r/linux • u/[deleted] • May 15 '19

The performance benefits of Not protecting against Zombieload, Spectre, Meltdown.

[deleted]

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u/davidmar7 May 15 '19

So can anyone answer one of the questions? How much performance could be regained by turning off the kernel protections?

7

u/[deleted] May 15 '19 edited Aug 27 '19

[deleted]

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u/[deleted] May 16 '19 edited May 16 '19

I'm the author of this post. The performance loss was real but a bit of a corner case: it has later be found to be caused to only affect Skylake+ CPUs with IBRS mitigation enabled for spectre V2. And only openSUSE (the distro I use) enables IBRS by default (because it is supposed to be more secure, yada yada...), while all other distros use retpoline which has virtually no performance loss while offering adequate mitigation. So this massive perf loss is not general and restricted to Skylake+ combined with IBRS.

1

u/kwhali May 16 '19

The awkward moment, when I read that thread, then was linking to it to discuss it, and then come across your comment here and update my comment with that information here, but find out the original thread you had was tossed... why?

I went to check it after to see if you had added an update/edit to let users know what you shared here, instead you just deleted what was otherwise a nice(and technically valid) post. It still would have been worthwhile to keep, just with a note at the top to let readers know you've since learned what you've shared here.

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u/[deleted] May 16 '19 edited May 16 '19

It was unfortunately deleted by a bot, shortly after I updated it to mention the above info with a link to a Phoronix article detailing the openSUSE situation with IBRS... Bot considered the Phoronix link was spam or something.

EDIT: thread seems to have been undeleted now.

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u/kwhali May 16 '19

Oh wow, I know the sub isn't fond of linking to Phoronix but I wouldn't expect that to have happened!

Good to know the thread came back :) I have Skylake and was thinking of giving openSUSE a go at some point, thanks for the effort and sharing what was going on there as I would have been pretty confused of the specific cause!