Re: [PATCH 2/2] x86: Clear incorrectly forced X86_FEATURE_LAHF_LM flag

Borislav Petkov
2009-08-13T16:19:32Z

On Thu, Aug 13, 2009 at 11:55:32AM -0400, Brian Gerst wrote:

[..]

> > Possibly.  If there were some concern that:
> >
> > - The extra instructions would cause a performance impact, and the
> > test was significantly faster than the clear.
>
> Testing a bit is cheap and MSR accesses are not.

true.

> > - The extra instructions might actually cause more problems if the
> > flag is not set.
>
> These MSRs don't exist on older cpus and will cause a fault, which is
> handled at additional cost.

No, we're ok here since this code is exec'ed on K8s only. The _safe
variants are an additional precaution only.

--
Regards/Gruss,
Boris.

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