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Date: Tue, 06 Dec 2011 16:55:02 +0530
From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
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To: Ingo Molnar <mingo@elte.hu>
CC: Fenghua Yu <fenghua.yu@intel.com>, "Rafael J. Wysocki" <rjw@sisk.pl>,
        Thomas Gleixner <tglx@linutronix.de>, H Peter Anvin <hpa@zytor.com>,
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        Tejun Heo <tj@kernel.org>, Borislav Petkov <bp@amd64.org>,
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Subject: Re: [PATCH v4 0/7] x86: BSP or CPU0 online/offline
References: <1321075592-31600-1-git-send-email-fenghua.yu@intel.com> <20111206084230.GC30062@elte.hu> <20111206085816.GA11116@elte.hu> <4EDDE5D0.7030906@linux.vnet.ibm.com> <20111206103500.GD15966@elte.hu> <4EDDF2DE.7020701@linux.vnet.ibm.com>
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On 12/06/2011 04:17 PM, Srivatsa S. Bhat wrote:

> On 12/06/2011 04:05 PM, Ingo Molnar wrote:
> 
>>
>> * Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> wrote:
>>
>>>> But the hibernation angle should be considered. Hibernation 
>>>> already has to deal with the case where someone physically 
>>>> unplugs a CPU and then resumes from the disk image, right? 
>>>> How does the hibernation code handle that case currently?
>>>
>>> Oh, wait a minute. Are we talking about physical CPU Hotplug 
>>> in between hibernation and restore? AFAIK, currently we don't 
>>> handle that at all. [...]
>>
>> Well, not hotplug, but plain old-fashioned: 'hibernate the box, 
>> take out a CPU physically and thaw' kind of hardware change.
>>
> 
> 
> Well, actually that's what I meant, taking this same idea a bit
> further: hibernate the box, take out a CPU physically, insert a
> slightly different CPU (which needs a different microcode image)
> and thaw.
> 
> In this case, the other patch that I mentioned in my previous mail
> would be required (or an equivalent), because the optimization
> patch which is now in mainline, would apply the same old microcode
> image on this new CPU too, blindly.
> 


By the way, this problem is not tied to CPU0 alone, it exists for any
CPU! (as long as we are talking about plugging in/out CPUs physically).

Regards,
Srivatsa S. Bhat