Monday, June 26th 2017

Critical Flaw in HyperThreading Discovered in "Skylake" and "Kaby Lake" CPUs

A critical flaw was discovered in the way Intel implemented its simultaneous multi-threading technology, HyperThreading, on "Skylake" and "Kaby Lake" processors. Being a micro-architecture specific flaw, this could affect all implementations, from low-power mobile chips, to mainstream desktop, high-end desktop, and perhaps even enterprise-segment Xeon processors. At this time, there are no security implications of this flaw.

Intel chronicled this flaw in its micro-architecture errata "SKZ7/SKW144/SKL150/SKX150/SKZ7/KBL095/KBW095," and described it as follows: "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." As an implication, Intel goes on to note that Due to this erratum, the system may experience unpredictable system behavior."
The HyperThreading flaw can be fixed through a micro-code update distributed as a UEFI firmware update. Typically, it becomes the responsibility of DIY PC motherboard, pre-built desktop, and notebook manufacturers, to distribute the update. The issue first came to light in a Debian Linux user mailing-list, although it affects all PC operating systems, not just Linux. Support groups of Debian recommend disabling HyperThreading in the UEFI setup programs of your computers as a temporary workaround, till the micro-code patch is applied. Disabling HyperThreading will reduce performance in multi-threaded apps.
Source: Debian Mailing List
Add your own comment

98 Comments on Critical Flaw in HyperThreading Discovered in "Skylake" and "Kaby Lake" CPUs

#51
EarthDog
trparky
You know, of all people I would think people who hang out here would be the kind of person wouldn't be caught dead using a Dell or HP computer in their homes. Self-built or nothing at all. Building one's own computer was seen as a rite of passage, when one acquires their first merit badge of geekdom.
Meh... they have their uses.. of which 90% of the population seems to enjoy. I mean, even those who race cars (yay car analogy) have daily drivers... be it canned from Ford/Honda, or maybe modified a bit. ;)
Posted on Reply
#52
hapkiman
They make this "critical" flaw sound like your system could go nuclear at any moment. My i7 7700k rig runs great, and has no issues whatsoever. Between my wife and my son, it's being used pretty much non-stop everyday.

Not worried about this at all.
Posted on Reply
#53
ensabrenoir
...what it feels like to be intel right now:


Posted on Reply
#54
Chaitanya
BrainCruser
No they aren't. They are keeping their head down, since Ryzen has a similar problem when using FMA instructions. GCC found them crashing the compiler and producing inaccurate code(deadly flaw).
linustechtips.com/main/topic/788732-ryzen-segmentation-faults-when-compiling-heavy-gcc-linux-loads/
If a certain instruction set is not supported then any code using those instructions is going to crash. Creating an issue out of non supported instructions is dumb.
Posted on Reply
#55
rtwjunkie
PC Gaming Enthusiast
trparky
You know, of all people I would think people who hang out here would be the kind of person wouldn't be caught dead using a Dell or HP computer in their homes. Self-built or nothing at all. Building one's own computer was seen as a rite of passage, when one acquires their first merit badge of geekdom.
Nobody is saying they are a fan of or using OEM PC over self built. But you've got your reasoning wrong. You build yourself because of performance and fun of building, not because of reliability.

Most OEM PC's are designed to be solid, long lasting machines which soldier on for years without maintenance. My work PC is an ancient 10 year old bitch of a Dell that won't die, something I pray for daily, since it is the only way I can get something newer.
Posted on Reply
#56
Solaris17
Dainty Moderator
rtwjunkie
Nobody is saying they are a fan of or using OEM PC over self built. But you've got your reasoning wrong. You build yourself because of performance and fun of building, not because of reliability.

