linux-kernel - Re: [RFC PATCH v2 1/3] x86: cpu/bugs: update SpectreRSB comments for AMD

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Message-ID: <20241115181005.xxlebbykksmimgqj@jpoimboe>
Date: Fri, 15 Nov 2024 10:10:05 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc: Andrew Cooper <andrew.cooper3@...rix.com>, Amit Shah <amit@...nel.org>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, x86@...nel.org,
	linux-doc@...r.kernel.org, amit.shah@....com,
	thomas.lendacky@....com, bp@...en8.de, tglx@...utronix.de,
	peterz@...radead.org, corbet@....net, mingo@...hat.com,
	dave.hansen@...ux.intel.com, hpa@...or.com, seanjc@...gle.com,
	pbonzini@...hat.com, daniel.sneddon@...ux.intel.com,
	kai.huang@...el.com, sandipan.das@....com,
	boris.ostrovsky@...cle.com, Babu.Moger@....com,
	david.kaplan@....com, dwmw@...zon.co.uk
Subject: Re: [RFC PATCH v2 1/3] x86: cpu/bugs: update SpectreRSB comments for
 AMD

On Fri, Nov 15, 2024 at 09:50:47AM -0800, Pawan Gupta wrote:
> This LGTM.
> 
> I think SPECTRE_V2_EIBRS_RETPOLINE is placed in the wrong leg, it
> doesn't need RSB filling on context switch, and only needs VMEXIT_LITE.
> Does below change on top of your patch look okay?

Yeah, I was wondering about that too.  Since it changes existing
VMEXIT_LITE behavior I'll make it a separate patch.  And I'll probably
do the comment changes in a separate patch as well.

> ---
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index 7b9c0a21e478..d3b9a0d7a2b5 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -1622,6 +1622,7 @@ static void __init spectre_v2_mitigate_rsb(enum spectre_v2_mitigation mode)
>  	case SPECTRE_V2_NONE:
>  		return;
>  
> +	case SPECTRE_V2_EIBRS_RETPOLINE:
>  	case SPECTRE_V2_EIBRS_LFENCE:
>  	case SPECTRE_V2_EIBRS:
>  		if (boot_cpu_has_bug(X86_BUG_EIBRS_PBRSB)) {
> @@ -1630,7 +1631,6 @@ static void __init spectre_v2_mitigate_rsb(enum spectre_v2_mitigation mode)
>  		}
>  		return;
>  
> -	case SPECTRE_V2_EIBRS_RETPOLINE:
>  	case SPECTRE_V2_RETPOLINE:
>  	case SPECTRE_V2_LFENCE:
>  	case SPECTRE_V2_IBRS:

-- 
Josh