Messages in this thread | | | Subject | Re: [PATCH v3 2/3] s390x: KVM: Implementation of Multiprocessor Topology-Change-Report | From | Christian Borntraeger <> | Date | Wed, 8 Sep 2021 15:16:50 +0200 |
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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.
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