On Mon, 9 Apr 2018 12:37:42 +0200 Halil Pasic <pa...@linux.vnet.ibm.com> wrote:
> On 04/09/2018 11:32 AM, Cornelia Huck wrote: > >> We can kind of (i.e. modulo EECA.28) ensure this in a different fashion I > >> think. How > >> about proclaiming a 'has ap instructions, but nothing to see here' in the > >> SIE interpreted flavor (ECA.28 set) the default way of having ap > >> instructions > >> under KVM. This should be easily accomplished with an all zero CRYCB and > >> eca.28 > >> set. The for the guest to actually get real work done with AP we would > >> still require some sort of driver to either provide a non-zero matrix by > >> altering the CRYCB or unsettling ECA.28 and doing the intercepted flavor. > >> > >> Please notice, the cpu facility ap would still keep it's semantic > >> 'has ap instructions' (opposed to 'has ap instructions implemented in > >> SIE interpreted flavor). And give us all the flexibility. > >> > >> Yet implementing what we want to have in absence of a driver would become > >> much easier (under the assumption that ECA.28 equals EECA.28). > >> > >> How about this? > > Unfortunately, this is really hard to follow without the AR... let me > > summarize it to check whether I got the gist of it :) > > > > - If the "ap" cpu feature is specified, set a bit that indicates "hey, > > we basically have have AP support" and create the basics, but don't > > enable actual SIE handling. This means the guest gets exceptions from > > the SIE already and we don't need to emulate them. > > Kind of. The bit is ECA.28 and tells SIE 'hey SIE shall interpret ap > instructions for the guest (as specified)'. Then SIE has an SD satellite > called CRYCB that contains the which ap resources is the guest authorized > to use. These are the masks. If we set each mask to all zero, we will > effectively accomplish 'hey,we basically have have AP support but no > resources at the moment'. So, right, we don't have to emulate that. > > I don't know what do you mean by exceptions. For most legit requests the > SIE should say APQN invalid, with QCI being a notable exception. But > of course SIE would inject program exceptions (access, specification, > and privileged operation) accordingly I guess. I meant "emulate exceptions"... > > > In short, the SIE would do what we are trying to emulate in this patch. ...so yes, exactly that. > > > - Actually enable the missing pieces if a vfio device is created. This > > would enable processing by the SIE, and we would not need to do > > emulation, either (for most of it, IIRC). > > Yes. It would actually assign resources to the guest. That would enable > doing real work with the AP instructions. Ok. > > > > > I may be all wrong, though... can we at least have a translation of > > ECA.28 and EECA.28 (the "ap is there" bit and the "ap instructions are > > interpreted" bit?) > > > > I think we have a misunderstanding here. I will wait for Tony. Maybe > he can understand this better or explain in more accessible way. From what I get from your explanation, this approach sounds like a good way forward. But let's wait for Tony.
