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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Mon, 13 May 2019 10:51:52 +0100 Received: from d06av21.portsmouth.uk.ibm.com (d06av21.portsmouth.uk.ibm.com [9.149.105.232]) by b06cxnps3074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x4D9ppCu40239208 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 13 May 2019 09:51:51 GMT Received: from d06av21.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id CA28652057; Mon, 13 May 2019 09:51:50 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.152.97.217]) by d06av21.portsmouth.uk.ibm.com (Postfix) with ESMTP id 77FCE5205F; Mon, 13 May 2019 09:51:50 +0000 (GMT) To: David Hildenbrand , Collin Walling , qemu-devel@nongnu.org, qemu-s390x@nongnu.org, cohuck@redhat.com, rth@twiddle.net, pasic@linux.ibm.com, mst@redhat.com, pbonzini@redhat.com References: <1556749903-19221-1-git-send-email-walling@linux.ibm.com> From: Christian Borntraeger Openpgp: preference=signencrypt Autocrypt: addr=borntraeger@de.ibm.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 19051309-0028-0000-0000-0000036D1283 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19051309-0029-0000-0000-0000242C9ED2 Message-Id: <09293a1c-d000-83a8-46b8-b97ad4fa9774@de.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2019-05-13_06:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1905130071 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [generic] X-Received-From: 148.163.158.5 Subject: Re: [Qemu-devel] [PATCH v4] s390: diagnose 318 info reset and migration support X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 13.05.19 11:40, David Hildenbrand wrote: > On 13.05.19 11:34, Christian Borntraeger wrote: >> >> >> On 13.05.19 10:03, David Hildenbrand wrote: >>>>> + if ((SCCB_SIZE - sizeof(ReadInfo)) / sizeof(CPUEntry) < S390_MAX_CPUS) >>>>> + mc->max_cpus = S390_MAX_CPUS - 8; >>>> >>>> This is too complicated, just set it always to 240. >>>> >>>> However, I am still not sure how to best handle this scenario. One >>>> solution is >>>> >>>> 1. Set it statically to 240 for machine > 4.1 >>>> 2. Keep the old machines unmodifed >>>> 3. Don't indicate the CPU feature for machines <= 4.0 >>>> >>>> #3 is the problematic part, as it mixes host CPU features and machines. >>>> Bad. The host CPU model should always look the same on all machines. I >>>> don't like this. >>>> >>> >>> FWIW, #3 is only an issue when modeling it via the CPU model, like >>> Christian suggested. >>> >>> I suggest the following >>> >>> 1. Set the max #cpus for 4.1 to 240 (already done) >>> 2. Keep it for the other machines unmodified (as suggested by Thomas) >>> 3. Create the layout of the SCCB depending on the machine type (to be done) >>> >>> If we want to model diag318 via a CPU feature (which makes sense for >>> migration): >>> >>> 4. Disable diag318 with a warning if used with a machine < 4.1 >>> >> >> I think there is a simpler solution. It is perfectly fine to fail the startup >> if we cannot fulfil the cpu model. So lets just allow 248 and allow this feature >> also for older machines. And if somebody chooses both at the same time, >> lets fails the startup. > > To which knob do you want to glue the layout of the SCLP response? Like > I described? Do you mean instead of warning and masking the feature off > as I suggested, simply failing? The sclp response will depend on the dia318 cpu model flag. If its on, the sclp response will have it, otherwise not. - host-passthrough: not migration safe anyway - host-model: if the target has diag318 good, otherwise we reject migration > > In that case, -machine ..-4.0 -cpu host will not work on new HW with new > KVM. Just noting. Only if you have 248 CPUs (which is unlikely). My point was to do that for all machine levels.