Re: [PATCH v5 2/2] s390/kvm: diagnose 318 handling

David Hildenbrand
2019-06-26T14:31:47Z

On 26.06.19 16:30, Collin Walling wrote:
> On 6/26/19 6:28 AM, Christian Borntraeger wrote:
>>
>>
>> On 26.06.19 11:45, David Hildenbrand wrote:
>>
>>>
>>> BTW. there is currently no mechanism to fake absence of diag318. Should
>>> we have one? (in contrast, for CMMA we have, which is also a CPU feature)
>>
>> Yes, we want to be able to disable diag318 via a CPU model feature. That actually
>> means that the kernel must not answer this if we disable it.
>>
> Correct. If the guest specifies diag318=off, then the instruction
> shouldn't be executed (it is fenced off in the kernel by checking the
> Read SCP Info bit).

But the guest *could* execute it and not get an exception.

--

Thanks,

David / dhildenb