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

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Date:   Mon, 7 Nov 2022 16:40:18 -0600
From:   Kim Phillips <kim.phillips@....com>
To:     David Laight <David.Laight@...LAB.COM>,
        'Borislav Petkov' <bp@...en8.de>
Cc:     "x86@...nel.org" <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>,
        Peter Zijlstra <peterz@...radead.org>,
        Tony Luck <tony.luck@...el.com>,
        Babu Moger <Babu.Moger@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] x86/speculation: Support Automatic IBRS

On 11/5/22 6:39 AM, David Laight wrote:
> From: Borislav Petkov
>> Sent: 04 November 2022 21:52
>>
>> On Fri, Nov 04, 2022 at 04:36:50PM -0500, Kim Phillips wrote:
>>>   - Allow for spectre_v2=autoibrs in the kernel command line,
>>>     reverting to auto-selection if the feature isn't available.
>>
>> Why?
>>
>> What the whole logic here should do is enable autoibrs when detected
>> automatically, without the need for the user to even select it as it is
>> the superior mitigation.
> 
> The only useful option is to allow a different option be
> selected for code testing.
> So maybe you want an option for completeness - for when
> an 'even better' option is available.

This is true.

Kim