From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58995) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dIA5X-0002LE-Jp for qemu-devel@nongnu.org; Tue, 06 Jun 2017 04:43:44 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dIA5T-0007d3-NY for qemu-devel@nongnu.org; Tue, 06 Jun 2017 04:43:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39012) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dIA5T-0007cm-Fl for qemu-devel@nongnu.org; Tue, 06 Jun 2017 04:43:39 -0400 References: <20170531193434.6918-1-david@redhat.com> <20170531193434.6918-3-david@redhat.com> <058e655a-af9b-5596-cd67-e2b2eb5701a8@de.ibm.com> From: David Hildenbrand Message-ID: <39fb1b29-64c6-ca70-7248-839914ed290c@redhat.com> Date: Tue, 6 Jun 2017 10:43:34 +0200 MIME-Version: 1.0 In-Reply-To: <058e655a-af9b-5596-cd67-e2b2eb5701a8@de.ibm.com> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v1 2/2] s390x/cpumodel: improve defintion search without an IBC List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Christian Borntraeger , Halil Pasic , jjherne@linux.vnet.ibm.com, qemu-devel@nongnu.org Cc: Cornelia Huck , thuth@redhat.com, Aurelien Jarno , rth@twiddle.net On 06.06.2017 10:39, Christian Borntraeger wrote: > On 06/02/2017 07:28 PM, Halil Pasic wrote: > [...] >> Maybe integrating some of the discussion from above into the commit >> message would be helpful. > > applied with the following patch description Just wanted to ask you to do that :) Thanks! Looks good to me! > > > Currently, under z/VM on a 0x2827, QEMU will detect a 0x2828 if no > IBC value is provided. QEMU will simply take the last model of that HW > generation, which happens to be the BC version. > > Let's improve our search for that case by selecting the latest CPU > definition that matches the CPU type. This for example will avoid > detecting an z13 as a z13s. > > We might still detect a GA2 version on a GA1 system, but as we don't > have further information at hand, there isn't too much we can do about > it. The alternative of always presenting the oldest GA is not backward > compatible, e.g: > You're running on 0x2827 GA2. > Old QEMU version indicated "0x2828 GA1 == 0x2827 GA2". After you updated > QEMU, you suddenly detect "0x2827 GA1". You're previous libvirt guest > might suddenly refuse to run. > > In the end presenting a newer GA level does not matter because: > > 1: All GAX models share the same base feature set. A GAX++ might > support "more features". > 2: Without an IBC, the guest can't detect the GA version. > > If we have no IBC (esp. unblocked_ibc == 0), the IBC we will present > to the guest in read_SCP_info() will be 0. The guest will not know > which GA version it has. The problem of missing IBC propagates. > > If we don't have a feature of the GA++ version, also our guest won't > have it. So in summary, the guest also has no idea of its GA version. > > Signed-off-by: David Hildenbrand > Message-Id: <20170531193434.6918-3-david@redhat.com> > Acked-by: Jason J. Herne > Reviewed-by: Halil Pasic > Signed-off-by: Christian Borntraeger > [improve patch description by reusing mailing list discussion] > > -- Thanks, David