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

[Janis Schoetterl-Glausch]

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@xxxxxxxxxxxxx>
> ---
>  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.
> +
> +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?
> +
>  /* 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".

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