Re: [PATCH v2 1/2] target/s390x/kvm: Turn KVM_CAP_SYNC_REGS into a hard requirement

[Thomas Huth <thuth@redhat.com>]

On 10/10/2023 13.02, Christian Borntraeger wrote:
> 
> 
> Am 09.10.23 um 19:07 schrieb Thomas Huth:
>> Since we already require at least kernel 3.15 in the s390x KVM code,
>> we can assume that the KVM_CAP_SYNC_REGS capability is always there.
>> Thus turn this into a hard requirement now.
>>
>> Signed-off-by: Thomas Huth <thuth@redhat.com>
>> ---
>>   target/s390x/kvm/kvm.c | 20 ++++++++++++++------
>>   1 file changed, 14 insertions(+), 6 deletions(-)
>>
>> diff --git a/target/s390x/kvm/kvm.c b/target/s390x/kvm/kvm.c
>> index bc5c56a305..b3e2eaa2eb 100644
>> --- a/target/s390x/kvm/kvm.c
>> +++ b/target/s390x/kvm/kvm.c
>> @@ -337,21 +337,29 @@ int kvm_arch_get_default_type(MachineState *ms)
>>   int kvm_arch_init(MachineState *ms, KVMState *s)
>>   {
>> +    int required_caps[] = {
>> +        KVM_CAP_DEVICE_CTRL,
>> +        KVM_CAP_SYNC_REGS,
>> +    };
>> +
>> +    for (int i = 0; i < ARRAY_SIZE(required_caps); i++) {
>> +        if (!kvm_check_extension(s, required_caps[i])) {
>> +            error_report("KVM is missing capability #%d - "
>> +                         "please use kernel 3.15 or newer", 
>> required_caps[i]);
>> +            return -1;
>> +        }
>> +    }
>> +
>>       object_class_foreach(ccw_machine_class_foreach, TYPE_S390_CCW_MACHINE,
>>                            false, NULL);
>> -    if (!kvm_check_extension(kvm_state, KVM_CAP_DEVICE_CTRL)) {
>> -        error_report("KVM is missing capability KVM_CAP_DEVICE_CTRL - "
>> -                     "please use kernel 3.15 or newer");
>> -        return -1;
>> -    }
>>       if (!kvm_check_extension(s, KVM_CAP_S390_COW)) {
>>           error_report("KVM is missing capability KVM_CAP_S390_COW - "
>>                        "unsupported environment");
>>           return -1;
>>       }
> 
> Not sure if we also want to move KVM_CAP_S390_COW somehow. The message would 
> be different.

IIRC that error could happen when you ran KVM within an older version of 
z/VM, so the "please use kernel 3.15 or newer" message would be completely 
misleading there.

> Aparch from that:
> Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>

Thanks,
   Thomas