linux-kernel - Re: [PATCH v4 1/1] s390x: KVM: accept STSI for CPU topology information

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Date:   Fri, 17 Sep 2021 10:14:25 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     David Hildenbrand <david@...hat.com>, kvm@...r.kernel.org
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        borntraeger@...ibm.com, frankja@...ux.ibm.com, cohuck@...hat.com,
        thuth@...hat.com, imbrenda@...ux.ibm.com, hca@...ux.ibm.com,
        gor@...ux.ibm.com
Subject: Re: [PATCH v4 1/1] s390x: KVM: accept STSI for CPU topology
 information



On 9/16/21 4:03 PM, David Hildenbrand wrote:
>>   struct kvm_vm_stat {
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index 51d1594bd6cd..f3887e13c5db 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -608,6 +608,9 @@ 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;
>>       }
>> @@ -819,6 +822,19 @@ 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:
> 
> As given in my example, this should be
> 
> r = -EINVAL;
> mutex_lock(&kvm->lock);
> if (kvm->created_vcpus) {
>      r = -EBUSY;
> } else if (test_facility(11)) {
> ...
> }
> 
> Similar to how we handle KVM_CAP_S390_VECTOR_REGISTERS.
> 
> [...]
> 
>> +
>> +    /* PTF needs both host and guest facilities to enable 
>> interpretation */
>> +    if (test_kvm_facility(vcpu->kvm, 11) && test_facility(11))
>> +        vcpu->arch.sie_block->ecb |= ECB_PTF;
> 
> This should be simplified to
> 
> if (test_kvm_facility(vcpu->kvm, 11))
> 
> then. (vsie code below is correct)
> 
> 

OK, the idea was to let the hypervisor the possibility to do userland 
emulation if it wanted.
But I can modify as you want.

Regards,
Pierre

-- 
Pierre Morel
IBM Lab Boeblingen