linux-kernel - Re: [PATCH] x86/bugs: Fix handling when srso mitigation is disabled

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Message-ID: <20240904170225.hoccrhqhinr724au@treble>
Date: Wed, 4 Sep 2024 10:02:25 -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] x86/bugs: Fix handling when srso mitigation is disabled

On Wed, Sep 04, 2024 at 10:07:11AM -0500, David Kaplan wrote:
> When the srso mitigation is disabled, either via mitigations=off or
> spec_rstack_overflow=off, SBPB should be used instead of IBPB if
> possible.  Additionally, move the check earlier in the function so no
> warning is printed about the lack of IBPB-enhancing microcode since the
> user has turned off the mitigation.
> 
> Signed-off-by: David Kaplan <david.kaplan@....com>
> ---
>  arch/x86/kernel/cpu/bugs.c | 14 +++++---------
>  1 file changed, 5 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index 189840db2f8d..10d0775e7aa5 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -2557,10 +2557,9 @@ static void __init srso_select_mitigation(void)
>  {
>  	bool has_microcode = boot_cpu_has(X86_FEATURE_IBPB_BRTYPE);
>  
> -	if (cpu_mitigations_off())
> -		return;
> -
> -	if (!boot_cpu_has_bug(X86_BUG_SRSO)) {
> +	if (!boot_cpu_has_bug(X86_BUG_SRSO) ||
> +	     cpu_mitigations_off() ||
> +	     srso_cmd == SRSO_CMD_OFF) {

These last two lines should be properly indented by shifting left one
space:

	if (!boot_cpu_has_bug(X86_BUG_SRSO) ||
	    cpu_mitigations_off() ||
	    srso_cmd == SRSO_CMD_OFF) {

Otherwise,

Acked-by: Josh Poimboeuf <jpoimboe@...nel.org>

-- 
Josh