linux-kernel - Re: [PATCH v3 13/35] x86/bugs: Restructure spectre_v2

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Message-ID: <20250211005338.dqj5sg5sj7repdu6@jpoimboe>
Date: Mon, 10 Feb 2025 16:53:38 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: David Kaplan <david.kaplan@....com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H . Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 13/35] x86/bugs: Restructure spectre_v2_user mitigation

On Wed, Jan 08, 2025 at 02:24:53PM -0600, David Kaplan wrote:
> -	if (retbleed_mitigation == RETBLEED_MITIGATION_UNRET ||
> -	    retbleed_mitigation == RETBLEED_MITIGATION_IBPB) {
> -		if (mode != SPECTRE_V2_USER_STRICT &&
> -		    mode != SPECTRE_V2_USER_STRICT_PREFERRED)
> +	if (spectre_v2_user_stibp != SPECTRE_V2_USER_NONE &&
> +	    (retbleed_mitigation == RETBLEED_MITIGATION_UNRET ||
> +	    retbleed_mitigation == RETBLEED_MITIGATION_IBPB)) {

This adds a hidden dependency on retbleed_update_mitigation()?

Also, that last line should be aligned one more space to the right:

	if (spectre_v2_user_stibp != SPECTRE_V2_USER_NONE &&
	    (retbleed_mitigation == RETBLEED_MITIGATION_UNRET ||
	     retbleed_mitigation == RETBLEED_MITIGATION_IBPB)) {

> +static void __init spectre_v2_user_apply_mitigation(void)
> +{
> +	/* Initialize Indirect Branch Prediction Barrier */
> +	if (boot_cpu_has(X86_FEATURE_IBPB) &&
> +	    spectre_v2_user_ibpb != SPECTRE_V2_USER_NONE) {
> +		setup_force_cpu_cap(X86_FEATURE_USE_IBPB);
>  
> -set_mode:
> -	pr_info("%s\n", spectre_v2_user_strings[mode]);
> +		switch (spectre_v2_user_ibpb) {
> +		case SPECTRE_V2_USER_NONE:
> +			break;

This case can't happen, spectre_v2_user_ibpb was already checked for
!SPECTRE_V2_USER_NONE above.

-- 
Josh