Re: [BUG] x86 : i486 reporting to be vulnerable to Meltdown/Spectre_V1/Spectre_V2

[Arnd Bergmann]

On Thu, Feb 8, 2018 at 2:49 PM, Alan Cox <gnomes@xxxxxxxxxxxxxxxxxxx> 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