Messages in this thread | | | Subject | Re: [PATCH v9 21/22] KVM: s390: CPU model support for AP virtualization | From | Tony Krowiak <> | Date | Wed, 22 Aug 2018 17:05:31 -0400 |
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On 08/22/2018 12:57 PM, David Hildenbrand wrote: >>>> In this case we will have no problem with older guests not having idea >>>> about APXA. >>>> >>>> Would it be a solution? >>> Any feature the guest sees, should be part of the CPU model. The whole >>> environment for cpu subfunctions is already in place both in KVM and >>> QEMU. Only disabling subfunctions in KVM is not implemented yet. >>> >>> You can exclude any subfunctions/facilities that are only valid on LPAR >>> level and cannot be used in some guest either way. (that makes life >>> sometimes easier) >>> >>> >>> I know that this might sound a little bit complicated, but it really >>> isn't. Boils down to modifying kvm_s390_cpu_feat_init() and specifying >>> some features+feature groups in QEMU. >> OK, we definitively need another patch/patch-set, to handle this. >> Do you think it can be done in another series since if we always support >> APXA when we have AP instructions, we already have an indication that >> APXA exist: the AP facility. >> > Please implement the subfunction stuff right away. This will allow to > handle all future facilities transparently from a kernel POV.
I find your use of the term 'subfunction' confusing here. In the kvm_s390_cpu_feat_init(void) function, it looks like the kvm_s390_available_subfunc structure is filled in with bits returned from CPACF queries of various MSA facilities to indicate which CPACF functions are supported. APXA is not a subfunction but a facility that is indicated by a bit returned from the PQAP(QCI) instruction. If we are to implement this, wouldn't it be done as a CPU model feature as opposed to a subfunction? Am I misunderstanding what you are asking for?
> > Implementing that should be easy - and I don't like gluing features > together in such a way. > > You can always assure that consistent data (e.g. AP + APXA availability) > is reported from KVM to QEMU. > >> Regards, >> Pierre >> >> >> >> >
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