linux-kernel - Re: [PATCH 0/3] x86/speculation: Support Automatic IBRS

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Date:   Fri, 4 Nov 2022 15:06:28 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Kim Phillips <kim.phillips@....com>, x86@...nel.org
Cc:     Borislav Petkov <bp@...en8.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>,
        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 0/3] x86/speculation: Support Automatic IBRS

On 11/4/22 14:36, Kim Phillips wrote:
> The AMD Zen4 core supports a new feature called Automatic IBRS.
> (Indirect Branch Restricted Speculation).
> 
> Enable Automatic IBRS by default if the CPU feature is present.
> It typically provides greater performance over the incumbent
> generic retpolines mitigation.

Could you also share some information on how this differs from EIBRS and
why it needs to exist in parallel to EBIRS?