linux-kernel - Re: [PATCH v4 13/36] x86/bugs: Restructure spectre

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Message-ID: <pl56rfs34temiqmi5guqcnfivrpc7eeq2435btjimtnhaawj7t@2zqh7eufl34c>
Date: Thu, 10 Apr 2025 10:08:47 -0700
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, 
	Brendan Jackman <jackmanb@...gle.com>, Derek Manwaring <derekmn@...zon.com>
Subject: Re: [PATCH v4 13/36] x86/bugs: Restructure spectre_v2 mitigation

On Mon, Mar 10, 2025 at 11:40:00AM -0500, David Kaplan wrote:
> Restructure spectre_v2 to use select/update/apply functions to create
> consistent vulnerability handling.
> 
> The spectre_v2 mitigation may be updated based on the selected retbleed
> mitigation.
> 
> Signed-off-by: David Kaplan <david.kaplan@....com>
> ---
>  arch/x86/kernel/cpu/bugs.c | 79 +++++++++++++++++++++++---------------
>  1 file changed, 48 insertions(+), 31 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index 96cb2ac70245..b4a72ddf159c 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -56,6 +56,8 @@
>  static void __init spectre_v1_select_mitigation(void);
>  static void __init spectre_v1_apply_mitigation(void);
>  static void __init spectre_v2_select_mitigation(void);
> +static void __init spectre_v2_update_mitigation(void);
> +static void __init spectre_v2_apply_mitigation(void);
>  static void __init retbleed_select_mitigation(void);
>  static void __init retbleed_update_mitigation(void);
>  static void __init retbleed_apply_mitigation(void);
> @@ -212,7 +214,12 @@ void __init cpu_select_mitigations(void)
>  	/*
>  	 * After mitigations are selected, some may need to update their
>  	 * choices.
> +	 *
> +	 * Note that retbleed_update_mitigation() relies on the state set by
> +	 * spectre_v2_update_mitigation(); specifically it wants to know about
> +	 * spectre_v2=ibrs.
>  	 */
> +	spectre_v2_update_mitigation();
>  	retbleed_update_mitigation();

I'd suggest moving that dependency comment to above
retbleed_update_mitigaton() and making it more concise:

 	/*
 	 * After mitigations are selected, some may need to update their
 	 * choices.
	 */
	spectre_v2_update_mitigation();
	/* retbleed_update_mitigation() depends on spectre_v2_update_mitigation() */
	retbleed_update_mitigation();

-- 
Josh