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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Tue, 26 Nov 2019 07:54:42 -0000 Received: from d06av22.portsmouth.uk.ibm.com (d06av22.portsmouth.uk.ibm.com [9.149.105.58]) by b06cxnps4074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id xAQ7sfuc46858250 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 26 Nov 2019 07:54:41 GMT Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 3469C4C05C; Tue, 26 Nov 2019 07:54:41 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D11624C058; Tue, 26 Nov 2019 07:54:40 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.145.22.13]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 26 Nov 2019 07:54:40 +0000 (GMT) Subject: Re: [PATCH v2 2/2] s390x/cpumodel: Introduce dynamic feature groups To: David Hildenbrand , qemu-devel@nongnu.org References: <20191125172031.16282-1-david@redhat.com> <20191125172031.16282-3-david@redhat.com> From: Christian Borntraeger Autocrypt: addr=borntraeger@de.ibm.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.0 MIME-Version: 1.0 In-Reply-To: <20191125172031.16282-3-david@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 19112607-0008-0000-0000-0000033858FE X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19112607-0009-0000-0000-00004A575B7A Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.95,18.0.572 definitions=2019-11-26_01:2019-11-21,2019-11-26 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 phishscore=0 mlxscore=0 malwarescore=0 impostorscore=0 priorityscore=1501 spamscore=0 adultscore=0 clxscore=1015 bulkscore=0 mlxlogscore=925 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1910280000 definitions=main-1911260070 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [fuzzy] X-Received-From: 148.163.158.5 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Thomas Huth , Janosch Frank , Cornelia Huck , Richard Henderson , Halil Pasic , qemu-s390x@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 25.11.19 18:20, David Hildenbrand wrote: > > As soon as dynamic feature groups are used, the CPU model becomes > migration-unsafe. Upper layers can expand these models to migration-safe > and static variants, allowing them to be migrated. I really dislike that. I am trying to get rid of the unsafe variants (e.g. now defaulting to host-model instead of host-passthrough). I do not want to give users new ways of hurting themselves. Unless I misunderstood Eduardo, I think his versioning approach is actually better in regard to migration, no? I z terms, you can still say -cpu z13 which is just an alias to z13v1 z13v2 etc. Assuming that the version is checked this will be safe.