linux-kernel - Re: [PATCH v2 2/2] s390:kvm: Topology expose TOPOLOGY facility

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Date:   Fri, 23 Jul 2021 10:55:56 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>,
        Pierre Morel <pmorel@...ux.ibm.com>, kvm@...r.kernel.org
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        frankja@...ux.ibm.com, david@...hat.com, thuth@...hat.com,
        imbrenda@...ux.ibm.com, hca@...ux.ibm.com, gor@...ux.ibm.com
Subject: Re: [PATCH v2 2/2] s390:kvm: Topology expose TOPOLOGY facility

On Fri, Jul 23 2021, Christian Borntraeger <borntraeger@...ibm.com> wrote:

> On 22.07.21 19:02, Pierre Morel wrote:
>> We add a KVM extension KVM_CAP_S390_CPU_TOPOLOGY to tell the
>> userland hypervisor it is safe to activate the CPU Topology facility.
>
> I think the old variant of using the CPU model was actually better.
> It was just the patch description that was wrong.

I thought we wanted a cap that userspace can enable to get ptf
intercepts? I'm confused.

>   
>> Signed-off-by: Pierre Morel <pmorel@...ux.ibm.com>
>> ---
>>   arch/s390/kvm/kvm-s390.c | 1 +
>>   include/uapi/linux/kvm.h | 1 +
>>   2 files changed, 2 insertions(+)
>> 
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index b655a7d82bf0..8c695ee79612 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -568,6 +568,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>>   	case KVM_CAP_S390_VCPU_RESETS:
>>   	case KVM_CAP_SET_GUEST_DEBUG:
>>   	case KVM_CAP_S390_DIAG318:
>> +	case KVM_CAP_S390_CPU_TOPOLOGY:
>>   		r = 1;
>>   		break;
>>   	case KVM_CAP_SET_GUEST_DEBUG2:
>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>> index d9e4aabcb31a..081ce0cd44b9 100644
>> --- a/include/uapi/linux/kvm.h
>> +++ b/include/uapi/linux/kvm.h
>> @@ -1112,6 +1112,7 @@ struct kvm_ppc_resize_hpt {
>>   #define KVM_CAP_BINARY_STATS_FD 203
>>   #define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
>>   #define KVM_CAP_ARM_MTE 205
>> +#define KVM_CAP_S390_CPU_TOPOLOGY 206
>>   
>>   #ifdef KVM_CAP_IRQ_ROUTING
>>   
>> 

Regardless of what we end up with: we need documentation for any new cap
:)