Messages in this thread | | | Date | Mon, 19 Nov 2018 09:38:55 +0100 | From | Ingo Molnar <> | Subject | Re: STIBP by default.. Revert? |
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* Linus Torvalds <torvalds@linux-foundation.org> wrote:
> This was marked for stable, and honestly, nowhere in the discussion > did I see any mention of just *how* bad the performance impact of this > was.
Yeah. This was an oversight - we'll fix it!
> When performance goes down by 50% on some loads, people need to start > asking themselves whether it was worth it. It's apparently better to > just disable SMT entirely, which is what security-conscious people do > anyway. > > So why do that STIBP slow-down by default when the people who *really* > care already disabled SMT? > > I think we should use the same logic as for L1TF: we default to > something that doesn't kill performance. Warn once about it, and let > the crazy people say "I'd rather take a 50% performance hit than > worry about a theoretical issue".
Yeah, absolutely.
We'll also require performance measurements in changelogs enabling any sort of mitigation feature from now on - this requirement was implicit but 53c613fe6349 flew in under the radar, so it's going to be explicit an explicit requirement.
Thanks,
Ingo
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