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

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Date:	Wed, 25 Jul 2012 13:17:23 +0200
From:	Andre Przywara <andre.przywara@....com>
To:	Vladimir Davydov <vdavydov@...allels.com>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Borislav Petkov <bp@...64.org>,
	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 01:02 PM, Vladimir Davydov wrote:
> On 07/25/2012 02:58 PM, Andre Przywara wrote:
>> On 07/25/2012 12:31 PM, Vladimir Davydov wrote:
>>> On 07/24/2012 04:44 PM, Alan Cox wrote:
>>>>> This approach does not need any kernel support (except for the
>>>>> /proc/cpuinfo filtering). Does this address the issues you have?
>>>> You can do the /proc/cpuinfo filtering in user space too
>>>>
>>> How?
>> I wanted to write the same reply yesterday, but followed the hint in
>> Alan's previous mail:
>> # mount --bind /dev/shm/faked_cpuinfo /somepath/proc/cpuinfo
>>
>> I checked it, it works even with chroots and is not visible from within.
>
> If CPUs go online/offline?

Do you support CPU offlining from within the guest? My OpenVZ guest only 
has /sys/class and nothing else, so I cannot offline any CPU.

So you setup a "hand-crafted" cpuinfo for the guest and this should stay 
valid for the whole guest's runtime, right?

And since it is a dumped file, "host" CPU off/onlining does not affect 
it. Or do you want to propagate this to the guests?
(Sorry, but my thinking is more Xen/KVM oriented, where guests can only 
do most things if they are explicitly allowed to do it and separation 
between guests and host is much stricter).


Regards,
Andre.

-- 
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany

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