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Wed, 18 May 2022 10:47:44 +0000 (GMT) Received: from [9.171.22.150] (unknown [9.171.22.150]) by b06wcsmtp001.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 18 May 2022 10:47:44 +0000 (GMT) Message-ID: <93c07dce-a64a-fa1a-f70c-9db22ca53f68@linux.ibm.com> Date: Wed, 18 May 2022 12:51:33 +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 v9 3/3] s390x: KVM: resetting the Topology-Change-Report Content-Language: en-US To: David Hildenbrand , 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, 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: <20220506092403.47406-1-pmorel@linux.ibm.com> <20220506092403.47406-4-pmorel@linux.ibm.com> <76fd0c11-5b9b-0032-183b-54db650f13b1@redhat.com> From: Pierre Morel In-Reply-To: <76fd0c11-5b9b-0032-183b-54db650f13b1@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: gWM6D2RUNeri6TMwnWSmYV-0XgbZd999 X-Proofpoint-ORIG-GUID: pR25ogm1zAWtbYYs3loDU5iJEGD5d6Nv X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.874,Hydra:6.0.486,FMLib:17.11.64.514 definitions=2022-05-18_03,2022-05-17_02,2022-02-23_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 suspectscore=0 mlxlogscore=999 clxscore=1015 bulkscore=0 lowpriorityscore=0 malwarescore=0 mlxscore=0 impostorscore=0 spamscore=0 phishscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2202240000 definitions=main-2205180059 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/12/22 11:31, David Hildenbrand wrote: > On 06.05.22 11:24, Pierre Morel wrote: >> During a subsystem reset the Topology-Change-Report is cleared. >> Let's give userland the possibility to clear the MTCR in the case >> of a subsystem reset. >> >> To migrate the MTCR, let's give userland the possibility to >> query the MTCR state. >> >> Signed-off-by: Pierre Morel >> --- >> arch/s390/include/uapi/asm/kvm.h | 5 ++ >> arch/s390/kvm/kvm-s390.c | 79 ++++++++++++++++++++++++++++++++ >> 2 files changed, 84 insertions(+) >> >> diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h >> index 7a6b14874d65..abdcf4069343 100644 >> --- a/arch/s390/include/uapi/asm/kvm.h >> +++ b/arch/s390/include/uapi/asm/kvm.h >> @@ -74,6 +74,7 @@ struct kvm_s390_io_adapter_req { >> #define KVM_S390_VM_CRYPTO 2 >> #define KVM_S390_VM_CPU_MODEL 3 >> #define KVM_S390_VM_MIGRATION 4 >> +#define KVM_S390_VM_CPU_TOPOLOGY 5 >> >> /* kvm attributes for mem_ctrl */ >> #define KVM_S390_VM_MEM_ENABLE_CMMA 0 >> @@ -171,6 +172,10 @@ struct kvm_s390_vm_cpu_subfunc { >> #define KVM_S390_VM_MIGRATION_START 1 >> #define KVM_S390_VM_MIGRATION_STATUS 2 >> >> +/* kvm attributes for cpu topology */ >> +#define KVM_S390_VM_CPU_TOPO_MTR_CLEAR 0 >> +#define KVM_S390_VM_CPU_TOPO_MTR_SET 1 >> + >> /* for KVM_GET_REGS and KVM_SET_REGS */ >> struct kvm_regs { >> /* general purpose regs for s390 */ >> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c >> index c8bdce31464f..80a1244f0ead 100644 >> --- a/arch/s390/kvm/kvm-s390.c >> +++ b/arch/s390/kvm/kvm-s390.c >> @@ -1731,6 +1731,76 @@ static void kvm_s390_sca_set_mtcr(struct kvm *kvm) >> ipte_unlock(kvm); >> } >> >> +/** >> + * kvm_s390_sca_clear_mtcr >> + * @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_clear_mtcr(struct kvm *kvm) >> +{ >> + struct bsca_block *sca = kvm->arch.sca; /* SCA version doesn't matter */ >> + >> + ipte_lock(kvm); >> + sca->utility &= ~SCA_UTILITY_MTCR; > > > One space too much. > > sca->utility &= ~SCA_UTILITY_MTCR; > >> + ipte_unlock(kvm); >> +} >> + >> +static int kvm_s390_set_topology(struct kvm *kvm, struct kvm_device_attr *attr) >> +{ >> + if (!test_kvm_facility(kvm, 11)) >> + return -ENXIO; >> + >> + switch (attr->attr) { >> + case KVM_S390_VM_CPU_TOPO_MTR_SET: >> + kvm_s390_sca_set_mtcr(kvm); >> + break; >> + case KVM_S390_VM_CPU_TOPO_MTR_CLEAR: >> + kvm_s390_sca_clear_mtcr(kvm); >> + break; >> + } >> + return 0; >> +} >> + >> +/** >> + * kvm_s390_sca_get_mtcr >> + * @kvm: guest KVM description >> + * >> + * Is only relevant if the topology facility is present, >> + * the caller should check KVM facility 11 >> + * >> + * reports to QEMU the Multiprocessor Topology-Change-Report. >> + */ >> +static int kvm_s390_sca_get_mtcr(struct kvm *kvm) >> +{ >> + struct bsca_block *sca = kvm->arch.sca; /* SCA version doesn't matter */ >> + int val; >> + >> + ipte_lock(kvm); >> + val = !!(sca->utility & SCA_UTILITY_MTCR); >> + ipte_unlock(kvm); >> + >> + return val; >> +} >> + >> +static int kvm_s390_get_topology(struct kvm *kvm, struct kvm_device_attr *attr) >> +{ >> + int mtcr; > > I think we prefer something like u16 when copying to user space. I come back here. I think I prefer to keep the int. the u16 is more than the MTCR but the entire utility field, so what should I do: rename the function to kvm_s390_get_sca_utility() ? and then should I modify the KVM_S390_VM_CPU_TOPOLOGY to KVM_S390_VM_SCA_UTILITY ? I do not like that, I do not think we should report/handle more information than expected/needed. I can mask the MTCR bit and return a u16 with bit 0 (0x8000) set but I find this a little weird I admit an int is may be not optimal. logically I should report a bool but I do not like to report a bool through the UAPI. The more I think about it the more I think an int is OK. Or in the case we want to spare memory space I can create a flag in a u16 but it should theoretically be different than the firmware MTCR bit. Could be 0x0001. But still, it is only to leave during the copy_to_user where the copy of an int may be as good or better than the copy of a u16. So any more opinion on this? Regards, Pierre > >> + >> + if (!test_kvm_facility(kvm, 11)) >> + return -ENXIO; >> + >> + mtcr = kvm_s390_sca_get_mtcr(kvm); >> + if (copy_to_user((void __user *)attr->addr, &mtcr, sizeof(mtcr))) >> + return -EFAULT; >> + >> + return 0; >> +} > > You should probably add documentation, and document that only the last > bit (0x1) has a meaning. > > Apart from that LGTM. > -- Pierre Morel IBM Lab Boeblingen