linux-kernel - Re: [PATCH 2/2] cpu: intel, amd: mask cleared cpuid features

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Date:	Wed, 25 Jul 2012 15:39:57 +0400
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Borislav Petkov <bp@...64.org>
CC:	Andre Przywara <andre.przywara@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
	Borislav Petkov <borislav.petkov@....com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andreas Herrmann <andreas.herrmann3@....com>,
	Pavel Emelianov <xemul@...allels.com>,
	Konstantin Khorenko <khorenko@...allels.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH 2/2] cpu: intel, amd: mask cleared cpuid features

On 07/25/2012 02:43 PM, Borislav Petkov wrote:
> On Wed, Jul 25, 2012 at 02:31:23PM +0400, Vladimir Davydov wrote:
>> So, you prefer adding some filtering of /proc/cpuinfo into the
>> mainstream kernel
> That's already there right? And your 1/2 patch was making toggling those
> bits easier.
>
>> (not now, later, for LXC to work) instead of enabling clearcpuid boot
>> option to mask CPUID features? IMO, the latter would look clearer.
> Yes, but for reasons noted earlier, you cannot tweak all hardware CPUID
> features as you want them.
>
> So, having a software-only layer of tweaking /proc/cpuinfo or something
> different you can come up with is the only option you have.
>
> And even in that case, applications running in the container which
> execute CPUID might fail in a strange manner when the corresponding
> /proc/cpuinfo flag was cleared by you intentionally but the hardware
> CPUID flag is there. In such situations, issues like that should
> probably be sorted on a case-by-case basis I guess.
>
> Thanks.
>

We've agreed that tweaking CPUID bits in kernel is not a good idea and 
it is better to think about virtualization of /proc/cpuinfo and using 
msr-tools.

Thank you for your time and feedback.
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