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

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Message-ID: <20111204121000.GC12507@redhat.com>
Date:	Sun, 4 Dec 2011 14:10:00 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Liu ping fan <kernelfans@...il.com>
Cc:	Jan Kiszka <jan.kiszka@...mens.com>, avi@...hat.com,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	aliguori@...ibm.com
Subject: Re: [PATCH] kvm: make vcpu life cycle separated from kvm instance

On Sun, Dec 04, 2011 at 07:53:37PM +0800, Liu ping fan wrote:
> 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
Why is this needed?

> 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

--
			Gleb.
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