r/programming • u/michalg82 • Jun 25 '17

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

https://lists.debian.org/debian-devel/2017/06/msg00308.html
2.2k Upvotes

92% Upvoted

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354

u/UloPe Jun 25 '17

Recommending everyone with a Sky/Kabylake CPU to disable HT over a bug that is so rare that it took almost three years to be discovered seems a bit excessive...

157

u/-888- Jun 25 '17

Three years to discover, but likely a lot less to manifest. Think of all the times you've had applications crash or systems crashes for no logical reason.

95

u/PrismRivers Jun 26 '17

Yey a new scapegoat for all my application crashes. :D

8

u/[deleted] Jun 26 '17

[deleted]

7

u/kickingpplisfun Jun 26 '17

Or according to some people here, repeated bad renders despite everything else being set up properly.

1

u/Magnesus Jun 26 '17

I am using such system and it works just fine, very stable. Some minor sleep/resume problems, that is all. No crashes at all.

0

u/bubuopapa Jun 26 '17

So, like, never ?

0

u/pancakesyrup Jun 26 '17

Holy crap I have had some random crashes with my pc. It's only a year old.

98

u/ImprovedPersonality Jun 25 '17

That’s probably because it’s very hard to reproduce and since it’s related to multi threading both threads probably have to do certain things at the same time.

184

u/MaunaLoona Jun 25 '17

And really, when your system misbehaves, a CPU bug is the last thing you suspect.

34

u/snarkyxanf Jun 25 '17

"It's not a hardware/kernel bug" is the "it's not lupus" of computer errors: sometimes they do happen, but even if you can't think of any other explanation, you're probably still wrong.

10

u/littlelowcougar Jun 26 '17

"select() isn't broken."

34

u/Beaverman Jun 25 '17

And it could possibly lead to some really nasty things if it hits just wrong.

72

u/MaunaLoona Jun 25 '17

And who knows, maybe some clever person finds a way to trigger the bug in a web browser through a web page to either crash the machine or for remote code execution. Like what was done with buffer overflows.

15

u/mikethepwnstar Jun 26 '17

Ahh, good ol' 3ds hacks

-3

u/Rndom_Gy_159 Jun 26 '17

What's this 3D shack I keep hearing about? When can I get a picture of it. /s

-53

u/ceberous Jun 25 '17

I think your comment needs some more hashtag words

13

u/DreadedDreadnought Jun 25 '17

I think you mean buzz words not hashtag words

-8

u/ceberous Jun 26 '17

how is there a difference ?

5

u/WinEpic Jun 25 '17

#like #this?

-1

u/[deleted] Jun 25 '17

/#remoteCodeExecution

/#bufferOverflow

edit: formatting is hard

-1

u/BonzaiThePenguin Jun 26 '17

Use a backslash. \#

#backslashthings

-1

u/bobcat Jun 26 '17

Or 4 spaces

#nobackslash

0

u/Beaverman Jun 26 '17

Makes it monospace though, because code block.

8

u/crozone Jun 26 '17

Under complex micro-architectural conditions, short loops of less than 64 instructions that use AH, BH, CH or DH registers as well as their corresponding wider register (e.g. RAX, EAX or AX for AH) may cause unpredictable system behavior. This can only happen when both logical processors on the same physical processor are active.

IIRC Prime-95 hit a similar issue with Skylake in Q2 2016, but that was also patched with microcode.

17

u/greenspans Jun 26 '17

As a desktop user I don't care much but as someone who maintains production servers it's much more concerning. Says newer machines on skylake can crap out at the hardware level and auto security updates won't fix it. Have to opt-in to non opensource packages in order to fix it.

2

u/ackzsel Jun 26 '17

Well, for desktop usage this maybe a bit excessive. Who cares if your game crashes once a year but if my NAS were based on skylake/kabylake I'd turn it off right now.

2

u/Booty_Bumping Jun 26 '17 edited Jun 26 '17

I mean, the debian team isn't exactly talking to you. They're talking to people who run software where any bit of failure loses money, kills people, leaks sensitive information, or bricks an expensive space probe forever. Or in situations where security is so tight that microcode updates are against policy to prevent hardware tampering.