Re: [PATCH] KVM: s390: Remove false WARN_ON_ONCE for the PQAP instruction

David Hildenbrand
2020-05-05T08:29:00Z

On 05.05.20 10:27, Christian Borntraeger wrote:
>
>
> On 05.05.20 10:04, David Hildenbrand wrote:
>> On 05.05.20 09:55, Christian Borntraeger wrote:
>>>
>>>
>>> On 05.05.20 09:53, Cornelia Huck wrote:
>>>> On Tue, 5 May 2020 09:35:25 +0200
>>>> Christian Borntraeger <borntraeger@de.ibm.com> wrote:
>>>>
>>>>> In LPAR we will only get an intercept for FC==3 for the PQAP
>>>>> instruction. Running nested under z/VM can result in other intercepts as
>>>>> well, for example PQAP(QCI). So the WARN_ON_ONCE is not right. Let
>>>>> us simply remove it.
>>>>
>>>> While I agree with removing the WARN_ON_ONCE, I'm wondering why z/VM
>>>> gives us intercepts for those fcs... is that just a result of nesting
>>>> (or the z/VM implementation), or is there anything we might want to do?
>>>
>>> Yes nesting.
>>> The ECA bit for interpretion is an effective one. So if the ECA bit is off
>>> in z/VM (no crypto cards) our ECA bit is basically ignored as these bits
>>> are ANDed.
>>> I asked Tony to ask the z/VM team if that is the case here.
>>>
>>
>> So we can't detect if we have support for ECA_APIE, because there is no
>> explicit feature bit, right? Rings a bell. Still an ugly
>> hardware/firmware specification.
>
> Yes, no matter if this is the case here, we cannot rely on ECA_APIE to not
> trigger intercepts. So we must remove the WARN_ON.
>
> cc stable?

Yes, I'd say so.

--
Thanks,

David / dhildenb