Re: [Xen-devel] Ongoing/future speculative mitigation work

[Tamas K Lengyel <tamas.k.lengyel@xxxxxxxxx>]

> A solution to this issue was proposed, whereby Xen synchronises siblings
> on vmexit/entry, so we are never executing code in two different
> privilege levels.  Getting this working would make it safe to continue
> using hyperthreading even in the presence of L1TF.  Obviously, its going
> to come in perf hit, but compared to disabling hyperthreading, all its
> got to do is beat a 60% perf hit to make it the preferable option for
> making your system L1TF-proof.

Could you shed some light what tests were done where that 60%
performance hit was observed? We have performed intensive stress-tests
to confirm this but according to our findings turning off
hyper-threading is actually improving performance on all machines we
tested thus far.

Thanks,
Tamas

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