Messages in this thread | | | Date | Thu, 13 Aug 2009 18:18:54 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH 2/2] x86: Clear incorrectly forced X86_FEATURE_LAHF_LM flag |
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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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