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 14:47:39 +0200 |
| |
On 23/08/2018 13:12, David Hildenbrand wrote: > On 23.08.2018 13:10, Pierre Morel wrote: >> On 23/08/2018 12:28, David Hildenbrand wrote: >>> On 23.08.2018 12:00, Halil Pasic wrote: >>>> >>>> >>>> On 08/23/2018 09:44 AM, David Hildenbrand wrote: >>>>> On 22.08.2018 22:16, Tony Krowiak wrote: >>>>>> On 08/22/2018 07:24 AM, David Hildenbrand wrote: >>>>>>> On 22.08.2018 13:19, David Hildenbrand wrote: >>>>>>>> On 13.08.2018 23:48, Tony Krowiak wrote: >>>>>>>>> From: Tony Krowiak <akrowiak@linux.ibm.com> >>>>>>>>> >>>>>>>>> Introduces a new CPU model feature and two CPU model >>>>>>>>> facilities to support AP virtualization for KVM guests. >>>>>>>>> >>>>>>>>> CPU model feature: >>>>>>>>> >>>>>>>>> The KVM_S390_VM_CPU_FEAT_AP feature indicates that >>>>>>>>> AP instructions are available on the guest. This >>>>>>>>> feature will be enabled by the kernel only if the AP >>>>>>>>> instructions are installed on the linux host. This feature >>>>>>>>> must be specifically turned on for the KVM guest from >>>>>>>>> userspace to use the VFIO AP device driver for guest >>>>>>>>> access to AP devices. >>>>>>>>> >>>>>>>>> CPU model facilities: >>>>>>>>> >>>>>>>>> 1. AP Query Configuration Information (QCI) facility is installed. >>>>>>>>> >>>>>>>>> This is indicated by setting facilities bit 12 for >>>>>>>>> the guest. The kernel will not enable this facility >>>>>>>>> for the guest if it is not set on the host. >>>>>>>>> >>>>>>>>> If this facility is not set for the KVM guest, then only >>>>>>>>> APQNs with an APQI less than 16 will be used by a Linux >>>>>>>>> guest regardless of the matrix configuration for the virtual >>>>>>>>> machine. This is a limitation of the Linux AP bus. >>>>>>>>> >>>>>>>>> 2. AP Facilities Test facility (APFT) is installed. >>>>>>>>> >>>>>>>>> This is indicated by setting facilities bit 15 for >>>>>>>>> the guest. The kernel will not enable this facility for >>>>>>>>> the guest if it is not set on the host. >>>>>>>>> >>>>>>>>> If this facility is not set for the KVM guest, then no >>>>>>>>> AP devices will be available to the guest regardless of >>>>>>>>> the guest's matrix configuration for the virtual >>>>>>>>> machine. This is a limitation of the Linux AP bus. >>>>>>>>> >>>>>>>>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com> >>>>>>>>> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com> >>>>>>>>> Reviewed-by: Halil Pasic <pasic@linux.ibm.com> >>>>>>>>> Tested-by: Michael Mueller <mimu@linux.ibm.com> >>>>>>>>> Tested-by: Farhan Ali <alifm@linux.ibm.com> >>>>>>>>> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com> >>>>>>>>> --- >>>>>>>>> arch/s390/kvm/kvm-s390.c | 5 +++++ >>>>>>>>> arch/s390/tools/gen_facilities.c | 2 ++ >>>>>>>>> 2 files changed, 7 insertions(+), 0 deletions(-) >>>>>>>>> >>>>>>>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c >>>>>>>>> index 1e8cb67..d5e04d2 100644 >>>>>>>>> --- a/arch/s390/kvm/kvm-s390.c >>>>>>>>> +++ b/arch/s390/kvm/kvm-s390.c >>>>>>>>> @@ -367,6 +367,11 @@ static void kvm_s390_cpu_feat_init(void) >>>>>>>>> >>>>>>>>> if (MACHINE_HAS_ESOP) >>>>>>>>> allow_cpu_feat(KVM_S390_VM_CPU_FEAT_ESOP); >>>>>>>>> + >>>>>>>>> + /* Check if AP instructions installed on host */ >>>>>>>>> + if (ap_instructions_available()) >>>>>>>>> + allow_cpu_feat(KVM_S390_VM_CPU_FEAT_AP); >>>>>>>>> + >>>>>>>>> /* >>>>>>>>> * We need SIE support, ESOP (PROT_READ protection for gmap_shadow), >>>>>>>>> * 64bit SCAO (SCA passthrough) and IDTE (for gmap_shadow unshadowing). >>>>>>>>> diff --git a/arch/s390/tools/gen_facilities.c b/arch/s390/tools/gen_facilities.c >>>>>>>>> index 90a8c9e..a52290b 100644 >>>>>>>>> --- a/arch/s390/tools/gen_facilities.c >>>>>>>>> +++ b/arch/s390/tools/gen_facilities.c >>>>>>>>> @@ -106,6 +106,8 @@ struct facility_def { >>>>>>>>> >>>>>>>>> .name = "FACILITIES_KVM_CPUMODEL", >>>>>>>>> .bits = (int[]){ >>>>>>>>> + 12, /* AP Query Configuration Information */ >>>>>>>>> + 15, /* AP Facilities Test */ >>>>>>>>> -1 /* END */ >>>>>>>>> } >>>>>>>>> }, >>>>>>>>> >>>>>>>> I really wonder if we should also export the APXA facility. >>>>>>>> >>>>>>>> We can probe and allow that CPU feature. However, we cannot disable it >>>>>>>> (as of now). >>>>>>>> >>>>>>>> We have other CPU features where it is the same case (basically all >>>>>>>> subfunctions). See kvm_s390_get_processor_subfunc(). We probe them and >>>>>>>> export them, but support to disable them has never been implemented. >>>>>>>> >>>>>>>> On a high level, we could then e.g. deny to start a QEMU guest if APXA >>>>>>>> is available but has been disabled. (until we know that disabling it >>>>>>>> actually works - if ever). >>>>>>>> >>>>>>>> This helps to catch nasty migration bugs (e.g. APXA suddenly >>>>>>>> disappearing). Although unlikely, definitely possible. >>>>>>>> >>>>>>>> >>>>>>>> Are there any other AP related facilities that the guest can from now on >>>>>>>> probe that should also become part of the CPU model? >>>>>>>> >>>>>>> To be more precise, shouldn't PQAP(QCI) be handled just like other >>>>>>> subfunctions? (I remember it should) >>>>>> >>>>>> When you suggest PQAP(QCI) be handled like other subfunctions, are you >>>>>> suggesting that there should be a field in struct kvm_s390_vm_cpu_subfunc >>>>>> with a bit indicating the QCI subfunction is available? The availability >>>>>> of the QCI subfunction of the PQAP instruction is determined by facilities >>>>>> bit 12. Is it not enough to export facilities bit 12? >>>>> >>>>> The feature block (128 bit) from PQAP(QCI) should be passed through a >>>>> subfunction block to QEMU. >>>>> >>>> >>>> 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. >>> >> >> David, >> I already answered to you on this subject. >> >> First, >> Are you sure you do not mistake QCI for TAPQ which has the t bit >> instruction interception bit as all the instructions you use as >> subfunctions? > > Yes, I am pretty sure it is PQAP(QCI), please check with Christian / > architecture documentations.
OK.
> >> >> Second, >> The TAPQ interception bit is exposed through the facility bit 15 >> and is documented as being installed when the APXA facility is installed. >> >> If we have the APFT, we have the APXA, problem seems solved to me.
hum. wrong, sorry, the assertion is in the wrong way...
> > What is apsc, qact, rc8a in the qci blocks? are the facility bits?
Yes, facility bits concerning the AP instructions
> >> >> Regards, >> Pierre >> > >
-- Pierre Morel Linux/KVM/QEMU in Böblingen - Germany
| |