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Thu, 9 Dec 2021 15:54:19 +0000 (GMT) Received: from osiris (unknown [9.145.184.102]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTPS; Thu, 9 Dec 2021 15:54:19 +0000 (GMT) Date: Thu, 9 Dec 2021 16:54:17 +0100 From: Heiko Carstens To: Claudio Imbrenda Cc: Pierre Morel , kvm@vger.kernel.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, borntraeger@de.ibm.com, frankja@linux.ibm.com, cohuck@redhat.com, david@redhat.com, thuth@redhat.com, gor@linux.ibm.com Subject: Re: [PATCH v5 1/1] s390x: KVM: accept STSI for CPU topology information Message-ID: References: <20211122131443.66632-1-pmorel@linux.ibm.com> <20211122131443.66632-2-pmorel@linux.ibm.com> <20211209133616.650491fd@p-imbrenda> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211209133616.650491fd@p-imbrenda> X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: 3Py32cFlbf1m0w5jzkAF65OWKHlzVEb7 X-Proofpoint-GUID: e4tUfDWOCbKKkIGusBBv---pWWTMFr7K X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.790,Hydra:6.0.425,FMLib:17.11.62.513 definitions=2021-12-09_07,2021-12-08_01,2021-12-02_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 impostorscore=0 bulkscore=0 mlxscore=0 priorityscore=1501 clxscore=1015 lowpriorityscore=0 adultscore=0 suspectscore=0 mlxlogscore=869 malwarescore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2110150000 definitions=main-2112090084 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 09, 2021 at 01:36:16PM +0100, Claudio Imbrenda wrote: > On Mon, 22 Nov 2021 14:14:43 +0100 > Pierre Morel wrote: > > > We let the userland hypervisor know if the machine support the CPU > > topology facility using a new KVM capability: KVM_CAP_S390_CPU_TOPOLOGY. > > > > The PTF instruction will report a topology change if there is any change > > with a previous STSI_15_1_2 SYSIB. > > Changes inside a STSI_15_1_2 SYSIB occur if CPU bits are set or clear > > inside the CPU Topology List Entry CPU mask field, which happens with > > changes in CPU polarization, dedication, CPU types and adding or > > removing CPUs in a socket. > > > > The reporting to the guest is done using the Multiprocessor > > Topology-Change-Report (MTCR) bit of the utility entry of the guest's > > SCA which will be cleared during the interpretation of PTF. > > > > To check if the topology has been modified we use a new field of the > > arch vCPU to save the previous real CPU ID at the end of a schedule > > and verify on next schedule that the CPU used is in the same socket. > > > > We assume in this patch: > > - no polarization change: only horizontal polarization is currently > > used in linux. Why is this assumption necessary? The statement that Linux runs only with horizontal polarization is not true.