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Tue, 28 Jun 2022 15:39:44 +0000 (GMT) Received: from [9.171.41.104] (unknown [9.171.41.104]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 28 Jun 2022 15:39:44 +0000 (GMT) Message-ID: <19e1003f-a6cd-930c-9af3-c21ee04d0395@linux.ibm.com> Date: Tue, 28 Jun 2022 17:44:12 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.3.0 Subject: Re: [PATCH v10 2/3] KVM: s390: guest support for topology function Content-Language: en-US To: Janis Schoetterl-Glausch , 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> <851dd253-8412-ed5f-3a97-980b3a3850cc@linux.ibm.com> <7924cf38-83cb-5d5c-9ad9-a4faaa89f9d5@linux.ibm.com> From: Pierre Morel In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: NK1xlvDM8YdkHH-Vp8j_1fag8GkvxtEK X-Proofpoint-ORIG-GUID: Rs3Iq5dKcpA04M8MTHHqcKKxc27CaZdL 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_07,2022-06-28_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 phishscore=0 mlxlogscore=999 clxscore=1015 bulkscore=0 spamscore=0 mlxscore=0 malwarescore=0 lowpriorityscore=0 impostorscore=0 adultscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2204290000 definitions=main-2206280063 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/28/22 17:01, Janis Schoetterl-Glausch wrote: > On 6/28/22 16:13, Pierre Morel wrote: >> >> >> On 6/28/22 14:18, Janis Schoetterl-Glausch wrote: >>> 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. >> >> I was think to something like this because it is what is used most of the time when a bit is to be change concurrently with firmware. > > Ah, ok you want to keep the bitfield. > > [...] >> >> static void kvm_s390_sca_set_mtcr(struct kvm *kvm, int val) > > If you use a bool val you can simply do new.mtcr = val; below. >> { >>         struct bsca_block *sca = kvm->arch.sca; >>         union sca_utility new, old; >> >>         read_lock(&kvm->arch.sca_lock); > > Don't forget to move the sca = kvm->arch.sca; under the lock here. >>         do { >>                 old = READ_ONCE(sca->utility); >>                 new = old; >>                 new.mtcr = val ? 1 : 0; >>         } while (cmpxchg(&sca->utility.val, old.val, new.val) != old.val); >>         read_lock(&kvm->arch.sca_lock); >> } right, thanks, and to unlock at the end :) >> >>>> >>>>> >>>>>> +    struct bsca_block *sca = kvm->arch.sca; /* SCA version doesn't matter */ >>>>>> + >>>>>> +    ipte_lock(kvm); >>>>>> +    sca->utility |= SCA_UTILITY_MTCR; >>>>>> +    ipte_unlock(kvm); >>>>>> +} >>>>>> + >>>>> >>>>> [...] >>>>> >>>> >>> >> > -- Pierre Morel IBM Lab Boeblingen