linux-kernel - Re: [PATCH v2 1/5] x86/bugs: Use early_param for spectre_v2

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Message-ID: <5de5fl7tuo5tobdlck5a7inomwecrmw5lbhtp3ldqsxem2wzfy@4sdzpuu77zqe>
Date: Wed, 27 Aug 2025 14:51:59 -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
Subject: Re: [PATCH v2 1/5] x86/bugs: Use early_param for spectre_v2_user

On Tue, Aug 19, 2025 at 02:21:56PM -0500, David Kaplan wrote:
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -1826,7 +1826,7 @@ enum spectre_v2_mitigation_cmd {
>  
>  static enum spectre_v2_mitigation_cmd spectre_v2_cmd __ro_after_init = SPECTRE_V2_CMD_AUTO;
>  
> -enum spectre_v2_user_cmd {
> +enum spectre_v2_user_mitigation_cmd {
>  	SPECTRE_V2_USER_CMD_NONE,
>  	SPECTRE_V2_USER_CMD_AUTO,
>  	SPECTRE_V2_USER_CMD_FORCE,
> @@ -1836,6 +1836,9 @@ enum spectre_v2_user_cmd {
>  	SPECTRE_V2_USER_CMD_SECCOMP_IBPB,
>  };
>  
> +static enum spectre_v2_user_mitigation_cmd spectre_v2_user_cmd __ro_after_init =
> +	SPECTRE_V2_USER_CMD_AUTO;

Should this default not be dependent on CONFIG_MITIGATION_SPECTRE_V2?

> -static enum spectre_v2_user_cmd __init spectre_v2_parse_user_cmdline(void)
> +static int __init spectre_v2_parse_user_cmdline(char *str)

Should probably swap "parse" and "user" to match the namespace of the
surrounding code, i.e. spectre_v2_user_parse_cmdline().  This is for
parsing the "spectre_v2_user" option after all.

>  {
> -	char arg[20];
> -	int ret, i;
> +	if (!str)
> +		return -EINVAL;
>  
>  	if (!IS_ENABLED(CONFIG_MITIGATION_SPECTRE_V2))
>  		return SPECTRE_V2_USER_CMD_NONE;

This return value no longer makes sense here, as this no longer returns
'enum spectre_v2_user_cmd'.

But also, most of the other mitigations allow you to override the
compile time default with the cmdline.  Might as well allow that here
too for consistency.

-- 
Josh