linux-kernel - Re: linux-next: Tree for November 22 (kvm)

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Date:	Mon, 29 Nov 2010 11:05:58 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Zachary Amsden <zamsden@...hat.com>
CC:	Avi Kivity <avi@...hat.com>, Glauber Costa <glommer@...hat.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>, kvm@...r.kernel.org,
	linux-next@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: linux-next: Tree for November 22 (kvm)

On 11/29/10 10:08, Zachary Amsden wrote:
> On 11/29/2010 07:52 AM, Randy Dunlap wrote:
>> On 11/29/10 09:47, Zachary Amsden wrote:
>>   
>>> On 11/29/2010 06:35 AM, Avi Kivity wrote:
>>>     
>>>> On 11/29/2010 06:33 PM, Randy Dunlap wrote:
>>>>       
>>>>> On Mon, 22 Nov 2010 13:26:27 -0800 Randy Dunlap wrote:
>>>>>
>>>>>         
>>>>>>   On Mon, 22 Nov 2010 13:49:11 +1100 Stephen Rothwell wrote:
>>>>>>
>>>>>>           
>>>>>>>   Hi all,
>>>>>>>
>>>>>>>   Changes since 20101119:
>>>>>>>              
>>>>>>
>>>>>>   kvm.c:(.init.text+0x11f49): undefined reference to
>>>>>>            
>>>>> `kvm_register_clock'
>>>>>         
>>>>>>   when CONFIG_KVM_CLOCK is not enabled.
>>>>>>            
>>>>>
>>>>> BUild error still present in linux-next-2010-NOV-29.
>>>>>
>>>>>          
>>>> Glauber, Zach?
>>>>
>>>>        
>>> I can only speculate this reference is being called from smpboot without
>>> CONFIG guarding?
>>>      
>> Sorry, looks like I dropped the first line of the error messages:
>>
>> arch/x86/built-in.o: In function `kvm_smp_prepare_boot_cpu':
>> kvm.c:(.init.text+0xad38): undefined reference to `kvm_register_clock'
>>
>> from arch/x86/kernel/kvm.c:
>>
>> #ifdef CONFIG_SMP
>> static void __init kvm_smp_prepare_boot_cpu(void)
>> {
>>     WARN_ON(kvm_register_clock("primary cpu clock"));
>>     kvm_guest_cpu_init();
>>     native_smp_prepare_boot_cpu();
>> }
>>
>> so it looks like you are correct...
>>    
> 
> Looks like this is the appropriate fix:
> 
> #ifdef CONFIG_SMP
> static void __init kvm_smp_prepare_boot_cpu(void)
> {
> #ifdef CONFIG_KVM_CLOCK
>     WARN_ON(kvm_register_clock("primary cpu clock"));
> #endif
>     kvm_guest_cpu_init();
>     native_smp_prepare_boot_cpu();
> }

Sure, that works.  Thanks.

> 
> The SMP code is still buggy as well, wrt printk timing, in that it
> doesn't get called early enough, correct?  Has anyone thought of a good
> solution to that problem?
> 
> Basically the problem is CPU-1 will get CPU-0's per-cpu areas copied
> over, and these are not valid for CPU-1.  If the clocksource is used on
> CPU-1 before kvm clock gets setup, it can go backwards, wreaking havoc,
> causing panic, etc.
> 
> What is the best test to guard against this?  Perhaps we should keep the
> CPU number in the per-cpu data and test against it?


-- 
~Randy
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