From: Florian Weimer <fw@deneb.enyo.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andy Lutomirski <luto@kernel.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andi Kleen <ak@linux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/7] IBRS patch series
References: <cover.1515086770.git.tim.c.chen@linux.intel.com>
        <CA+55aFx+5dUyKRjXEavnxzfXbiQnrmiSCw3PgPtSb+6OP-Qhcg@mail.gmail.com>
Date: Fri, 05 Jan 2018 06:25:29 +0100
In-Reply-To: <CA+55aFx+5dUyKRjXEavnxzfXbiQnrmiSCw3PgPtSb+6OP-Qhcg@mail.gmail.com>
        (Linus Torvalds's message of "Thu, 4 Jan 2018 11:00:14 -0800")
Message-ID: <87shbkx4fq.fsf@mid.deneb.enyo.de>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org

* Linus Torvalds:

> On Thu, Jan 4, 2018 at 9:56 AM, Tim Chen <tim.c.chen@linux.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.