linux-kernel - Re: [PATCH 0/7] IBRS patch series

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Message-ID: <87shbkx4fq.fsf@mid.deneb.enyo.de>
Date:   Fri, 05 Jan 2018 06:25:29 +0100
From:   Florian Weimer <fw@...eb.enyo.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Tim Chen <tim.c.chen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/7] IBRS patch series

* Linus Torvalds:

> On Thu, Jan 4, 2018 at 9:56 AM, Tim Chen <tim.c.chen@...ux.intel.com> wrote:
>>
>> Speculation on Skylake and later requires these patches ("dynamic IBRS")
>> be used instead of retpoline[1].
>
> Can somebody explain this part?
>
> I was assuming that retpoline would work around this issue on all uarchs.
>
> This seems to say "retpoline does nothing on Skylake+"

Retpoline also looks incompatible with CET, so future Intel CPUs will
eventually need a different approach anyway.