Messages in this thread | | | Subject | Re: [PATCH v5 1/7] s390: ap: kvm: add PQAP interception for AQIC | From | Pierre Morel <> | Date | Tue, 19 Mar 2019 18:07:07 +0100 |
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On 19/03/2019 15:54, Halil Pasic wrote: > On Tue, 19 Mar 2019 11:01:44 +0100 > Pierre Morel <pmorel@linux.ibm.com> wrote: > >> On 15/03/2019 18:28, Halil Pasic wrote: > > [..] > >>> >>> Things get complicated when one considers that ECA.28 is an effective >>> control. >> >> I don't think so, ECA_28 is not really a problem. >> We do not propagate ECA_AIV in VSIE and ECA_AIV is tested in the vfio >> driver to support GISA. >> So that the guest 3 will not support interrupt. >> > > That was not my concern, but while we are at it... I guess you refer to > the check in handle_pqap(). That seems to do -EOPNOTSUPP, i.e. got to > userspace, i.e. with today's QEMU operation exception. Which does not > seem right.
We already discussed this. no?
> > My concern was the following. Let assume > ECA.28 == 1 and EECA.28 == 0 != 1 > and guest issues a PQAP (for simplicity AQIC). > > Currently I guess we take a 0x04 interception and go to userspace, which > may or may not be the best thing to do. > > With this patch we would take a 0x04, but (opposed to before) if guest > does not have facility 65 we go with a specification exception.
This is not right. We return -EOPNOTSUPP which will be intercepted by QEMU which will report an OPERATION exception as before.
> Operation exception should however take priority over this kind of > specification exception. So basically everything except PQAP/AQIC would > give you and operation exception (with current QEMU), but PQAP/AQIC would > give you a specification exception. Which is wrong! > > AFAICT there is no way to tell if we got a 04 interception because > EECA.28 != 1 (and ECA.28 == 1) and FW won't interpret the AP > instructions for us, or because it PQAP/AQIC is a mandatory intercept. > In other words I don't see a way to tell if EECA.28 is 1 when > interpreting PQAP/AQIC. > > Do you agree?
No. EECA = HOST_ECA & GUEST_ECA after we made sure that AP instructions are available, HOST_ECA=1
(vcpu->arch.sie_block->eca & ECA_APIE) gives us the answer.
In the case HOST_ECA=0 we always go to userland as before.
> > [..] > >> >> Yes, the alternative is: >> >> 1) We do things right but this mean we change the ABI (SPECIFICATION >> instead of OPERATION) >> >> I thing this is the best thing to do, it is the implementation >> proposed by this patch where all is done in Kernel, so that we are >> right what ever the userland user is (QEMU or other). >> >> 2) We want to preserve the old ABI for old QEMU >> Then I proposed the implementation here under. >> >> >> My personal opinion, is that we should change the ABI and do things >> right now. > > I tend to agree. Giving an operation exception instead of a specification > exception is a bug. If it is a kernel or qemu bug it ain't clear to me > at the moment. > >> We should also do it right for TAPQ with t bit set. I remember >> Christian already warned about this but we did not implement it. >> > > Yes, I have some blurry memories of something similar myself. I wonder > if there was a reason, or did we just forget to address this issue.
I will integrate it in the next iteration too, even it is not IRQ, the PQAP hook patch can be more general.
Regards, Pierre
> > Regards, > Halil >
-- Pierre Morel Linux/KVM/QEMU in Böblingen - Germany
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