Messages in this thread | | | Subject | Re: [PATCH v4 1/7] s390: ap: kvm: add PQAP interception for AQIC | From | Pierre Morel <> | Date | Thu, 28 Feb 2019 14:16:09 +0100 |
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On 28/02/2019 12:22, Cornelia Huck wrote: > On Thu, 28 Feb 2019 12:03:38 +0100 > Christian Borntraeger <borntraeger@de.ibm.com> wrote: > >> On 28.02.2019 10:42, Christian Borntraeger wrote: >> [...] >>>> Okay, let's go back to the genesis of this discussion; namely, my >>>> suggestion about moving the fc == 0x03 check into the hook code. If >>>> the vfio_ap module is not loaded, there will be no hook code. In that >>>> case, the check for the hook will fail and ultimately response code >>>> 0x01 will be set in the status word (which may not be the right thing >>>> to do?). You have not stated a single good reason for keeping this >>>> check, but I'm done with this silly argument. It certainly doesn't >>>> hurt anything. >>> >>> The instruction handler must handle the basic checks for the >>> instruction itself as outlined above. >>> >>> Do we want to allow QEMU to fully emulate everything (the ECA_APIE case being off)? >>> The we should pass along everything to QEMU, but this is already done with the >>> ECA_APIE check, correct? >>> >>> Do we agree that when we are beyond the ECA_APIE check, that we do not emulate >>> in QEMU and we have enabled the AP instructions interpretion? >>> If yes then this has some implication: >>> >>> 1. ECA is on and we should only get PQAP interception for specific FC (namely 3). >>> 2. What we certainly should check is the facility bit of the guest (65) and reject fc==3 >>> right away with a specification exception. I do not want the hook to mess with >>> the kvm cpu model. @Pierre would be good to actually check test_kvm_facility(vcpu->kvm, 65)) >>> 3. What shall we do when fc == 0x3? We can certainly do the check here OR in the >>> hook. As long as we have only fc==3 this does not matter. >>> >>> Correct? >> >> Thinking more about that, I think we should inject a specification exception for all >> unknown FCc != 0x3. That would also qualify for keeping it in the instruction handler. >> > > So, to summarize, the function should do: > - Is userspace supposed to emulate everything (!ECA_APIE)? Return > -EOPNOTSUPP to hand control to it. > - We are now interpreting the instruction in KVM. Do common checks > (PSTATE etc.) and inject exceptions, if needed. > - Now look at the fc; if there's a handler for it, call that; if not > (case does not attempt to call a specific handler, or no handler > registered), inject a specification exception. (Do we want pre-checks > like for facility 65 here, or in the handler?) > > That response code 0x01 thingy probably needs to go into the specific > handler function, if anywhere (don't know the semantics, sorry).
What do you mean with specific handler function?
If you mean a switch around the FC with static function's call, I agree, if you mean a jump into a hook I do not agree.
> > Question: Will the handlers for the individual fcs need to generate > different exceptions on their own? I.e., do they need to do injections > themselves, or should the calling function possibly inject an exception > on error?
There are some specificities.
> > (Are there more possible fcs than 0x3 and whatever the other > subfunction was?) >
Yes, at least 5 different FC are implemented in the Linux kernel today AFAIK.
Regards, Pierre
-- Pierre Morel Linux/KVM/QEMU in Böblingen - Germany
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