Re: [PATCH] target/s390x/kvm: Enable adapter interruption suppression again

[Thomas Huth <thuth@redhat.com>]

On 16/01/2020 13.23, David Hildenbrand wrote:
> On 16.01.20 13:20, Thomas Huth wrote:
>> The AIS feature has been disabled late in the v2.10 development
>> cycle since there were some issues with migration (see commit
>> 3f2d07b3b01ea61126b - "s390x/ais: for 2.10 stable: disable ais
>> facility"). We originally wanted to enable it again for newer
>> machine types, but apparently we forgot to do this so far. Let's
>> do it for the new s390-ccw-virtio-5.0 machine now.
>>
>> Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1756946
>> Signed-off-by: Thomas Huth <thuth@redhat.com>
>> ---
>>  hw/s390x/s390-virtio-ccw.c         |  4 ++++
>>  include/hw/s390x/s390-virtio-ccw.h |  4 ++++
>>  target/s390x/kvm.c                 | 11 ++++++++---
>>  3 files changed, 16 insertions(+), 3 deletions(-)
>>
>> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
>> index e7eadd14e8..6f43136396 100644
>> --- a/hw/s390x/s390-virtio-ccw.c
>> +++ b/hw/s390x/s390-virtio-ccw.c
>> @@ -456,6 +456,7 @@ static void ccw_machine_class_init(ObjectClass *oc, void *data)
>>      s390mc->cpu_model_allowed = true;
>>      s390mc->css_migration_enabled = true;
>>      s390mc->hpage_1m_allowed = true;
>> +    s390mc->kvm_ais_allowed = true;
>>      mc->init = ccw_init;
>>      mc->reset = s390_machine_reset;
>>      mc->hot_add_cpu = s390_hot_add_cpu;
>> @@ -662,6 +663,9 @@ static void ccw_machine_4_2_instance_options(MachineState *machine)
>>  
>>  static void ccw_machine_4_2_class_options(MachineClass *mc)
>>  {
>> +    S390CcwMachineClass *s390mc = S390_MACHINE_CLASS(mc);
>> +
>> +    s390mc->kvm_ais_allowed = false;
>>      ccw_machine_5_0_class_options(mc);
>>      compat_props_add(mc->compat_props, hw_compat_4_2, hw_compat_4_2_len);
>>  }
>> diff --git a/include/hw/s390x/s390-virtio-ccw.h b/include/hw/s390x/s390-virtio-ccw.h
>> index 8aa27199c9..f142d379c6 100644
>> --- a/include/hw/s390x/s390-virtio-ccw.h
>> +++ b/include/hw/s390x/s390-virtio-ccw.h
>> @@ -21,6 +21,9 @@
>>  #define S390_MACHINE_CLASS(klass) \
>>      OBJECT_CLASS_CHECK(S390CcwMachineClass, (klass), TYPE_S390_CCW_MACHINE)
>>  
>> +#define S390_CCW_MACHINE_OBJ_GET_CLASS(obj) \
>> +    OBJECT_GET_CLASS(S390CcwMachineClass, obj, TYPE_S390_CCW_MACHINE)
>> +
>>  typedef struct S390CcwMachineState {
>>      /*< private >*/
>>      MachineState parent_obj;
>> @@ -40,6 +43,7 @@ typedef struct S390CcwMachineClass {
>>      bool cpu_model_allowed;
>>      bool css_migration_enabled;
>>      bool hpage_1m_allowed;
>> +    bool kvm_ais_allowed;
>>  } S390CcwMachineClass;
>>  
>>  /* runtime-instrumentation allowed by the machine */
>> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
>> index 15260aeb9a..4c1c8c0208 100644
>> --- a/target/s390x/kvm.c
>> +++ b/target/s390x/kvm.c
>> @@ -329,6 +329,8 @@ static void ccw_machine_class_foreach(ObjectClass *oc, void *opaque)
>>  
>>  int kvm_arch_init(MachineState *ms, KVMState *s)
>>  {
>> +    S390CcwMachineClass *smc = S390_CCW_MACHINE_OBJ_GET_CLASS(ms);
>> +
>>      object_class_foreach(ccw_machine_class_foreach, TYPE_S390_CCW_MACHINE,
>>                           false, NULL);
>>  
>> @@ -365,10 +367,13 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>>      /*
>>       * The migration interface for ais was introduced with kernel 4.13
>>       * but the capability itself had been active since 4.12. As migration
>> -     * support is considered necessary let's disable ais in the 2.10
>> -     * machine.
>> +     * support is considered necessary we only enable this for newer
>> +     * machine types and if KVM_CAP_S390_AIS_MIGRATION is available.
>>       */
>> -    /* kvm_vm_enable_cap(s, KVM_CAP_S390_AIS, 0); */
>> +    if (smc->kvm_ais_allowed &&
>> +        kvm_check_extension(s, KVM_CAP_S390_AIS_MIGRATION)) {
>> +        kvm_vm_enable_cap(s, KVM_CAP_S390_AIS, 0);
>> +    }
>>  
>>      kvm_set_max_memslot_size(KVM_SLOT_MAX_BYTES);
>>      return 0;
>>
> 
> We have ri_allowed(), cpu_model_allowed(), hpage_1m_allowed().
> 
> Care to create a similar wrapper?

Honestly, why do we need these wrappers at all? They look cumbersome to
me. I'd rather remove them in case they are not urgently needed (so far
I don't see the point... could someone enlighten me why we have them?).

 Thomas