From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:51337) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TOjbp-0002Kz-TQ for qemu-devel@nongnu.org; Thu, 18 Oct 2012 02:29:39 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TOjbp-0000Mm-0J for qemu-devel@nongnu.org; Thu, 18 Oct 2012 02:29:33 -0400 Received: from mail-wi0-f175.google.com ([209.85.212.175]:59681) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TOjbo-0000Mi-Py for qemu-devel@nongnu.org; Thu, 18 Oct 2012 02:29:32 -0400 Received: by mail-wi0-f175.google.com with SMTP id hq4so1290026wib.10 for ; Wed, 17 Oct 2012 23:29:32 -0700 (PDT) Sender: Paolo Bonzini Message-ID: <507FA1C6.2010807@redhat.com> Date: Thu, 18 Oct 2012 08:29:26 +0200 From: Paolo Bonzini MIME-Version: 1.0 References: <507EE07E.20504@redhat.com> <507EFADA.7080700@siemens.com> In-Reply-To: <507EFADA.7080700@siemens.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] Disabling KVM "on the fly" List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jan Kiszka Cc: Clemens Kolbitsch , qemu-devel@nongnu.org Il 17/10/2012 20:37, Jan Kiszka ha scritto: > On 2012-10-17 18:44, Paolo Bonzini wrote: >> Il 17/10/2012 18:37, Clemens Kolbitsch ha scritto: >>> Guys, >>> >>> I know this is question might seem a bit odd, but I'm curious: >>> >>> Has anyone ever tried to write code to disable KVM on the fly / is it >>> at all possible? I have a situation where I need to use TCG for >>> certain parts of the code, but would love to have acceleration for >>> everything else. My idea was to pause the VM, then use the >>> snapshotting mechanism to dump the state, and then to resume the >>> snapshot, but writing the KVM state into the non-KVM structures. >> >> As a start, you can try using "migrate exec:cat>foo.save" with a KVM >> machine and "-incoming 'exec:cat foo.save'" with a TCG machine. The >> main problem should be that TCG doesn't implement kvmclock. >> >> If you disable the KVM interrupt controller and timer (which is just an >> implementation detail, not a hardware difference), > > Unnecessary. Both models (KVM in-kernel and QEMU userspace) are > compatible - in the absence of bugs. He wants to really switch it on the fly---not just migrate out and in---and for that you need to disable the KVM-specific devices. > But loading a KVM image into TCG lets non-trival guests lock up. Likely > due to differences in the CPU virtualization/emulation (MSRs...). Perhaps that can be mitigated by using an older machine model. Start with something simple like a pentium2 and work up from there... Paolo