Messages in this thread | | | Subject | Re: [PATCH v9 21/22] KVM: s390: CPU model support for AP virtualization | From | Pierre Morel <> | Date | Thu, 23 Aug 2018 16:59:17 +0200 |
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On 23/08/2018 15:38, David Hildenbrand wrote: > On 23.08.2018 15:22, Halil Pasic wrote: >> >> >> On 08/23/2018 02:47 PM, Pierre Morel wrote: >>> On 23/08/2018 13:12, David Hildenbrand wrote: >> [..] >>>>>>> >>>>>>> I'm confused, which 128 bit? >>>>>> >>>>>> >>>>>> Me too :) , I was assuming this block to be 128bit, but the qci block >>>>>> has 128 bytes.... >>>>>> >>>>>> And looking at arch/s390/include/asm/ap.h, there is a lot of information >>>>>> contained that is definitely not of interest for CPU models... >>>>>> >>>>>> I wonder if there is somewhere defined which bits are reserved for >>>>>> future features/facilities, compared to ap masks and such. >>>>>> >>>>>> This is really hard to understand/plan without access to documentation. >>>>>> >>>>>> You (Halil, Tony, Pier, ...) should have a look if what I described >>>>>> related to PQAP(QCI) containing features that should get part of the CPU >>>>>> model makes sense or not. For now I was thinking that there is some part >>>>>> inside of QCI that is strictly reserved for facilities/features that we >>>>>> can use. >> >> No there is no such part. The architecture documentation is quite confusing >> with some aspects (e.g. persistence) of how exactly some of these features >> work and are indicated. I'm having a hard time finding my opinion. I may >> end up asking some questions later, but for now i have to think first. >> >> Just one hint. There is a programming note stating that if bit 2 of the >> QCI block is one there is at least one AP card in the machine that actually >> has APXA installed. >> >> I read the architecture so that the APXA has a 'cpu part' (if we are >> doing APXA the cpu can't spec exception on certain bits not being zor9) >> and a 'card(s) part'. >> >> Since the stuff seems quite difficult to sort out properly, I ask myself >> are there real problems we must solve? >> >> This ultimately seems to be about the migration, right? You say 'This helps >> to catch nasty migration bugs (e.g. APXA suddenly disappearing).' at the very >> beginning of the discussion. Yes, we don't have to have an vfio_ap device, >> he guest can and will start looking for AP resources if >> only the cpu model features installed. So the guest could observe >> a disappearing APXA, but I don't think that would lead to problems (with >> Linux at least). >> >> And there ain't much AP a guest can sanely do without if no AP resources >> are there. >> >> I would really prefer not rushing a solution if we don't have to. >> >>> >>> >>>> >>>> What is apsc, qact, rc8a in the qci blocks? are the facility bits? >>> >>> Yes, facility bits concerning the AP instructions >>> >> >> According to the current AR document rc8a ain't a facility but bits >> 0-2 and 4-7 kind of are. >> > > Easy ( :) ) answer. Everything that is the CPU part should get into the > CPU model. Everything that is AP specific not. If APXA is not a CPU > facility, fine with me to leave it out. > > Ack to not rushing, but also ack to not leaving out important things. > Ack that this stuff is hard to ficure out.
APXA is not a CPU part, it is a machine part (SIE) and a AP part (QCI,TAPQ), it has no influence on CPU instructions but on the AP instructions. Consequently, if I understood the definition correctly, it should not go in the CPU model.
Regards, Pierre
-- Pierre Morel Linux/KVM/QEMU in Böblingen - Germany
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