Re: [PATCH v11 3/3] KVM: s390: resetting the Topology-Change-Report

Pierre Morel
2022-07-04T13:54:22Z

On 7/4/22 11:35, Janis Schoetterl-Glausch wrote:
> On 7/1/22 18:25, 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 | 25 +++++++++++++++
>> arch/s390/include/uapi/asm/kvm.h | 10 ++++++
>> arch/s390/kvm/kvm-s390.c | 53 ++++++++++++++++++++++++++++++++
>> include/uapi/linux/kvm.h | 1 +
>> 4 files changed, 89 insertions(+)
>>
>> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
>> index 11e00a46c610..5e086125d8ad 100644
>> --- a/Documentation/virt/kvm/api.rst
>> +++ b/Documentation/virt/kvm/api.rst
>> @@ -7956,6 +7956,31 @@ 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
>> +PTF instruction with function codes 0 or 1 and the STSI(15,1,x)
>> +instruction to the userland hypervisor.
> The latter only if the user STSI capability is also enabled.

Hum, not sure about this.
we can not set facility 11 and return 3 to STSI(15) for valid selectors.

I think that it was right before, KVM_CAP_S390_CPU_TOPOLOGY and
KVM_CAP_S390_USER_STSI are independent in KVM, userland can turn on one
and not the other.
But KVM proposes both.

Of course it is stupid to turn on only KVM_CAP_S390_CPU_TOPOLOGY but KVM
is not responsible for this userland is.

Otherwise, we need to check on KVM_CAP_S390_USER_STSI before authorizing
KVM_CAP_S390_CPU_TOPOLOGY and that looks even more complicated for me,
or we suppress the KVM_CAP_S390_CPU_TOPOLOGY and implement the all
stsi(15) in the kernel what I really do not think is good because of the
complexity of the userland API

>> +
>> +The stfle facility 11, CPU Topology facility, should not be 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.
>> +
>> +When getting the Modified Change Topology Report value, the attr->addr
>> +must point to a byte where the value will be stored.
>> +
>> 9. Known KVM API problems
>> =========================
>>
>> diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h
>> index 7a6b14874d65..df5e8279ffd0 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 +172,15 @@ 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_MTCR_CLEAR 0
>> +#define KVM_S390_VM_CPU_TOPO_MTCR_SET 1
>> +
>> +struct kvm_cpu_topology {
>> + __u16 mtcr : 1;
>> + __u16 reserved : 15;
>> +};
>
> This is no longer used, is it?

No, I sent the wrong patch it seems!! Sorry for that.
There is nothing more in kvm.h now but the definition for
KVM_S390_VM_CPU_TOPOLOGY

>> +
>> /* 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 ee59b03f2e45..5029fe40adbd 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -606,6 +606,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>> case KVM_CAP_S390_PROTECTED:
>> r = is_prot_virt_host();
>> break;
>> + case KVM_CAP_S390_CPU_TOPOLOGY:
>> + r = test_facility(11);
>> + break;
>> default:
>> r = 0;
>> }
>> @@ -817,6 +820,20 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
>> icpt_operexc_on_all_vcpus(kvm);
>> r = 0;
>> break;
>> + case KVM_CAP_S390_CPU_TOPOLOGY:
>> + r = -EINVAL;
>> + mutex_lock(&kvm->lock);
>> + if (kvm->created_vcpus) {
>> + r = -EBUSY;
>> + } else if (test_facility(11)) {
>> + set_kvm_facility(kvm->arch.model.fac_mask, 11);
>> + set_kvm_facility(kvm->arch.model.fac_list, 11);
>> + r = 0;
>> + }
>> + mutex_unlock(&kvm->lock);
>> + VM_EVENT(kvm, 3, "ENABLE: CPU TOPOLOGY %s",
>
> I still would go for consistency here, "ENABLE: CAP_S390_CPU_TOPOLOGY %s".

Yes, done.

>
>> + r ? "(not available)" : "(success)");
>> + break;
>> default:
>> r = -EINVAL;
>> break;
>> @@ -1716,6 +1733,33 @@ static void kvm_s390_update_topology_change_report(struct kvm *kvm, bool val)
>> read_unlock(&kvm->arch.sca_lock);
>> }
>>
>> +static int kvm_s390_set_topology(struct kvm *kvm, struct kvm_device_attr *attr)
>> +{
>> + if (!test_kvm_facility(kvm, 11))
>> + return -ENXIO;
>> +
>> + kvm_s390_update_topology_change_report(kvm, !!attr->attr);
>
> Will this not be automatically clamped to 0,1 if the argument has type bool?

I do not know, anyway done like this is sure.

>> + return 0;
>> +}
>> +
>> +static int kvm_s390_get_topology(struct kvm *kvm, struct kvm_device_attr *attr)
>> +{
>> + union sca_utility utility;
>> + struct bsca_block *sca = kvm->arch.sca;
>> + __u8 topo;
>> +
>> + if (!test_kvm_facility(kvm, 11))
>> + return -ENXIO;
>> +
> read_lock(&kvm->arch.sca_lock);
> utility.val = READ_ONCE(kvm->arch.sca->utility.val);
> read_unlock(&kvm->arch.sca_lock); >
> And then get rid of the sca declaration.

OK

>> + topo = utility.mtcr;
>> +
>> + if (copy_to_user((void __user *)attr->addr, &topo, sizeof(topo)))
>> + return -EFAULT;
>> +
>> + return 0;
>> +}
>> +
> [...]
>

--
Pierre Morel
IBM Lab Boeblingen