Messages in this thread | | | Date | Mon, 27 Jun 2022 15:34:59 +0200 | Subject | Re: [PATCH v10 3/3] KVM: s390: resetting the Topology-Change-Report | From | Pierre Morel <> |
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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 <pmorel@linux.ibm.com> >> --- >> 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
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