From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50233) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1e5WeP-0005tt-0i for qemu-devel@nongnu.org; Fri, 20 Oct 2017 08:43:45 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1e5WeL-0006Ag-1z for qemu-devel@nongnu.org; Fri, 20 Oct 2017 08:43:45 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55090) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1e5WeK-0006AN-Rb for qemu-devel@nongnu.org; Fri, 20 Oct 2017 08:43:40 -0400 Date: Fri, 20 Oct 2017 14:43:32 +0200 From: Jiri Denemark Message-ID: <20171020124332.GM130425@orkuz.home> References: <87y3oqugm7.fsf@marc-ibm.boeblingen.de.ibm.com> <20171005121115.GD3946746@orkuz.home> <87y3ok7n2n.fsf@marc-ibm.boeblingen.de.ibm.com> <20171012120714.GA314661@orkuz.home> <87mv4m6pp5.fsf@marc-ibm.boeblingen.de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87mv4m6pp5.fsf@marc-ibm.boeblingen.de.ibm.com> Subject: Re: [Qemu-devel] [libvirt] Question about the host-model CPU mode List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Marc Hartmayer Cc: libvir-list@redhat.com, qemu-devel@nongnu.org, David Hildenbrand , Christian Borntraeger , Boris Fiuczynski , "Jason J. Herne" , Viktor Mihajlovski On Fri, Oct 20, 2017 at 13:09:26 +0200, Marc Hartmayer wrote: > we recently encountered the problem that the 'host-model' [1] has to be > related to the machine type of a domain. We have following problem: > > Let's assume we've a z13 system with a QEMU 2.9 and we define a > domain using the default s390-virtio-ccw machine together with the > host-model CPU mode [1]. The definition will have the machine > expanded to s390-virtio-ccw-2.9 but retain the host-model CPU mode > in the domain definition. In a next step we upgrade to QEMU 2.10 > (first version to recognize z14). Everything is still fine, even > though the machine runs in 2.9 compatibility mode. Finally we > upgrade to a z14. As a consequence it is not possible to start the > domain anymore as the machine type doesn't support our CPU host > model (which is expanded at start time of the domain). > > For determining the actual host-model the QMP command > 'query-cpu-model-expansion' is used. This is done once per QEMU binary > and the result of it is cached by libvirt. The problem with that is > that libvirt queries with the newest machine type of the QEMU binary > for the host CPU model. No, libvirt probes QEMU with -machine none. > We could now either probe the host CPU model for each QEMU binary + > machine type combination and for this we've to start a new QEMU > process each time. This is not really a viable solution. Jirka