From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from [140.186.70.92] (port=47147 helo=eggs.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1PQPk7-00038V-Ae
	for qemu-devel@nongnu.org; Wed, 08 Dec 2010 14:32:03 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <mtosatti@redhat.com>) id 1PQPk2-0002jD-7I
	for qemu-devel@nongnu.org; Wed, 08 Dec 2010 14:31:59 -0500
Received: from mx1.redhat.com ([209.132.183.28]:24174)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <mtosatti@redhat.com>) id 1PQPk1-0002j7-QX
	for qemu-devel@nongnu.org; Wed, 08 Dec 2010 14:31:54 -0500
Date: Wed, 8 Dec 2010 17:31:28 -0200
From: Marcelo Tosatti <mtosatti@redhat.com>
Message-ID: <20101208193128.GA13021@amt.cnet>
References: <1291644227-22923-1-git-send-email-glommer@redhat.com>
	<1291644227-22923-2-git-send-email-glommer@redhat.com>
	<20101206210401.GB14704@amt.cnet>
	<1291741956.28598.17.camel@mothafucka.localdomain>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1291741956.28598.17.camel@mothafucka.localdomain>
Subject: [Qemu-devel] Re: [PATCH v2 1/2] Do not register kvmclock savevm
 section if kvmclock is disabled.
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Glauber Costa <glommer@redhat.com>
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, avi@redhat.com

On Tue, Dec 07, 2010 at 03:12:36PM -0200, Glauber Costa wrote:
> On Mon, 2010-12-06 at 19:04 -0200, Marcelo Tosatti wrote:
> > On Mon, Dec 06, 2010 at 09:03:46AM -0500, Glauber Costa wrote:
> > > Usually nobody usually thinks about that scenario (me included and specially),
> > > but kvmclock can be actually disabled in the host.
> > > 
> > > It happens in two scenarios:
> > >  1. host too old.
> > >  2. we passed -kvmclock to our -cpu parameter.
> > > 
> > > In both cases, we should not register kvmclock savevm section. This patch
> > > achives that by registering this section only if kvmclock is actually
> > > currently enabled in cpuid.
> > > 
> > > The only caveat is that we have to register the savevm section a little bit
> > > later, since we won't know the final kvmclock state before cpuid gets parsed.
> > 
> > What is the problem of registering the section? Restoring the value if
> > the host does not support it returns an error?
> > 
> > Can't you ignore the error if kvmclock is not reported in cpuid, in the
> > restore handler?
> 
> We can change the restore handler, but not the restore handler of
> binaries that are already out there. The motivation here is precisely to
> address migration to hosts without kvmclock, so it's better to have
> a way to disable, than to count on the fact that the other side will be
> able to ignore it.

OK. Can't you register conditionally on kvmclock cpuid bit at the end of
kvm_arch_init_vcpu, in target-i386/kvm.c?