Re: [PATCH] s390x: pv: Fix diag318 PV fencing

[Janosch Frank <frankja@linux.ibm.com>]

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On 10/22/20 10:32 AM, David Hildenbrand wrote:
> On 22.10.20 10:23, Janosch Frank wrote:
>> Diag318 fencing needs to be determined on the current VM PV state and
>> not on the state that the VM has when we create the CPU model.
>>
>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>> Reported-by: Marc Hartmayer <mhartmay@linux.ibm.com>
>> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
>> Fixes: fabdada935 ("s390: guest support for diagnose 0x318")
>> ---
>>
>> If you're sure that this is what you want, then I'll send a v2 of the
>> patch set.
> 
> So that's going to be the first CPU feature that gets suppressed in PC
> mode - which seems to be what we want.
> 
> diag318_needed() will return false, resulting in vmstate_diag318() not
> being included in the migration stream (I know, we don't support
> migration yet for PV).

Well either you have it and need to migrate it or you don't.
As it doesn't persist over IPLs, that should not be a problem, no?

> 
> I don't see where diag318 would get reset during a reipl - is it
> expected to be persistent when switching in/out of PV, or when reipling
> etc..?

That's actually another bug we need to address. Diag318 will need to be
reset on a diag308 reset instead of when doing the cpu resets...

> 
>>
>> ---
>>  target/s390x/cpu_features.c | 5 +++++
>>  target/s390x/cpu_features.h | 4 ++++
>>  target/s390x/cpu_models.c   | 4 ++++
>>  target/s390x/kvm.c          | 3 +--
>>  4 files changed, 14 insertions(+), 2 deletions(-)
>>
>> diff --git a/target/s390x/cpu_features.c b/target/s390x/cpu_features.c
>> index 31ea8df246..42fe0bf4ca 100644
>> --- a/target/s390x/cpu_features.c
>> +++ b/target/s390x/cpu_features.c
>> @@ -14,6 +14,7 @@
>>  #include "qemu/osdep.h"
>>  #include "qemu/module.h"
>>  #include "cpu_features.h"
>> +#include "hw/s390x/pv.h"
>>  
>>  #define DEF_FEAT(_FEAT, _NAME, _TYPE, _BIT, _DESC) \
>>      [S390_FEAT_##_FEAT] = {                        \
>> @@ -105,6 +106,10 @@ void s390_fill_feat_block(const S390FeatBitmap features, S390FeatType type,
>>          }
>>          feat = find_next_bit(features, S390_FEAT_MAX, feat + 1);
>>      }
>> +
>> +    if (type == S390_FEAT_TYPE_SCLP_FAC134 && s390_is_pv()) {
>> +        clear_be_bit(s390_feat_def(S390_FEAT_DIAG_318)->bit, data);
>> +    }
>>  }
>>  
>>  void s390_add_from_feat_block(S390FeatBitmap features, S390FeatType type,
>> diff --git a/target/s390x/cpu_features.h b/target/s390x/cpu_features.h
>> index ef52ffce83..87463f064d 100644
>> --- a/target/s390x/cpu_features.h
>> +++ b/target/s390x/cpu_features.h
>> @@ -81,6 +81,10 @@ const S390FeatGroupDef *s390_feat_group_def(S390FeatGroup group);
>>  
>>  #define BE_BIT_NR(BIT) (BIT ^ (BITS_PER_LONG - 1))
>>  
>> +static inline void clear_be_bit(unsigned int bit_nr, uint8_t *array)
>> +{
>> +    array[bit_nr / 8] &= ~(0x80 >> (bit_nr % 8));
>> +}
>>  static inline void set_be_bit(unsigned int bit_nr, uint8_t *array)
>>  {
>>      array[bit_nr / 8] |= 0x80 >> (bit_nr % 8);
>> diff --git a/target/s390x/cpu_models.c b/target/s390x/cpu_models.c
>> index ca484bfda7..461e0b8f4a 100644
>> --- a/target/s390x/cpu_models.c
>> +++ b/target/s390x/cpu_models.c
>> @@ -29,6 +29,7 @@
>>  #include "hw/pci/pci.h"
>>  #endif
>>  #include "qapi/qapi-commands-machine-target.h"
>> +#include "hw/s390x/pv.h"
>>  
>>  #define CPUDEF_INIT(_type, _gen, _ec_ga, _mha_pow, _hmfai, _name, _desc) \
>>      {                                                                    \
>> @@ -238,6 +239,9 @@ bool s390_has_feat(S390Feat feat)
>>          }
>>          return 0;
>>      }
>> +    if (feat == S390_FEAT_DIAG_318 && s390_is_pv()) {
>> +        return false;
>> +    }
>>      return test_bit(feat, cpu->model->features);
>>  }
>>  
>> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
>> index f13eff688c..baa070fdf7 100644
>> --- a/target/s390x/kvm.c
>> +++ b/target/s390x/kvm.c
>> @@ -2498,8 +2498,7 @@ void kvm_s390_get_host_cpu_model(S390CPUModel *model, Error **errp)
>>       */
>>      set_bit(S390_FEAT_EXTENDED_LENGTH_SCCB, model->features);
>>  
>> -    /* DIAGNOSE 0x318 is not supported under protected virtualization */
>> -    if (!s390_is_pv() && kvm_check_extension(kvm_state, KVM_CAP_S390_DIAG318)) {
>> +    if (kvm_check_extension(kvm_state, KVM_CAP_S390_DIAG318)) {
>>          set_bit(S390_FEAT_DIAG_318, model->features);
>>      }
>>  
>>
> 
> 



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