Messages in this thread | | | Subject | Re: [PATCH v3 2/3] s390x: KVM: Implementation of Multiprocessor Topology-Change-Report | From | Pierre Morel <> | Date | Tue, 7 Sep 2021 14:28:22 +0200 |
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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...
-- Pierre Morel IBM Lab Boeblingen
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