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Re: [WARNING] Intel Skylake/Kaby Lake processors: broken hyper-threading

(updates, hopefully the last ones...)

On Sun, 25 Jun 2017, Henrique de Moraes Holschuh wrote:
> Fast-forward a few months, and Mark Shinwell noticed the mention of a
> possible fix for a microcode defect with unknown hit-ratio in the
> intel-microcode package changelog.  He matched it to the issues the
> OCaml community were observing, verified that the microcode fix indeed
> solved the OCaml issue, and contacted the Debian maintainer about it.

There are a few factual incorrections in the advisory text, which were
entirely my fault, and for which I apologise.  The corrections are

1. It was one of the OCaml bug reporters (by the handle of ygrek) who
   first noticed that the 20170511 microcode update could be relevant,
   and not Mark Shinwell.

2. Various other bug reporters and OCaml developers, some under request
   from Mark and some by their own volition, helped out and devoted
   substantial time to investigating the issue.

I apologise to those involved: to "ygrek" for misreading the bug report
and attributing to Mark Shinwell the correlation between the SKL150
erratum description and the OCaml compiler issue report; and to all
members of the OCaml community that worked on the issue both in the bug
report and behind the scenes, for not explicitly crediting their effort.

The original OCaml bug report is listed in the references section at the
end of the advisory (and also in this update).

> Related processor signatures and microcode revisions:
> Skylake   : 0x406e3, 0x506e3 (fixed in revision 0xb9/0xba and later,
>                               public fix in linux microcode 20170511)
> Skylake   : 0x50654          (no information, erratum listed)
> Kaby Lake : 0x806e9, 0x906e9 (defect still exists in revision 0x48,
>                               fix available as a BIOS/UEFI update)

The recently launched "Kaby Lake-X" processors (signature 0x906e9,
socket LGA2066) are documented by Intel as *NOT* being affected by the
KBL095 defect.  This information comes from table 16 of the latest
revision of the "7th gen. Core Family specification update" (which is
listed in the references section).

Please note that the "7th gen. Core i7 X-series processors" (Kaby
Lake-X) both support hyper-threading and share the processor signature
(family, model number and stepping) with "Kaby Lake-H/S" processors.
The tests in the advisory (and also the perl script) will *incorrectly*
report Kaby Lake-X processors as affected.


  Henrique Holschuh

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