Most OEM PC's are designed to be solid, long lasting machines which soldier on for years without maintenance. My work PC is an ancient 10 year old bitch of a Dell that won't die, something I pray for daily, since it is the only way I can get something newer.
optiplex bby plz
Posted on Reply
#57
RejZoR
oxidized
Yeah i think everyone knows fanboys in here by now :):)
AMD fanboy who hasn't had an AMD since Athlon XP era and is currently running a Core i7 as well. I must be a really lousy AMD fanboy then...
Posted on Reply
#58
TheGuruStud
RejZoR
AMD fanboy who hasn't had an AMD since Athlon XP era and is currently running a Core i7 as well. I must be a really lousy AMD fanboy then...
No need for sarcasm when that's factually true LOL. Real fanboys were slaying pentiums for many years after Athlon XP (and did it again OCing phenom IIs). This haswell crap is the worst CPU I've ever owned. Gimme back my Pentium 233 or OCing monster socket 378 celeron.
Posted on Reply
#60
Ahhzz
ssdpro
Do we have any cases of anything negative happening related to this? I can't believe we should really disable functionality based on nameless "Debian support groups" rather than Intel's specification update errata. Skylake has been around a long time now and forums show remarkable stability with CPU related tasks.
.... wtf.
Posted on Reply
#61
oxidized
RejZoR
AMD fanboy who hasn't had an AMD since Athlon XP era and is currently running a Core i7 as well. I must be a really lousy AMD fanboy then...
Really means nothing
Posted on Reply
#62
Frick
Fishfaced Nincompoop
trparky
You know, of all people I would think people who hang out here would be the kind of person wouldn't be caught dead using a Dell or HP computer in their homes. Self-built or nothing at all. Building one's own computer was seen as a rite of passage, when one acquires their first merit badge of geekdom.
Yeah fifteen years ago when I was a wee lad I had the same thoughts, and then OEMs truly were terrible, but now .... if it works, it works.
Posted on Reply
#63
bug
ssdpro
Do we have any cases of anything negative happening related to this? I can't believe we should really disable functionality based on nameless "Debian support groups" rather than Intel's specification update errata. Skylake has been around a long time now and forums show remarkable stability with CPU related tasks.
Oh you don't have to disable anything. It's just that Debian doesn't distribute microcode because it's "not free", so they won't install the updated microcode (already available) for their users.
Posted on Reply
#64
notb
trparky
You know, of all people I would think people who hang out here would be the kind of person wouldn't be caught dead using a Dell or HP computer in their homes. Self-built or nothing at all. Building one's own computer was seen as a rite of passage, when one acquires their first merit badge of geekdom.
You really don't get this, do you?
1) Not all "enthusiast" or "power users" are into building PCs.
2) Not all of them have time to do this.
3) And some like building their PC and even have time, but simply want e.g. OEM's form factor (they tend to be smaller thanks to custom mobos) or service (Next Business Day or Onsite Service).
This is not the first discussion when you're going on about this "enthusiast build their PCs". Aren't you getting a bit bored by now?

Does an astronomer have to build his telescope? Does a cyclist have to assemble and service his bicycle?
Also, think about just how unjust you are to the whole computing idea. Is "being a computer enthusiast" really about building a PC and running benchmarks?
RejZoR
AMD fanboy who hasn't had an AMD since Athlon XP era and is currently running a Core i7 as well. I must be a really lousy AMD fanboy then...
That's even worse. Being a fanboy of a particular company but having to buy products from competitors, because one's favourites are temporarily behind in technology! Imagine the stress, the frustration building up over the years of using products you hate!
Posted on Reply
#65
RejZoR
Lol, the sarcasm flew right over your head. The reason why I have Core i7 is because to be honest, AMD didn't have really good CPU for nearly a decade. I could wait a bit longer for Ryzen, but I didn't. But if AMD keeps up with current pace, it's very likely my next CPU will be AMD again. My fanboy card only speaks wallet language. The reason why I like how Intel is in absolute shit at the moment is to place them on solid ground and realize they can also be garbage. They've been living in absolute comfort for too long. Some bad PR for Intel is good for customers because AMD can eat into their market and that only means lower prices for everyone. We haven't had god competition for ages in CPU segment. That's why I'm liking problems Intel is having right now with knee jerk reactions with X299 platform as well as other issues. Because they ultimately benefit us, consumers.
Posted on Reply
#66
EarthDog
RejZoR
The reason why I like how Intel is in absolute shit at the moment
wowsas....flair for the dramatic, much?
Posted on Reply
#67
jigar2speed
oxidized
Really means nothing
Don't spin that, it means he uses brains and makes an actual investment.
Posted on Reply
#68
trparky
notb
Is "being a computer enthusiast" really about building a PC and running benchmarks?
YES! It's always been that way. We are a different breed after all. Always tweaking, always pushing our systems just a little bit further to eek out just a little bit more performance. It's been that way for as long as I can remember. There's wouldn't be sites like this site and others like it if it weren't for people wanting to do just that.
Posted on Reply
#69
RejZoR
EarthDog
wowsas....flair for the dramatic, much?
Well, it is. Yes, they have an edge from long term comfy life on laurels, but that's slowly changing with AMD hammering the market on all fronts. Consoles, Ryzen R7, Threadripper, EPYC, on compute front with RX Vega, later this year new APU's, they are securing market that matters the most, corporations, businesses and industry. Gamers were always a side thing, but they bring income. Businesses are what bring sustained income.
Posted on Reply
#70
Mescalamba
Mistral
920 for life!

