linux-kernel - Re: [KVM timekeeping 13/35] Perform hardware_enable in CPU

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Date:	Fri, 27 Aug 2010 13:43:52 -1000
From:	Zachary Amsden <zamsden@...hat.com>
To:	Jan Kiszka <jan.kiszka@...mens.com>
CC:	kvm@...r.kernel.org, Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Glauber Costa <glommer@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <johnstul@...ibm.com>, linux-kernel@...r.kernel.org
Subject: Re: [KVM timekeeping 13/35] Perform hardware_enable in CPU_STARTING
 callback

On 08/27/2010 06:32 AM, Jan Kiszka wrote:
> Zachary Amsden wrote:
>    
>> The CPU_STARTING callback was added upstream with the intention
>> of being used for KVM, specifically for the hardware enablement
>> that must be done before we can run in hardware virt.  It had
>> bugs on the x86_64 architecture at the time, where it was called
>> after CPU_ONLINE.  The arches have since merged and the bug is
>> gone.
>>      
> What bugs are you referring to, or since which kernel version is
> CPU_STARTING usable for KVM? I need to encode this into kvm-kmod.
>    

Prior to the x86_64 / i386 merge, CPU_STARTING didn't work the same way 
/ exist in the x86_64 code... most of this is historical guesswork.  At 
some point, the 32/64 versions of the code in smpboot.c got merged and 
now it does.

Binary searching around my tree shows this timeframe:

2.6.11? - 2.6.23 : silver age ; i386 and x86_64 merge underway
    |
2.6.24 : bronze age ; i386 and x86_64 deprecated
    |
2.6.26 : iron age; smpboot_32.c / smpboot_64.c merge
      \
      2.6.28 : CPU_STARTING exists and first used

/me scratches head wondering how this affects operation on older kernels....
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