Re: [PATCH v2] KVM: s390: provide a capability for AIS state migration

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On 09.11.2017 10:53, Cornelia Huck wrote:
> On Thu,  9 Nov 2017 10:47:23 +0100
> Christian Borntraeger <borntraeger@xxxxxxxxxx> wrote:
> 
>> The AIS capability was introduced in 4.12, while the interface to
>> migrate the state was added in 4.13. Unfortunately it is not possible
>> for userspace to detect the migration capability without creating a flic
>> kvm device. As in QEMU the the cpu model detection runs on the "none"
> 
> s/the the/the/
> 
>> machine this will result in cpu model issues regarding the "ais"
>> capability.
>>
>> To get the "ais" capability properly let's add a new KVM capability that
>> tells userspace that AIS states can be migrated.
>>
>> Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
>> ---
>>  Documentation/virtual/kvm/api.txt               | 8 ++++++++
>>  Documentation/virtual/kvm/devices/s390_flic.txt | 2 ++
>>  arch/s390/kvm/kvm-s390.c                        | 1 +
>>  include/uapi/linux/kvm.h                        | 1 +
>>  4 files changed, 12 insertions(+)
>>
>> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
>> index e63a35f..51553ba 100644
>> --- a/Documentation/virtual/kvm/api.txt
>> +++ b/Documentation/virtual/kvm/api.txt
>> @@ -4347,3 +4347,11 @@ This capability indicates that userspace can load HV_X64_MSR_VP_INDEX msr.  Its
>>  value is used to denote the target vcpu for a SynIC interrupt.  For
>>  compatibilty, KVM initializes this msr to KVM's internal vcpu index.  When this
>>  capability is absent, userspace can still query this msr's value.
>> +
>> +8.13 KVM_CAP_S390_AIS_MIGRATION
>> +
>> +Architectures: s390
>> +Parameters: none
>> +
>> +This capability indicates if the flic device will be able to get/set the
>> +AIS states for migration via the KVM_DEV_FLIC_AISM_ALL attribute.
> 
> "and allows to discover this without having to create a flic device."
> 
>> diff --git a/Documentation/virtual/kvm/devices/s390_flic.txt b/Documentation/virtual/kvm/devices/s390_flic.txt
>> index 27ad53c..a4e20a0 100644
>> --- a/Documentation/virtual/kvm/devices/s390_flic.txt
>> +++ b/Documentation/virtual/kvm/devices/s390_flic.txt
>> @@ -151,6 +151,8 @@ struct kvm_s390_ais_all {
>>      to an ISC (MSB0 bit 0 to ISC 0 and so on). The combination of simm bit and
>>      nimm bit presents AIS mode for a ISC.
>>  
>> +    KVM_DEV_FLIC_AISM_ALL is indicated by KVM_CAP_S390_AIS_MIGRATION.
>> +
>>  Note: The KVM_SET_DEVICE_ATTR/KVM_GET_DEVICE_ATTR device ioctls executed on
>>  FLIC with an unknown group or attribute gives the error code EINVAL (instead of
>>  ENXIO, as specified in the API documentation). It is not possible to conclude
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index de6a5b7..8f4b655 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -395,6 +395,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>>  	case KVM_CAP_S390_USER_INSTR0:
>>  	case KVM_CAP_S390_CMMA_MIGRATION:
>>  	case KVM_CAP_S390_AIS:
>> +	case KVM_CAP_S390_AIS_MIGRATION:
>>  		r = 1;
>>  		break;
>>  	case KVM_CAP_S390_MEM_OP:
>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>> index 8388875..b605956 100644
>> --- a/include/uapi/linux/kvm.h
>> +++ b/include/uapi/linux/kvm.h
>> @@ -930,6 +930,7 @@ struct kvm_ppc_resize_hpt {
>>  #define KVM_CAP_PPC_SMT_POSSIBLE 147
>>  #define KVM_CAP_HYPERV_SYNIC2 148
>>  #define KVM_CAP_HYPERV_VP_INDEX 149
>> +#define KVM_CAP_S390_AIS_MIGRATION 150
>>  
>>  #ifdef KVM_CAP_IRQ_ROUTING
>>  
> 
> With the small addition above,
> 
> Reviewed-by: Cornelia Huck <cohuck@xxxxxxxxxx>
> 

Looks good to me and avoids trouble we had in qemu.

Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>

-- 

Thanks,

David / dhildenb
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