CPU Security Flaws MELTDOWN and SPECTRE

Discussion in 'PC Industry' started by Bondrewd, Jan 2, 2018.

  1. no-X

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    Those „40 %“ for Macs corresponds to disabled HT, too. ("Hyperthreading improves performance for certain workloads by 30 % to 40 %" see chapter 7)
     
  2. Kaotik

    Kaotik Drunk Member
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    https://www.nrc.nl/nieuws/2019/05/14/hackers-mikken-op-het-intel-hart-a3960208

    edit:
    Wired has info on it in English
    https://www.wired.com/story/intel-mds-attack-speculative-execution-buffer/
     
    #362 Kaotik, May 16, 2019
    Last edited: May 16, 2019
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  3. Pressure

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    Indeed, the newest version of Mojave (10.14.5) reports whether or not Hyper-Threading is enabled.

    Hyper-Threading Technology: Enabled
     
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  4. swaaye

    swaaye Entirely Suboptimal
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    The only hyperthreading I have around is in notebooks. Surface Book (6600U), ASUS G750JY (4860HQ) and my ancient ASUS G73JH (920XM). I greatly look forward to seeing what Windows 10 does to them. I imagine the Surface Book will get more firmware updates, though I wonder how much longer MS will keep that up.

    I can't say I've noticed anything sluggish about the old 920XM with up-to-date Win7 or Win10 at this point.
     
    #364 swaaye, May 16, 2019
    Last edited: May 16, 2019
  5. entity279

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    I've the 7980XE . Maybe no HT would be a slight performance improvement in the majority of cases for me.
     
  6. Rootax

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    With all the little regressions here and there, maybe zen+ would be come on top if a lot of reviews were re-done now with all the patches and mitigations in place... ?

    I'm still good with my 5820k OC@4.2 , but honestly, seeing how AMD is non affected by most of this, it's an argument they could push a lot with Zen2...
     
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  7. 3dilettante

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    Phoronix has done some testing across various Intel CPUs with various levels of mitigation enabled. The most recent Intel cores do lose a measurable amount of performance, but many of the vulnerabilities or mitigations hit system calls or context switches, which are already high-overhead. Intel frequently had a commanding lead in those areas, and sometimes even with the losses it's a matter of some ties or a reduced lead versus Zen. Since systems try to avoid these overheads as much as possible, the overall impact outside of some things like IO-heavy loads is minimized.
    The vulnerabilities that may require disabling SMT aren't all Intel-only, and since Zen has shown better SMT scaling it would lose more if SMT is disabled.

    That many workloads still have Intel competitive or leading may mean that the goal for the next microarchitectures is to try to implement many of the Intel speculative measures while mitigating whichever corner case is leaking information. CPU generations fight for single-digit performance gains, so trying to get back 5-10% by restoring known performance improvements is a tempting direction.
     
  8. BRiT

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    At least the shit-show is so bad that the Linux folks are building in a simple boot-time mitigation controls and also allowing for some controls at run-time too.
    • mitigations=off: Disable all mitigations.
    • mitigations=auto: [default] Enable all default mitigations, but leave SMT enabled, even if it's vulnerable.
    • mitigations=auto,nosmt: Enable all default mitigations, disabling SMT if needed by a mitigation.
    instead of:
    • pti=off spectre_v2=off l1tf=off mds=off nospec_store_bypass_disable no_stf_barrier
     
  9. swaaye

    swaaye Entirely Suboptimal
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    Is there a way to disable Hyperthreading with Windows? I was going to disable it on my old G73JH with 920XM but the BIOS has no option.
     
  10. hoom

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    Zen2 includes extra hardware fixes from AMD
    https://www.anandtech.com/show/14525/amd-zen-2-microarchitecture-analysis-ryzen-3000-and-epyc-rome/3
     
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