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

David Hildenbrand
2020-05-05T08:04:44Z

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.

Seems to be the right thing to do

Reviewed-by: David Hildenbrand <david@redhat.com>

--
Thanks,

David / dhildenb