linux-kernel - Re: [BUG] x86 : i486 reporting to be vulnerable to Meltdown/Spectre_V1/Spectre

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Date:   Thu, 8 Feb 2018 22:57:36 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Alan Cox <gnomes@...rguk.ukuu.org.uk>
Cc:     Ondrej Zary <linux@...nbow-software.org>, whiteheadm@....org,
        David Woodhouse <dwmw2@...radead.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jiri Kosina <jikos@...nel.org>, Borislav Petkov <bp@...en8.de>,
        Kees Cook <keescook@...omium.org>,
        Jamie Iles <jamie@...ieiles.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Laura Abbott <labbott@...hat.com>,
        Rik van Riel <riel@...riel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] x86 : i486 reporting to be vulnerable to Meltdown/Spectre_V1/Spectre_V2

On Thu, Feb 8, 2018 at 10:16 PM, Alan Cox <gnomes@...rguk.ukuu.org.uk> wrote:
> On Thu, 8 Feb 2018 16:22:40 +0100
> Arnd Bergmann <arnd@...db.de> wrote:
>
>> On Thu, Feb 8, 2018 at 2:49 PM, Alan Cox <gnomes@...rguk.ukuu.org.uk> wrote:
>> >> What about Pentium II and 3? I'm using 5 such machines (and also a Pentium
>> >> MMX). I've tried a spectre test before and it wasn't reading anything useful.
>> >> Don't know about meltdown. Is there a complete test program? (The web is so
>> >> full of crap that even google can't find anything useful.)
>> >
>> > For x86 speculation came in (as far as I can tell) in
>> >
>> > AMD Am5x86
>> > Cyrix 5x86, but branch predictors are disabled by default according to
>> > the docs
>> > Cyrix 6x86, branch prediction on by default
>> > Pentium Pro
>> >
>> > There are later processors that don't have speculation: Quark series, Nat
>> > Semi/Cyrix Geode, earliest AMD geode (I think), some Intel Atom
>> > processors.
>>
>> Wasn't Am5x86 just a 486 clone? AFAICT, speculation only came with the
>> K6 (Am6x86 aka NexGen Nx6x86)
>
> The AMD 486 was a 486, just like UMC. The Am5x86 was a sort of super 486.
> But you are correct I'm muddling that with the K5 - which does speculate
> or at least some of them do. The K5 branch predictor is software
> controllable via the HWCR MSR but who has one today to test or cares 8)

Right, I completely forgot about the K5.

>> All the Geode are apparently derived from Cyrix 5x86 (I always thought
>
> Not quite all. The older ones are Cyrix 5x86 related which indeed means
> they don't have branch prediction on by default until the LX. Just to
> confuse the AMD Geode NX is basically an Athlon mobile.

This one I knew, I was just not using precise enough language.

      Arnd