Messages in this thread | | | Subject | Re: [PATCH v3 2/3] s390x: KVM: Implementation of Multiprocessor Topology-Change-Report | From | Pierre Morel <> | Date | Wed, 8 Sep 2021 16:17:22 +0200 |
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On 9/8/21 3:16 PM, Christian Borntraeger wrote: > > > On 08.09.21 15:09, Pierre Morel wrote: >> >> >> On 9/8/21 9:07 AM, Christian Borntraeger wrote: >>> >>> >>> On 07.09.21 14:28, Pierre Morel wrote: >>>> >>>> >>>> On 9/6/21 8:37 PM, David Hildenbrand wrote: >>>>> On 03.08.21 10:26, Pierre Morel wrote: >>>>>> We let the userland hypervisor know if the machine support the CPU >>>>>> topology facility using a new KVM capability: >>>>>> KVM_CAP_S390_CPU_TOPOLOGY. >>>>>> >>>>>> The PTF instruction will report a topology change if there is any >>>>>> change >>>>>> with a previous STSI_15_2 SYSIB. >>>>>> Changes inside a STSI_15_2 SYSIB occur if CPU bits are set or clear >>>>>> inside the CPU Topology List Entry CPU mask field, which happens with >>>>>> changes in CPU polarization, dedication, CPU types and adding or >>>>>> removing CPUs in a socket. >>>>>> >>>>>> The reporting to the guest is done using the Multiprocessor >>>>>> Topology-Change-Report (MTCR) bit of the utility entry of the guest's >>>>>> SCA which will be cleared during the interpretation of PTF. >>>>>> >>>>>> To check if the topology has been modified we use a new field of the >>>>>> arch vCPU to save the previous real CPU ID at the end of a schedule >>>>>> and verify on next schedule that the CPU used is in the same socket. >>>>>> >>>>>> We deliberatly ignore: >>>>>> - polarization: only horizontal polarization is currently used in >>>>>> linux. >>>>>> - CPU Type: only IFL Type are supported in Linux >>>>>> - Dedication: we consider that only a complete dedicated CPU stack >>>>>> can >>>>>> take benefit of the CPU Topology. >>>>>> >>>>>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com> >>>>> >>>>> >>>>>> @@ -228,7 +232,7 @@ struct kvm_s390_sie_block { >>>>>> __u8 icptcode; /* 0x0050 */ >>>>>> __u8 icptstatus; /* 0x0051 */ >>>>>> __u16 ihcpu; /* 0x0052 */ >>>>>> - __u8 reserved54; /* 0x0054 */ >>>>>> + __u8 mtcr; /* 0x0054 */ >>>>>> #define IICTL_CODE_NONE 0x00 >>>>>> #define IICTL_CODE_MCHK 0x01 >>>>>> #define IICTL_CODE_EXT 0x02 >>>>>> @@ -246,6 +250,7 @@ struct kvm_s390_sie_block { >>>>>> #define ECB_TE 0x10 >>>>>> #define ECB_SRSI 0x04 >>>>>> #define ECB_HOSTPROTINT 0x02 >>>>>> +#define ECB_PTF 0x01 >>>>> >>>>> From below I understand, that ECB_PTF can be used with stfl(11) in >>>>> the hypervisor. >>>>> >>>>> What is to happen if the hypervisor doesn't support stfl(11) and we >>>>> consequently cannot use ECB_PTF? Will QEMU be able to emulate PTF >>>>> fully? >>>>> >>>>> >>>>>> __u8 ecb; /* 0x0061 */ >>>>>> #define ECB2_CMMA 0x80 >>>>>> #define ECB2_IEP 0x20 >>>>>> @@ -747,6 +752,7 @@ struct kvm_vcpu_arch { >>>>>> bool skey_enabled; >>>>>> struct kvm_s390_pv_vcpu pv; >>>>>> union diag318_info diag318_info; >>>>>> + int prev_cpu; >>>>>> }; >>>>>> struct kvm_vm_stat { >>>>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c >>>>>> index b655a7d82bf0..ff6d8a2b511c 100644 >>>>>> --- a/arch/s390/kvm/kvm-s390.c >>>>>> +++ b/arch/s390/kvm/kvm-s390.c >>>>>> @@ -568,6 +568,7 @@ int kvm_vm_ioctl_check_extension(struct kvm >>>>>> *kvm, long ext) >>>>>> case KVM_CAP_S390_VCPU_RESETS: >>>>>> case KVM_CAP_SET_GUEST_DEBUG: >>>>>> case KVM_CAP_S390_DIAG318: >>>>>> + case KVM_CAP_S390_CPU_TOPOLOGY: >>>>> >>>>> I would have expected instead >>>>> >>>>> r = test_facility(11); >>>>> break >>>>> >>>>> ... >>>>> >>>>>> r = 1; >>>>>> break; >>>>>> case KVM_CAP_SET_GUEST_DEBUG2: >>>>>> @@ -819,6 +820,23 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, >>>>>> struct kvm_enable_cap *cap) >>>>>> icpt_operexc_on_all_vcpus(kvm); >>>>>> r = 0; >>>>>> break; >>>>>> + case KVM_CAP_S390_CPU_TOPOLOGY: >>>>>> + mutex_lock(&kvm->lock); >>>>>> + if (kvm->created_vcpus) { >>>>>> + r = -EBUSY; >>>>>> + } else { >>>>> >>>>> ... >>>>> } else if (test_facility(11)) { >>>>> set_kvm_facility(kvm->arch.model.fac_mask, 11); >>>>> set_kvm_facility(kvm->arch.model.fac_list, 11); >>>>> r = 0; >>>>> } else { >>>>> r = -EINVAL; >>>>> } >>>>> >>>>> similar to