linux-kernel - Re: [PATCH 2/3] x86/speculation: Support Automatic IBRS

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Date:   Tue, 8 Nov 2022 09:06:50 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Kim Phillips <kim.phillips@....com>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        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>,
        Tony Luck <tony.luck@...el.com>,
        Babu Moger <Babu.Moger@....com>,
        Tom Lendacky <thomas.lendacky@....com>, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] x86/speculation: Support Automatic IBRS

On Mon, Nov 07, 2022 at 03:41:03PM -0800, Dave Hansen wrote:
> On 11/7/22 14:39, Kim Phillips wrote:
> > I've started a version that has AUTOIBRS reuse SPECTRE_V2_EIBRS
> > spectre_v2_mitigation enum, but, so far, it's change to bugs.c
> > looks bigger: 58 lines changed vs. 34 (see below).
> > 
> > Let me know if you want me to send it as a part of a v2 submission
> > after I take care of the kvm CPUID review.
> 
> Thanks for putting that together.  I generally like how this looks.
> 
> I think it probably goes to a _bit_ too much trouble to turn off
> "eibrs,lfence/retpoline".  If someone goes to the trouble of specifying
> those, a warning or pr_info() is probably enough.  You don't need to
> actively override it.

Not, even, just do it. User told you to, it's not technically
impossible, so just go.