Seriously though, I'm jumping on the Ryzen train as soon as the end of the year... or next year...
Thinking about the same. I do like Intel CPUs, but their current price politics is serious meh. Ryzen seems as viable choice, but will wait till next year, especially if they manage to upgrade their manufacturing process (or at least polish it a bit).

I have it mostly as gaming platform and rest is just graphics and rendering, thus tasks that do benefit from multi-cores very nicely. As for gaming, yea there is benefit in very high speed of 2 cores, but Ryzen isnt that bad actually. Very few games is actually CPU demanding.
Posted on Reply
#71
RealNeil
Mescalamba
Thinking about the same. I do like Intel CPUs, but their current price politics is serious meh. Ryzen seems as viable choice, but will wait till next year, especially if they manage to upgrade their manufacturing process (or at least polish it a bit).

I have it mostly as gaming platform and rest is just graphics and rendering, thus tasks that do benefit from multi-cores very nicely. As for gaming, yea there is benefit in very high speed of 2 cores, but Ryzen isnt that bad actually. Very few games is actually CPU demanding.
I'm happy with my 1700X choice, (recent build) but I'd be a liar if I didn't also say that my Intel systems run great.

Price to performance comparisons are only good for so long in such a volatile market, and AMD's recent releases have lit a fire under Intel's ass.
Their resting on laurels has been pissing people off for a long time.
Now that we have real competition again we have to wait for it to play out a little and then look at what is fairly priced and high performing.

It's all good for the consumer.
Posted on Reply
#72
hapkiman
Ahhzz
.... wtf.
Like I said, I'm not worried at all about this so-called critical bug. To the average consumer it means very little - that is to 99% of us out there (enthusiasts included), we don't need to do anything. You'll know if something has gone wrong. And it won't be something that is as critical as you might think, or something that is irreparable. All my important stuff is constantly backed up, so I could do a fresh install today, and not lose a single thing other than having to re-download a few games.

This doomsday stuff is nonsense.
Posted on Reply
#73
GreiverBlade
hapkiman
Like I said, I'm not worried at all about this so-called critical bug. To the average consumer it means very little - that is to 99% of us out there (enthusiasts included), we don't need to do anything. You'll know if something has gone wrong. And it won't be something that is as critical as you might think, or something that is irreparable. All my important stuff is constantly backed up, so I could do a fresh install today, and not lose a single thing other than having to re-download a few games.

This doomsday stuff is nonsense.
using my pricing as reference: [joke]well ofc ... you paid a overprice on a X600K to have a X700K that has a flawed HT but since you have no use for it, it's not a biggies ... thus the 104$ more is not an issue either, since you have 2mb and a few Mhz more to justify this :D [/joke]
Posted on Reply
#74
kruk
Why are so many people offended by this warning from Debian? I think it's great that they warn their users (not everyone reads errata). If you do serious work on your PC you cannot afford for it to crash. So you disable HT until microcode update comes out: better be safe than sorry.

If you are not affected by this: good for you, move along now, nothing to see here. And please, show some respect for people putting their time into opensource projects. We all benefit from them ...
Posted on Reply
#75
bug
kruk
Why are so many people offended by this warning from Debian? I think it's great that they warn their users (not everyone reads errata). If you do serious work on your PC you cannot afford for it to crash. So you disable HT until microcode update comes out: better be safe than sorry.

If you are not affected by this: good for you, move along now, nothing to see here. And please, show some respect for people putting their time into opensource projects. We all benefit from them ...
Because any sane distribution is just uploading the fixed firmware into their repositories, thus they don't need to warn users because they're actually fixing the issue? Well, more like propagating the fix from Intel, but the end result is the same.
Plus, the bug is so "serious" it went undetected for an entire generation of CPUs.
Posted on Reply
Add your own comment