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Mon, 27 Jun 2022 13:30:30 +0000 (GMT) Received: from [9.171.84.214] (unknown [9.171.84.214]) by d06av25.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 27 Jun 2022 13:30:30 +0000 (GMT) Message-ID: <48c10cf4-98c7-9203-3edc-ad88fdd1c7bf@linux.ibm.com> Date: Mon, 27 Jun 2022 15:34:59 +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 3/3] KVM: s390: resetting the Topology-Change-Report Content-Language: en-US To: Janosch Frank , kvm@vger.kernel.org Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, borntraeger@de.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> <20220620125437.37122-4-pmorel@linux.ibm.com> <7d50c2df-7cad-dbc6-baa0-ab647f8dde4e@linux.ibm.com> From: Pierre Morel In-Reply-To: <7d50c2df-7cad-dbc6-baa0-ab647f8dde4e@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: tlq26awHELpvgqGZh5IHmOVRGU3mM--r X-Proofpoint-GUID: ww3NyujDHFH_NWuqPDhyWpHXkvrrPDtj 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=2022-06-27_06,2022-06-24_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxlogscore=999 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 malwarescore=0 phishscore=0 impostorscore=0 suspectscore=0 priorityscore=1501 bulkscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2204290000 definitions=main-2206270058 Precedence: bulk List-ID: X-Mailing-List: linux-s390@vger.kernel.org On 6/24/22 08:50, Janosch Frank wrote: > On 6/20/22 14:54, 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, we give userland the possibility to >> query the MTCR state. >> >> We indicate KVM support for the CPU topology facility with a new >> KVM capability: KVM_CAP_S390_CPU_TOPOLOGY. >> >> Signed-off-by: Pierre Morel >> --- >>   Documentation/virt/kvm/api.rst   | 31 +++++++++++ >>   arch/s390/include/uapi/asm/kvm.h | 10 ++++ >>   arch/s390/kvm/kvm-s390.c         | 96 ++++++++++++++++++++++++++++++++ >>   include/uapi/linux/kvm.h         |  1 + >>   4 files changed, 138 insertions(+) >> >> diff --git a/Documentation/virt/kvm/api.rst >> b/Documentation/virt/kvm/api.rst >> index 11e00a46c610..326f8b7e7671 100644 >> --- a/Documentation/virt/kvm/api.rst >> +++ b/Documentation/virt/kvm/api.rst >> @@ -7956,6 +7956,37 @@ should adjust CPUID leaf 0xA to reflect that >> the PMU is disabled. >>   When enabled, KVM will exit to userspace with KVM_EXIT_SYSTEM_EVENT of >>   type KVM_SYSTEM_EVENT_SUSPEND to process the guest suspend request. >> +8.37 KVM_CAP_S390_CPU_TOPOLOGY >> +------------------------------ >> + >> +:Capability: KVM_CAP_S390_CPU_TOPOLOGY >> +:Architectures: s390 >> +:Type: vm >> + >> +This capability indicates that KVM will provide the S390 CPU Topology >> +facility which consist of the interpretation of the PTF instruction for >> +the Function Code 2 along with interception and forwarding of both the > > Making function code capital surprises me when reading. wanted to highlight FC. I remove it. > >> +PTF instruction with Function Codes 0 or 1 and the STSI(15,1,x) >> +instruction to the userland hypervisor. >> + >> +The stfle facility 11, CPU Topology facility, should not be provided > > s/provided/indicated > OK >> +to the guest without this capability. >> + >> +When this capability is present, KVM provides a new attribute group >> +on vm fd, KVM_S390_VM_CPU_TOPOLOGY. >> +This new attribute allows to get, set or clear the Modified Change >> +Topology Report (MTCR) bit of the SCA through the kvm_device_attr >> +structure. >> + >> +Getting the MTCR bit is realized by using a kvm_device_attr attr >> +entry value