Messages in this thread Patch in this message | | | From | David Hildenbrand <> | Subject | Re: [PATCH v3 2/3] s390x: KVM: Implementation of Multiprocessor Topology-Change-Report | Date | Mon, 6 Sep 2021 20:37:35 +0200 |
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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.
-- Thanks, David / dhildenb
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