From: Borislav Petkov <borislav.petkov@amd.com>
To: Brian Gerst <brgerst@gmail.com>
Cc: Kevin Winchester <kjwinchester@gmail.com>,
mikpe@it.uu.se, mingo@elte.hu, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] x86: Clear incorrectly forced X86_FEATURE_LAHF_LM flag
Date: Thu, 13 Aug 2009 18:18:54 +0200 [thread overview]
Message-ID: <20090813161854.GB8534@aftab> (raw)
In-Reply-To: <73c1f2160908130855h128c9908h486d583ee9fdcea5@mail.gmail.com>
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
next prev parent reply other threads:[~2009-08-13 16:19 UTC|newest]
Thread overview: 80+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-08-08 11:53 [PATCH] x86: clear incorrectly forced X86_FEATURE_LAHF_LM flag Kevin Winchester
2009-08-08 15:20 ` Borislav Petkov
2009-08-08 15:42 ` Ingo Molnar
2009-08-08 16:15 ` Ingo Molnar
2009-08-08 22:06 ` Kevin Winchester
2009-08-08 23:17 ` [PATCH v2] " Kevin Winchester
2009-08-10 13:12 ` Borislav Petkov
2009-08-10 22:56 ` [PATCH v3] " Kevin Winchester
2009-08-11 9:44 ` Borislav Petkov
2009-08-11 11:36 ` [tip:x86/urgent] x86: Clear " tip-bot for Kevin Winchester
2009-08-11 14:37 ` [PATCH v3] x86: clear " Mikael Pettersson
2009-08-11 14:56 ` Kevin Winchester
2009-08-11 15:51 ` Borislav Petkov
2009-08-11 15:55 ` Kevin Winchester
2009-08-11 16:01 ` Borislav Petkov
2009-08-12 0:15 ` Kevin Winchester
2009-08-12 11:40 ` Borislav Petkov
2009-08-12 23:02 ` Kevin Winchester
2009-08-13 12:23 ` Borislav Petkov
2009-08-13 12:31 ` [PATCH 1/2] x86, msr: Add an AMD wrmsr with exception handling Borislav Petkov
2009-08-13 12:31 ` [PATCH 2/2] x86: Clear incorrectly forced X86_FEATURE_LAHF_LM flag Borislav Petkov
2009-08-13 14:21 ` Brian Gerst
2009-08-13 14:54 ` Kevin Winchester
2009-08-13 15:55 ` Brian Gerst
2009-08-13 16:18 ` Borislav Petkov [this message]
2009-08-13 22:45 ` Kevin Winchester
2009-08-13 15:54 ` Borislav Petkov
2009-08-13 14:57 ` [PATCH v3] x86: clear " Kevin Winchester
2009-08-13 23:24 ` Kevin Winchester
2009-08-14 12:00 ` Borislav Petkov
2009-08-14 12:06 ` [PATCH 1/2] x86, msr: Add a AMD wrmsr with exception handling Borislav Petkov
2009-08-15 17:06 ` [tip:x86/urgent] " tip-bot for Borislav Petkov
2009-08-14 12:06 ` [PATCH 2/2] x86, AMD: Disable wrongly set X86_FEATURE_LAHF_LM CPUID bit Borislav Petkov
2009-08-15 17:06 ` [tip:x86/urgent] " tip-bot for Borislav Petkov
2009-08-16 6:41 ` Ingo Molnar
2009-08-16 20:10 ` Kevin Winchester
2009-08-16 20:51 ` Ingo Molnar
2009-08-16 21:49 ` Borislav Petkov
2009-08-21 17:40 ` H. Peter Anvin
2009-08-22 16:37 ` Borislav Petkov
2009-08-24 20:34 ` H. Peter Anvin
2009-08-25 5:52 ` Borislav Petkov
2009-08-25 6:44 ` H. Peter Anvin
2009-08-30 11:43 ` Borislav Petkov
2009-08-30 11:50 ` [PATCH 1/3] x86, msr: add rd/wrmsr interfaces with preset registers Borislav Petkov
2009-08-30 11:50 ` [PATCH 2/3] x86, msr: rewrite AMD rd/wrmsr variants Borislav Petkov
2009-08-30 20:03 ` H. Peter Anvin
2009-08-30 20:46 ` Borislav Petkov
2009-08-30 20:04 ` H. Peter Anvin
2009-08-30 11:50 ` [PATCH 3/3] x86, AMD: Disable wrongly set X86_FEATURE_LAHF_LM CPUID bit Borislav Petkov
2009-08-30 19:22 ` H. Peter Anvin
2009-08-30 19:30 ` Borislav Petkov
2009-08-30 20:02 ` H. Peter Anvin
2009-08-30 20:29 ` Borislav Petkov
2009-08-30 20:48 ` H. Peter Anvin
2009-08-31 7:34 ` Borislav Petkov
2009-08-31 7:50 ` [PATCH 1/3] x86, msr: add rd/wrmsr interfaces with preset registers Borislav Petkov
2009-08-31 23:37 ` [tip:x86/cpu] x86, msr: Add " tip-bot for Borislav Petkov
2009-09-01 11:05 ` Ingo Molnar
2009-09-01 13:06 ` Borislav Petkov
2009-09-04 14:08 ` Ingo Molnar
2009-09-04 16:26 ` H. Peter Anvin
2009-09-04 17:06 ` [tip:x86/cpu] x86, msr: change msr-reg.o to obj-y, and export its symbols tip-bot for H. Peter Anvin
2009-09-05 9:57 ` Borislav Petkov
2009-09-06 4:41 ` H. Peter Anvin
2009-08-31 23:38 ` [tip:x86/cpu] x86, msr: CFI annotations, cleanups for msr-reg.S tip-bot for H. Peter Anvin
2009-09-03 22:55 ` [PATCH 1/3] x86, msr: add rd/wrmsr interfaces with preset registers Andrew Morton
2009-09-03 22:57 ` H. Peter Anvin
2009-09-03 23:14 ` Andrew Morton
2009-09-03 23:22 ` H. Peter Anvin
2009-09-04 6:39 ` Ingo Molnar
2009-09-04 8:27 ` Borislav Petkov
2009-08-31 7:50 ` [PATCH 2/3] x86, msr: rewrite AMD rd/wrmsr variants Borislav Petkov
2009-08-31 23:37 ` [tip:x86/cpu] x86, msr: Rewrite " tip-bot for Borislav Petkov
2009-08-31 7:50 ` [PATCH 3/3] x86, AMD: Disable wrongly set X86_FEATURE_LAHF_LM CPUID bit Borislav Petkov
2009-08-31 23:37 ` [tip:x86/cpu] " tip-bot for Borislav Petkov
2009-08-31 8:14 ` [PATCH 3/3] " Borislav Petkov
2009-08-31 18:03 ` H. Peter Anvin
2009-08-30 17:07 ` [tip:x86/urgent] " H. Peter Anvin
2009-08-30 19:17 ` Borislav Petkov
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