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Tue, 28 Jun 2022 12:18:13 +0000 (GMT) Received: from [9.171.1.134] (unknown [9.171.1.134]) by b06wcsmtp001.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 28 Jun 2022 12:18:12 +0000 (GMT) Message-ID: <851dd253-8412-ed5f-3a97-980b3a3850cc@linux.ibm.com> Date: Tue, 28 Jun 2022 14:18:12 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.10.0 Subject: Re: [PATCH v10 2/3] KVM: s390: guest support for topology function Content-Language: en-US To: Pierre Morel , kvm@vger.kernel.org Cc: 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, imbrenda@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, wintera@linux.ibm.com, seiden@linux.ibm.com, nrb@linux.ibm.com References: <20220620125437.37122-1-pmorel@linux.ibm.com> <20220620125437.37122-3-pmorel@linux.ibm.com> <207a01aa-d92c-4a17-7b2f-aed59da4ce09@linux.ibm.com> <28c52d15-aa80-09a8-297c-f5ae2b798998@linux.ibm.com> From: Janis Schoetterl-Glausch In-Reply-To: <28c52d15-aa80-09a8-297c-f5ae2b798998@linux.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: U39mibgWYF2jvoj-a8t0PB-VOjEVMuQO X-Proofpoint-ORIG-GUID: wP8SPppf0ltW3jzF3pM1KZQf0cbs0QWn X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.883,Hydra:6.0.517,FMLib:17.11.122.1 definitions=2022-06-28_06,2022-06-24_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 priorityscore=1501 malwarescore=0 suspectscore=0 impostorscore=0 bulkscore=0 mlxlogscore=999 clxscore=1015 adultscore=0 mlxscore=0 lowpriorityscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2204290000 definitions=main-2206280048 Precedence: bulk List-ID: X-Mailing-List: linux-s390@vger.kernel.org On 6/28/22 12:58, Pierre Morel wrote: > > > On 6/28/22 10:59, Janis Schoetterl-Glausch wrote: >> On 6/20/22 14:54, Pierre Morel wrote: >>> We report a topology change to the guest for any CPU hotplug. >>> >>> The reporting to the guest is done using the Multiprocessor >>> Topology-Change-Report (MTCR) bit of the utility entry in the guest's >>> SCA which will be cleared during the interpretation of PTF. >>> >>> On every vCPU creation we set the MCTR bit to let the guest know the >>> next time he uses the PTF with command 2 instruction that the >>> topology changed and that he should use the STSI(15.1.x) instruction >>> to get the topology details. >>> >>> STSI(15.1.x) gives information on the CPU configuration topology. >>> Let's accept the interception of STSI with the function code 15 and >>> let the userland part of the hypervisor handle it when userland >>> support the CPU Topology facility. >>> >>> Signed-off-by: Pierre Morel >>> --- >>>   arch/s390/include/asm/kvm_host.h | 11 ++++++++--- >>>   arch/s390/kvm/kvm-s390.c         | 27 ++++++++++++++++++++++++++- >>>   arch/s390/kvm/priv.c             | 15 +++++++++++---- >>>   arch/s390/kvm/vsie.c             |  3 +++ >>>   4 files changed, 48 insertions(+), 8 deletions(-) >>> >> [...] >> >>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c >>> index 8fcb56141689..95b96019ca8e 100644 >>> --- a/arch/s390/kvm/kvm-s390.c >>> +++ b/arch/s390/kvm/kvm-s390.c >>> @@ -1691,6 +1691,25 @@ static int kvm_s390_get_cpu_model(struct kvm *kvm, struct kvm_device_attr *attr) >>>       return ret; >>>   } >>> >>> +/** >>> + * kvm_s390_sca_set_mtcr >> >> I wonder if there is a better name, kvm_s390_report_topology_change maybe? >> >>> + * @kvm: guest KVM description >>> + * >>> + * Is only relevant if the topology facility is present, >>> + * the caller should check KVM facility 11 >>> + * >>> + * Updates the Multiprocessor Topology-Change-Report to signal >>> + * the guest with a topology change. >>> + */ >>> +static void kvm_s390_sca_set_mtcr(struct kvm *kvm) >>> +{ >> >> Do we need a sca_lock read_section here? If we don't why not? >> Did not see one up the stack, but I might have overlooked something. > > Yes we do. > As I said about your well justified comment in a previous mail, ipte_lock is not the right thing to use here and I will replace with an inter locked update. Not sure I'm understanding you right, you're saying we need both? i.e.: struct bsca_block *sca; read_lock(&vcpu->kvm->arch.sca_lock); sca = kvm->arch.sca; atomic_or(SCA_UTILITY_MTCR, &sca->utility); read_unlock(&vcpu->kvm->arch.sca_lock); Obviously you would need to change the definition of the utility field and could not use a bit field like Janosch suggested, unless you want to use a cmpxchg loop. It's a bit ugly that utility is a two byte value. Maybe there is a nicer way to set that bit, OR (OI, OIY) seem appropriate, but I don't know if they have a nice abstraction in Linux or if you'd need inline asm. > >> >>> +    struct bsca_block *sca = kvm->arch.sca; /* SCA version doesn't matter */ >>> + >>> +    ipte_lock(kvm); >>> +    sca->utility |= SCA_UTILITY_MTCR; >>> +    ipte_unlock(kvm); >>> +} >>> + >> >> [...] >> >