linux-kernel - Re: [Qemu-devel] [PATCH 2/2] kvm: exit to userspace with reason KVM_EXIT_VCPU

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Date:	Sun, 27 Nov 2011 12:50:00 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Liu Ping Fan <kernelfans@...il.com>, aliguori@...ibm.com,
	kvm@...r.kernel.org, qemu-devel@...gnu.org,
	linux-kernel@...r.kernel.org, ryanh@...ibm.com, jan.kiszka@....de
Subject: Re: [Qemu-devel] [PATCH 2/2] kvm: exit to userspace with reason
 KVM_EXIT_VCPU_DEAD

On Sun, Nov 27, 2011 at 12:36:55PM +0200, Avi Kivity wrote:
> On 11/27/2011 04:42 AM, Liu Ping Fan wrote:
> > From: Liu Ping Fan <pingfank@...ux.vnet.ibm.com>
> >
> > The vcpu can be safely released when
> > --1.guest tells us that the vcpu is not needed any longer.
> > --2.vcpu hits the last instruction _halt_
> >
> > If both of the conditions are satisfied, kvm exits to userspace
> > with the reason vcpu dead. So the user thread can exit safely.
> >
> >
> 
> Seems to be completely unnecessary.  If you want to exit from the vcpu
> thread, send it a signal.
> 
Also if guest "tells us that the vcpu is not needed any longer" (via
ACPI I presume) and vcpu actually doing something critical instead of
sitting in 1:hlt; jmp 1b loop then it is guest's problem if it stops
working after vcpu destruction.

--
			Gleb.
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