of KVM_GET_DEVICE_ATTR and with kvm_device_attr addr >> +entry pointing to the address of a struct kvm_cpu_topology. >> +The value of the MTCR is return by the bit mtcr of the structure. > + >> +When using KVM_SET_DEVICE_ATTR the MTCR is set by using the >> +attr->attr value KVM_S390_VM_CPU_TOPO_MTCR_SET and cleared by >> +using KVM_S390_VM_CPU_TOPO_MTCR_CLEAR. > > I have the feeling that we can drop the two blocks above and we won't > loose information. > >> +/** >> + * 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) > > This is a set operation with the value 0 and that's clearly visible by > the copied code. If you make the utility entry a bitfield you can easily > set 0/1 via one function without doing the bit manipulation by hand. OK > > I.e. please only use one set function. > >> +{ >> +    struct bsca_block *sca = kvm->arch.sca; /* SCA version doesn't >> matter */ >> + >> +    ipte_lock(kvm); >> +    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_MTCR_SET: >> +        kvm_s390_sca_set_mtcr(kvm); >> +        break; >> +    case KVM_S390_VM_CPU_TOPO_MTCR_CLEAR: >> +        kvm_s390_sca_clear_mtcr(kvm); >> +        break; >> +    } > > By having two endpoints here we trade an easy check with having to > access process memory to grab the value we want to set. > > I'm still torn about this. > >> +    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 */ > > Same comments as with the set_mtcr() OK > >> +    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) >> +{ >> +    struct kvm_cpu_topology topo = {}; >> + >> +    if (!test_kvm_facility(kvm, 11)) >> +        return -ENXIO; >> + >> +    topo.mtcr = kvm_s390_sca_get_mtcr(kvm) ? 1 : 0; >> +    if (copy_to_user((void __user *)attr->addr, &topo, sizeof(topo))) >> +        return -EFAULT; >> + >> +    return 0; >> +} >> + >>   static int kvm_s390_vm_set_attr(struct kvm *kvm, struct >> kvm_device_attr *attr) >>   { >>       int ret; >> @@ -1730,6 +1817,9 @@ static int kvm_s390_vm_set_attr(struct kvm *kvm, >> struct kvm_device_attr *attr) >>       case KVM_S390_VM_MIGRATION: >>           ret = kvm_s390_vm_set_migration(kvm, attr); >>           break; >> +    case KVM_S390_VM_CPU_TOPOLOGY: >> +        ret = kvm_s390_set_topology(kvm, attr); >> +        break; >>       default: >>           ret = -ENXIO; >>           break; >> @@ -1755,6 +1845,9 @@ static int kvm_s390_vm_get_attr(struct kvm *kvm, >> struct kvm_device_attr *attr) >>       case KVM_S390_VM_MIGRATION: >>           ret = kvm_s390_vm_get_migration(kvm, attr); >>           break; >> +    case KVM_S390_VM_CPU_TOPOLOGY: >> +        ret = kvm_s390_get_topology(kvm, attr); >> +        break; >>       default: >>           ret = -ENXIO; >>           break; >> @@ -1828,6 +1921,9 @@ static int kvm_s390_vm_has_attr(struct kvm *kvm, >> struct kvm_device_attr *attr) >>       case KVM_S390_VM_MIGRATION: >>           ret = 0; >>           break; >> +    case KVM_S390_VM_CPU_TOPOLOGY: >> +        ret = test_kvm_facility(kvm, 11) ? 0 : -ENXIO; >> +        break; >>       default: >>           ret = -ENXIO; >>           break; >> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h >> index 5088bd9f1922..33317d820032 100644 >> --- a/include/uapi/linux/kvm.h >> +++ b/include/uapi/linux/kvm.h >> @@ -1157,6 +1157,7 @@ struct kvm_ppc_resize_hpt { >>   #define KVM_CAP_VM_TSC_CONTROL 214 >>   #define KVM_CAP_SYSTEM_EVENT_DATA 215 >>   #define KVM_CAP_ARM_SYSTEM_SUSPEND 216 >> +#define KVM_CAP_S390_CPU_TOPOLOGY 217 >>   #ifdef KVM_CAP_IRQ_ROUTING > -- Pierre Morel IBM Lab Boeblingen