linux-kernel - Re: [PATCH] kvm: make vcpu life cycle separated from kvm instance

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Date:	Sun, 4 Dec 2011 19:53:37 +0800
From:	Liu ping fan <kernelfans@...il.com>
To:	Jan Kiszka <jan.kiszka@...mens.com>
Cc:	avi@...hat.com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	aliguori@...ibm.com, gleb@...hat.com
Subject: Re: [PATCH] kvm: make vcpu life cycle separated from kvm instance

On Sat, Dec 3, 2011 at 2:26 AM, Jan Kiszka <jan.kiszka@...mens.com> wrote:
> On 2011-12-02 07:26, Liu Ping Fan wrote:
>> From: Liu Ping Fan <pingfank@...ux.vnet.ibm.com>
>>
>> Currently, vcpu can be destructed only when kvm instance destroyed.
>> Change this to vcpu's destruction taken when its refcnt is zero,
>> and then vcpu MUST and CAN be destroyed before kvm's destroy.
>
> I'm lacking the big picture yet (would be good to have in the change log
> - at least I'm too lazy to read the code):
>
> What increments the refcnt, what decrements it again? IOW, how does user
> space controls the life-cycle of a vcpu after your changes?
>
In local APIC mode, delivering IPI to target APIC, target's refcnt is
incremented, and decremented when finished. At other times, using RCU to
protect the vcpu's reference from its destruction.

If kvm_vcpu is not needed by guest, user space can close the
kvm_vcpu's file
descriptors, and then,if the kvm_vcpu has crossed the period of local
APCI mode's reference,it will be destroyed.

Regards,
ping fan

> Thanks,
> Jan
>
> --
> Siemens AG, Corporate Technology, CT T DE IT 1
> Corporate Competence Center Embedded Linux
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