Messages in this thread | | | Date | Fri, 18 Feb 2022 19:24:33 +0100 | Subject | Re: [PATCH v7 1/1] s390x: KVM: guest support for topology function | From | Pierre Morel <> |
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On 2/18/22 18:27, Pierre Morel wrote: > > > On 2/18/22 15:28, Janosch Frank wrote: >> On 2/18/22 14:13, Pierre Morel wrote: >>> >>> >>> On 2/17/22 18:17, Nico Boehr wrote: >>>> On Thu, 2022-02-17 at 10:59 +0100, Pierre Morel wrote: >>>> [...] >>>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c >>>>> index 2296b1ff1e02..af7ea8488fa2 100644 >>>>> --- a/arch/s390/kvm/kvm-s390.c >>>>> +++ b/arch/s390/kvm/kvm-s390.c >>>> [...] >> >> Why is there no interface to clear the SCA_UTILITY_MTCR on a subsystem >> reset? > > Right, I had one in my first version based on interception but I forgot > to implement an equivalent for KVM as I modified the implementation for > interpretation. > I will add this. > >> >> >>>>> -void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) >>>>> +/** >>>>> + * kvm_s390_vcpu_set_mtcr >>>>> + * @vcp: the virtual CPU >>>>> + * >>>>> + * Is only relevant if the topology facility is present. >>>>> + * >>>>> + * Updates the Multiprocessor Topology-Change-Report to signal >>>>> + * the guest with a topology change. >>>>> + */ >>>>> +static void kvm_s390_vcpu_set_mtcr(struct kvm_vcpu *vcpu) >>>>> { >>>>> + struct esca_block *esca = vcpu->kvm->arch.sca; >>>> >>>> utility is at the same offset for the bsca and the esca, still >>>> wondering whether it is a good idea to assume esca here... >>> >>> We can take bsca to be coherent with the include file where we define >>> ESCA_UTILITY_MTCR inside the bsca. >>> And we can rename the define to SCA_UTILITY_MTCR as it is common for >>> both BSCA and ESCA the (E) is too much. >> >> Yes and maybe add a comment that it's at the same offset for esca so >> there won't come up further questions in the future. > > OK > >> >>> >>>> >>>> [...] >>>>> diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h >>>>> index 098831e815e6..af04ffbfd587 100644 >>>>> --- a/arch/s390/kvm/kvm-s390.h >>>>> +++ b/arch/s390/kvm/kvm-s390.h >>>>> @@ -503,4 +503,29 @@ void kvm_s390_vcpu_crypto_reset_all(struct kvm >>>>> *kvm); >>>>> */ >>>>> extern unsigned int diag9c_forwarding_hz; >>>>> +#define S390_KVM_TOPOLOGY_NEW_CPU -1 >>>>> +/** >>>>> + * kvm_s390_topology_changed >>>>> + * @vcpu: the virtual CPU >>>>> + * >>>>> + * If the topology facility is present, checks if the CPU toplogy >>>>> + * viewed by the guest changed due to load balancing or CPU hotplug. >>>>> + */ >>>>> +static inline bool kvm_s390_topology_changed(struct kvm_vcpu *vcpu) >>>>> +{ >>>>> + if (!test_kvm_facility(vcpu->kvm, 11)) >>>>> + return false; >>>>> + >>>>> + /* A new vCPU has been hotplugged */ >>>>> + if (vcpu->arch.prev_cpu == S390_KVM_TOPOLOGY_NEW_CPU) >>>>> + return true; >>>>> + >>>>> + /* The real CPU backing up the vCPU moved to another socket >>>>> */ >>>>> + if (topology_physical_package_id(vcpu->cpu) != >>>>> + topology_physical_package_id(vcpu->arch.prev_cpu)) >>>>> + return true; >>>> >>>> Why is it OK to look just at the physical package ID here? What if the >>>> vcpu for example moves to a different book, which has a core with the >>>> same physical package ID? >> >> I'll need to look up stsi 15* output to understand this. >> But the architecture states that any change to the stsi 15 output sets >> the change bit so I'd guess Nico is correct. >> > > Yes, Nico is correct, as I already answered, however it is not any > change of stsi(15) but a change of stsi(15.1.2) output which sets the > change bit.
hum, that is what the POP says but in fact you are right a change of topology that changes the output of any STSI(15) sets the topology change report bit as the output of STSI(15.1.2) would be changed too obviously.
Regards, Pierre
-- Pierre Morel IBM Lab Boeblingen
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