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Date:   Mon, 11 Jul 2022 15:22:35 +0200
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Subject: Re: [PATCH v12 3/3] KVM: s390: resetting the Topology-Change-Report
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To:     Pierre Morel <pmorel@linux.ibm.com>, kvm@vger.kernel.org
Cc:     linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        borntraeger@de.ibm.com, frankja@linux.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: <20220711084148.25017-1-pmorel@linux.ibm.com>
 <20220711084148.25017-4-pmorel@linux.ibm.com>
From:   Janis Schoetterl-Glausch <scgl@linux.ibm.com>
In-Reply-To: <20220711084148.25017-4-pmorel@linux.ibm.com>
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On 7/11/22 10:41, 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>

Reviewed-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>

See nits/comments below.

> ---
>  Documentation/virt/kvm/api.rst   | 25 ++++++++++++++
>  arch/s390/include/uapi/asm/kvm.h |  1 +
>  arch/s390/kvm/kvm-s390.c         | 56 ++++++++++++++++++++++++++++++++
>  include/uapi/linux/kvm.h         |  1 +
>  4 files changed, 83 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)

Is the architecture allowed to extend STSI without a facility?
If so, if we say here that STSI 15.1.x is passed to user space, then
I think we should have a

if (sel1 != 1)
	goto out_no_data;

or maybe even

if (sel1 != 1 || sel2 < 2 || sel2 > 6)
	goto out_no_data;

in priv.c

> +instruction to the userland hypervisor.
> +
> +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

get or set, now that there is no explicit clear anymore.

> +Topology Report (MTCR) bit of the SCA through the kvm_device_attr
> +structure.> +
> +When getting the Modified Change Topology Report value, the attr->addr

When getting/setting the...

> +must point to a byte where the value will be stored.

... will be stored/retrieved from.
> +
>  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..a73cf01a1606 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
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 70436bfff53a..b18e0b940b26 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: CAP_S390_CPU_TOPOLOGY %s",
> +			 r ? "(not available)" : "(success)");
> +		break;
>  	default:
>  		r = -EINVAL;
>  		break;
> @@ -1717,6 +1734,36 @@ 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)

kvm_s390_set_topology_changed maybe?
kvm_s390_get_topology_changed below then.

> +{
> +	if (!test_kvm_facility(kvm, 11))
> +		return -ENXIO;
> +
> +	kvm_s390_update_topology_change_report(kvm, !!attr->attr);
> +	return 0;
> +}
> +
> +static int kvm_s390_get_topology(struct kvm *kvm, struct kvm_device_attr *attr)
> +{
> +	union sca_utility utility;
> +	struct bsca_block *sca;
> +	__u8 topo;
> +
> +	if (!test_kvm_facility(kvm, 11))
> +		return -ENXIO;
> +
> +	read_lock(&kvm->arch.sca_lock);
> +	sca = kvm->arch.sca;
> +	utility.val = READ_ONCE(sca->utility.val);

I don't think you need the READ_ONCE anymore, now that there is a lock it should act as a compile barrier.
> +	read_unlock(&kvm->arch.sca_lock);
> +	topo = utility.mtcr;
> +
> +	if (copy_to_user((void __user *)attr->addr, &topo, sizeof(topo)))

Why void not u8?

> +		return -EFAULT;
> +
> +	return 0;
> +}
> +
[...]