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

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Date:   Thu, 8 Feb 2018 16:22:40 +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 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)

All the Geode are apparently derived from Cyrix 5x86 (I always thought
it was a 6x86, but the internet disagrees). For Geode GX, a
specification update at [1] mentions a special procedure for enabling
branch prediction, Geode LX apparently gets this right and always
has branch prediction.

> The more obscure ones - the Transmeta apparently may, the IDT Winchip
> documentation strongly implies it doesn't

The Winchip is what eventually turned into the VIA Nano, which does
have speculative execution, but I don't think the earlier C3 and C7 did,
they are much closer to the original Winchip design.

       Arnd

[1] http://support.amd.com/TechDocs/31533E_gx_2.1_specupdate.pdf