Messages in this thread | | | Date | Fri, 24 Jun 2022 08:50:47 +0200 | From | Janosch Frank <> | Subject | Re: [PATCH v10 3/3] KVM: s390: resetting the Topology-Change-Report |
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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.
> +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
> +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.
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()
> + 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 >
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