be>,
        <linux-kernel@...r.kernel.org>, <dave.hansen@...ux.intel.com>,
        <luto@...nel.org>, <peterz@...radead.org>, <mingo@...hat.com>
CC:     <x86@...nel.org>, <bp@...en8.de>, <tglx@...utronix.de>,
        <hpa@...or.com>
Subject: Re: [PATCH 1/1] x86/pti: Fix kernel warnings for pti= and nopti
 cmdline options.

On 8/12/2023 8:54 AM, Jo Van Bulck wrote:
>  arch/x86/mm/pti.c | 55 ++++++++++++++++++++++++-----------------------
>  1 file changed, 28 insertions(+), 27 deletions(-)
> 

This version is very similar to the original patch and much simpler.
Sorry about the unnecessary churn.

Apart from the minor nits below,
Reviewed-by: Sohil Mehta <sohil.mehta@...el.com>


> +	if (cpu_mitigations_off())
>  		pti_mode = PTI_FORCE_OFF;
> +	if (pti_mode == PTI_FORCE_OFF) {
>  		pti_print_if_insecure("disabled on command line.");
>  		return;
>  	}

A new line here would be useful.

> +	if (pti_mode == PTI_FORCE_ON) {
> +		pti_print_if_secure("force enabled on command line.");
> +		goto enable;
> +	}
>  
> -autosel:
>  	if (!boot_cpu_has_bug(X86_BUG_CPU_MELTDOWN))
>  		return;
>  enable:
>  	setup_force_cpu_cap(X86_FEATURE_PTI);
>  }
>  

Was there an issue with the flow you had in the original patch? It was
avoiding the goto label and flow was a bit more linear.

> if (pti_mode == PTI_AUTO && !boot_cpu_has_bug(X86_BUG_CPU_MELTDOWN))
>  		return;
> 
> if (pti_mode == PTI_FORCE_ON)
> 	pti_print_if_secure("force enabled on command line.");
> 
> setup_force_cpu_cap(X86_FEATURE_PTI);

Sohil