linux-kernel - Re: [PATCH v4 6/7] x86/cpu: Support AMD Automatic IBRS

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Date:   Fri, 2 Dec 2022 09:40:29 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Kim Phillips <kim.phillips@....com>, x86@...nel.org
Cc:     Babu Moger <Babu.Moger@....com>, Borislav Petkov <bp@...en8.de>,
        Borislav Petkov <bp@...e.de>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Joao Martins <joao.m.martins@...cle.com>,
        Jonathan Corbet <corbet@....net>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tony Luck <tony.luck@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Alexey Kardashevskiy <aik@....com>, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 6/7] x86/cpu: Support AMD Automatic IBRS

On 11/30/22 17:50, Kim Phillips wrote:
> @@ -1240,8 +1240,11 @@ static const struct {
>  	{ "retpoline,lfence",	SPECTRE_V2_CMD_RETPOLINE_LFENCE,  false },
>  	{ "retpoline,generic",	SPECTRE_V2_CMD_RETPOLINE_GENERIC, false },
>  	{ "eibrs",		SPECTRE_V2_CMD_EIBRS,		  false },
> +	{ "autoibrs",		SPECTRE_V2_CMD_EIBRS,		  false },
>  	{ "eibrs,lfence",	SPECTRE_V2_CMD_EIBRS_LFENCE,	  false },
> +	{ "autoibrs,lfence",	SPECTRE_V2_CMD_EIBRS_LFENCE,	  false },
>  	{ "eibrs,retpoline",	SPECTRE_V2_CMD_EIBRS_RETPOLINE,	  false },
> +	{ "autoibrs,retpoline",	SPECTRE_V2_CMD_EIBRS_RETPOLINE,	  false },
>  	{ "auto",		SPECTRE_V2_CMD_AUTO,		  false },
>  	{ "ibrs",		SPECTRE_V2_CMD_IBRS,              false },

I don't think we should expose "autoibrs" to end users like this.
"eibrs" means always-on IBRS.  Intel did it first, so gets to name it.
Those are the rules, and it's why we call it "x86_64" and not whatever
Intel's silly name for it was.

Also, expanding the strings:

> +	[SPECTRE_V2_EIBRS_RETPOLINE]		= "Mitigation: Enhanced / Automatic IBRS + Retpolines",

is fine, but adding new user-visible options that we have to document is
not.