From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@redhat.com>
Subject: Re: [patch 01/12] [PATCH] kvm-s390: ioctl to switch to user controlled
 virtual machines
Date: Thu, 08 Dec 2011 11:59:39 +0200
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References: <20111208091230.874920251@de.ibm.com>   <20111208091728.908715499@de.ibm.com> <1323336309.3904.12.camel@lappy>  <4EE08721.4060701@redhat.com> <1323338029.3904.15.camel@lappy>
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Cc: Carsten Otte <cotte@de.ibm.com>,
	Marcelo Tossati <mtosatti@redhat.com>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	Cornelia Huck <cornelia.huck@de.ibm.com>,
	KVM <kvm@vger.kernel.org>,
	Joachim von Buttlar <joachim_von_buttlar@de.ibm.com>,
	Jens Freimann <jfrei@de.ibm.com>,
	Constantin Werner <constantin.werner@de.ibm.com>,
	Alexander Graf <agraf@suse.de>,
	Xiantao Zhang <xiantao.zhang@intel.com>
To: Sasha Levin <levinsasha928@gmail.com>
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On 12/08/2011 11:53 AM, Sasha Levin wrote:
> On Thu, 2011-12-08 at 11:45 +0200, Avi Kivity wrote:
> > On 12/08/2011 11:25 AM, Sasha Levin wrote:
> > > On Thu, 2011-12-08 at 10:12 +0100, Carsten Otte wrote:
> > > > plain text document attachment (enable-ucontrol.patch)
> > > > This patch introduces a new config option for user controlled kernel
> > > > virtual machines. It introduces an optional parameter to
> > > > KVM_CREATE_VM in order to create a user controlled virtual machine.
> > > > The parameter is passed to kvm_arch_init_vm for all architectures.
> > > > Valid values for the new parameter are KVM_VM_REGULAR (defined to 0
> > > > for backward compatibility to old KVM_CREATE_VM) and
> > > > KVM_VM_S390_UCONTROL for s390 only.
> > >
> > > Why is it s390 specific? why isn't it KVM_VM_UCONTROL which is currently
> > > only implemented on s390?
> > 
> > It's not possible (or at least very difficult) to implement ucontrol on
> > x86.  For example, to update VMCSs you need privileged instructions.  It
> > might be doable on svm, but there's no point, really.
>
> Might not work for x86, but maybe on arm? ppc? or some other random arch
> that will be added in the future?
>
> No point in limiting it to s390 from day one.

Agree.

> It also makes code a bit cleaner (kvm_main.c shouldn't have arch names
> in the code).

That doesn't bother me.

-- 
error compiling committee.c: too many arguments to function