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

Christian Borntraeger
2020-05-05T08:27:23Z

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?

>
> Seems to be the right thing to do
>
> Reviewed-by: David Hildenbrand <david@redhat.com>
>