linux-kernel - Re: [PATCH v3 2/7] x86/retbleed: Simplify the =stuff checks

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Message-ID: <20250524111640.GIaDGqmJrY64FV1ZEo@fat_crate.local>
Date: Sat, 24 May 2025 13:16:40 +0200
From: Borislav Petkov <bp@...en8.de>
To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc: x86@...nel.org, David Kaplan <david.kaplan@....com>,
	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Nikolay Borisov <nik.borisov@...e.com>
Subject: Re: [PATCH v3 2/7] x86/retbleed: Simplify the =stuff checks

On Thu, May 22, 2025 at 06:20:47PM -0700, Pawan Gupta wrote:
> Simplify the nested checks, remove redundant print and comment.
> 
> Reviewed-by: Nikolay Borisov <nik.borisov@...e.com>
> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
> ---
>  arch/x86/kernel/cpu/bugs.c | 24 ++++++++----------------
>  1 file changed, 8 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index 53649df2c4d66c6bd3aa34dec69af9df253bccfc..94d0de3e61aec32b3b67c8d21f89a8c67b93dff3 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -1263,24 +1263,16 @@ static void __init retbleed_update_mitigation(void)
>  	if (!boot_cpu_has_bug(X86_BUG_RETBLEED) || cpu_mitigations_off())
>  		return;
>  
> -	/*
> -	 * retbleed=stuff is only allowed on Intel.  If stuffing can't be used
> -	 * then a different mitigation will be selected below.
> -	 *
> -	 * its=stuff will also attempt to enable stuffing.
> -	 */
> -	if (retbleed_mitigation == RETBLEED_MITIGATION_STUFF ||
> -	    its_mitigation == ITS_MITIGATION_RETPOLINE_STUFF) {
> -		if (spectre_v2_enabled != SPECTRE_V2_RETPOLINE) {
> -			pr_err("WARNING: retbleed=stuff depends on spectre_v2=retpoline\n");
> -			retbleed_mitigation = RETBLEED_MITIGATION_NONE;
> -		} else {
> -			if (retbleed_mitigation != RETBLEED_MITIGATION_STUFF)
> -				pr_info("Retbleed mitigation updated to stuffing\n");
> +	 /* ITS can also enable stuffing */
> +	if (its_mitigation == ITS_MITIGATION_RETPOLINE_STUFF)
> +		retbleed_mitigation = RETBLEED_MITIGATION_STUFF;
>  
> -			retbleed_mitigation = RETBLEED_MITIGATION_STUFF;
> -		}
> +	if (retbleed_mitigation == RETBLEED_MITIGATION_STUFF &&
> +	    spectre_v2_enabled != SPECTRE_V2_RETPOLINE) {
> +		pr_err("WARNING: retbleed=stuff depends on spectre_v2=retpoline\n");
> +		retbleed_mitigation = RETBLEED_MITIGATION_NONE;
>  	}
> +
>  	/*
>  	 * Let IBRS trump all on Intel without affecting the effects of the
>  	 * retbleed= cmdline option except for call depth based stuffing
> 
> -- 

Acked-by: Borislav Petkov (AMD) <bp@...en8.de>

-- 
Regards/Gruss,
    Boris.

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