On Tue, 19 Mar 2019 11:01:44 +0100 Pierre Morel <pmorel@xxxxxxxxxxxxx> 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. 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. 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? [..] > > 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. Regards, Halil