how we handle KVM_CAP_S390_VECTOR_REGISTERS. >>>>> >>>>> But I assume you want to be able to support hosts without ECB_PTF, >>>>> correct? >>>>> >>>>> >>>>>> + set_kvm_facility(kvm->arch.model.fac_mask, 11); >>>>>> + set_kvm_facility(kvm->arch.model.fac_list, 11); >>>>>> + r = 0; >>>>>> + } >>>>>> + mutex_unlock(&kvm->lock); >>>>>> + VM_EVENT(kvm, 3, "ENABLE: CPU TOPOLOGY %s", >>>>>> + r ? "(not available)" : "(success)"); >>>>>> + break; >>>>>> + >>>>>> + r = -EINVAL; >>>>>> + break; >>>>> >>>>> ^ dead code >>>>> >>>>> [...] >>>>> >>>>>> } >>>>>> void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) >>>>>> { >>>>>> + vcpu->arch.prev_cpu = vcpu->cpu; >>>>>> vcpu->cpu = -1; >>>>>> if (vcpu->arch.cputm_enabled && !is_vcpu_idle(vcpu)) >>>>>> __stop_cpu_timer_accounting(vcpu); >>>>>> @@ -3198,6 +3239,11 @@ static int kvm_s390_vcpu_setup(struct >>>>>> kvm_vcpu *vcpu) >>>>>> vcpu->arch.sie_block->ecb |= ECB_HOSTPROTINT; >>>>>> if (test_kvm_facility(vcpu->kvm, 9)) >>>>>> vcpu->arch.sie_block->ecb |= ECB_SRSI; >>>>>> + >>>>>> + /* PTF needs both host and guest facilities to enable >>>>>> interpretation */ >>>>>> + if (test_kvm_facility(vcpu->kvm, 11) && test_facility(11)) >>>>>> + vcpu->arch.sie_block->ecb |= ECB_PTF; >>>>> >>>>> Here you say we need both ... >>>>> >>>>>> + >>>>>> if (test_kvm_facility(vcpu->kvm, 73)) >>>>>> vcpu->arch.sie_block->ecb |= ECB_TE; >>>>>> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c >>>>>> index 4002a24bc43a..50d67190bf65 100644 >>>>>> --- a/arch/s390/kvm/vsie.c >>>>>> +++ b/arch/s390/kvm/vsie.c >>>>>> @@ -503,6 +503,9 @@ static int shadow_scb(struct kvm_vcpu *vcpu, >>>>>> struct vsie_page *vsie_page) >>>>>> /* Host-protection-interruption introduced with ESOP */ >>>>>> if (test_kvm_cpu_feat(vcpu->kvm, KVM_S390_VM_CPU_FEAT_ESOP)) >>>>>> scb_s->ecb |= scb_o->ecb & ECB_HOSTPROTINT; >>>>>> + /* CPU Topology */ >>>>>> + if (test_kvm_facility(vcpu->kvm, 11)) >>>>>> + scb_s->ecb |= scb_o->ecb & ECB_PTF; >>>>> >>>>> but here you don't check? >>>>> >>>>>> /* transactional execution */ >>>>>> if (test_kvm_facility(vcpu->kvm, 73) && wants_tx) { >>>>>> /* remap the prefix is tx is toggled on */ >>>>>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h >>>>>> index d9e4aabcb31a..081ce0cd44b9 100644 >>>>>> --- a/include/uapi/linux/kvm.h >>>>>> +++ b/include/uapi/linux/kvm.h >>>>>> @@ -1112,6 +1112,7 @@ struct kvm_ppc_resize_hpt { >>>>>> #define KVM_CAP_BINARY_STATS_FD 203 >>>>>> #define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204 >>>>>> #define KVM_CAP_ARM_MTE 205 >>>>>> +#define KVM_CAP_S390_CPU_TOPOLOGY 206 >>>>> >>>>> We'll need a Documentation/virt/kvm/api.rst description. >>>>> >>>>> I'm not completely confident that the way we're handling the >>>>> capability+facility is the right approach. It all feels a bit >>>>> suboptimal. >>>>> >>>>> Except stfl(74) -- STHYI --, we never enable a facility via >>>>> set_kvm_facility() that's not available in the host. And STHYI is >>>>> special such that it is never implemented in hardware. >>>>> >>>>> I'll think about what might be cleaner once I get some more details >>>>> about the interaction with stfl(11) in the hypervisor. >>>>> >>>> >>>> OK, may be we do not need to handle the case stfl(11) is not present >>>> in the host, these are pre GA10... >>> >>> What about VSIE? For all existing KVM guests, stfl11 is off. >> >> In VSIE the patch activates stfl(11) only if the host has stfl(11). >> >> I do not see any problem to activate the interpretation in VSIE with >> ECB_PTF (ECB.7) when the host has stfl(11) and QEMU asks to enable it >> for the guest using the CAPABILITY as it is done in this patch. >> >> if any intermediary hypervizor decide to not advertize stfl(11) for >> the guest like an old QEMU not having the CAPABILITY, or a QEMU with >> ctop=off, KVM will not set ECB_PTF and the PTF instruction will >> trigger a program check as before. >> >> Is it OK or did I missed something? > > Yes, sure. > My point was regarding the pre z10 statement. We will see hosts without > stfl(e)11 when running nested on z14, z15 and co.
Ah OK, yes. understood.
Thanks, Pierre
-- Pierre Morel IBM Lab Boeblingen
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