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Message-ID: <20090813161854.GB8534@aftab> Date: Thu, 13 Aug 2009 18:18:54 +0200 From: Borislav Petkov <borislav.petkov@....com> To: Brian Gerst <brgerst@...il.com> CC: Kevin Winchester <kjwinchester@...il.com>, mikpe@...uu.se, mingo@...e.hu, linux-kernel@...r.kernel.org Subject: Re: [PATCH 2/2] x86: Clear incorrectly forced X86_FEATURE_LAHF_LM flag 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. Operating | Advanced Micro Devices GmbH System | Karl-Hammerschmidt-Str. 34, 85609 Dornach b. München, Germany Research | Geschäftsführer: Thomas M. McCoy, Giuliano Meroni Center | Sitz: Dornach, Gemeinde Aschheim, Landkreis München (OSRC) | Registergericht München, HRB Nr. 43632 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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