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  • Skylake / Kabylake hyperthreading bug

    Source : https://lists.debian.org/debian-deve.../msg00308.html


    On 2017-05-29, Mark Shinwell, a core OCaml toolchain developer,contacted the Debian developer responsible for the intel-microcode
    package with key information about a Intel processor issue that could be
    easily triggered by the OCaml compiler.

    The issue was being investigated by the OCaml community since
    2017-01-06, with reports of malfunctions going at least as far back as
    Q2 2016. It was narrowed down to Skylake with hyper-threading, which is
    a strong indicative of a processor defect. Intel was contacted about
    it, but did not provide further feedback as far as we know.

    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.

    Apparently, Intel had indeed found the issue, *documented it* (see
    below) and *fixed it*. There was no direct feedback to the OCaml
    people, so they only found about it later.

    The defect is described by the SKZ7/SKW144/SKL150/SKX150/KBL095/KBW095
    Intel processor errata. As described in official public Intel documentation (processor specification updates)

    TL;DR unfixed Skylake and Kaby Lake processors could, in some situations, dangerously misbehave when hyper-threading is enabled.
    Disable hyper-threading immediately in BIOS/UEFI to work around the problem. Read this advisory for instructions about an Intel-provided fix.
    Last edited by Spaceboy; 26-06-17, 11:26.
    --
    Fractal R4 (shhh!) 3570k, z77x-d3h, 16gb, R9-270X, 240gb SSD, 2tb mirror w/ 60gb cache drive

  • #2
    Might be too edge-case to affect many people, but something worth trying if you get "instability" issues running certain software.

    Note that this is OS agnostic and could affect any OS - it's only the discovery and investigation that's been done on debian.
    --
    Fractal R4 (shhh!) 3570k, z77x-d3h, 16gb, R9-270X, 240gb SSD, 2tb mirror w/ 60gb cache drive

    Comment


    • #3
      What happens when a CPU "dangerously misbehaves", out of interest?
      Originally posted by coiler
      He'll have the local FBI round his house with all that hash!
      Originally posted by BigIan88
      turn off that sexy nonsense
      Originally posted by Salad Soup
      turns out if you touch a stripper too much and try and get back in after being kicked out, they dont like that!

      Comment


      • #4
        Originally posted by omega View Post
        What happens when a CPU "dangerously misbehaves", out of interest?
        it collides with a driver...
        I am not losing weight! I'm getting rid of it. I have no intention of finding it again!

        Growing old is inevitable. Growing up is optional

        Comment


        • #5


          I think it just leads to unpredictable results as any calculations it's doing might be wrong.
          If it's triggered, any software could crash or error - from application layer, to drivers, to kernel.
          --
          Fractal R4 (shhh!) 3570k, z77x-d3h, 16gb, R9-270X, 240gb SSD, 2tb mirror w/ 60gb cache drive

          Comment


          • #6
            "collides" or "colludes"?? A certain Professor at Manchester prefers the word "colludes".
            I've not failed. I've just found 10.000 ways that don't work!
            Dave Burnett

            Comment


            • #7
              Originally posted by omega View Post
              What happens when a CPU "dangerously misbehaves", out of interest?
              I'd add to what others have said about instability with some types of crash can be used by exploits. No evidence of that so for in this case though.

              Comment

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