From mboxrd@z Thu Jan  1 00:00:00 1970
From: Sasha Levin <levinsasha928@gmail.com>
Subject: Re: [patch 01/12] [PATCH] kvm-s390: ioctl to switch to user
 controlled virtual machines
Date: Thu, 08 Dec 2011 11:53:49 +0200
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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: Avi Kivity <avi@redhat.com>
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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.

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

-- 

Sasha.