Re: [tip:x86/pti] x86/speculation: Use IBRS if available before calling into firmware

Ingo Molnar
2018-02-19T09:39:33Z

* David Woodhouse <dwmw2@infradead.org> wrote:

> On Mon, 2018-02-19 at 10:20 +0100, Peter Zijlstra wrote:
> >
> > I did not update or otherwise change packages while I was bisecting; the
> > machine is:
> >
> > vendor_id       : GenuineIntel
> > cpu family      : 6
> > model           : 62
> > model name      : Intel(R) Xeon(R) CPU E5-2680 v2 @ 2.80GHz
> > stepping        : 4
> > microcode       : 0x428
>
> That's IVX with a microcode that doesn't *have* IBRS/IBPB. I don't
> think there's a publicly available microcode that does; I assume you
> didn't have one and build it into your kernel for early loading, and
> thus you really weren't even using IBRS here? The code never even gets
> patched in?

Note that PeterZ's boot troubles only match the *symptoms* of the spurious
failures reported by Tim Chen. Your commit wasn't bisected to.

I linked these two reports on the (remote) possibility that they might be related
via some alignment dependent bug somewhere else in the x86 kernel - possibly
completely unrelated to any IBRS/IBPB details.

Thanks,

Ingo