Messages in this thread | | | Date | Tue, 12 Jul 2022 09:24:52 +0200 | Subject | Re: [PATCH v12 3/3] KVM: s390: resetting the Topology-Change-Report | From | Pierre Morel <> |
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On 7/11/22 15:22, Janis Schoetterl-Glausch wrote: > On 7/11/22 10:41, Pierre Morel wrote: >> During a subsystem reset the Topology-Change-Report is cleared. >> >> Let's give userland the possibility to clear the MTCR in the case >> of a subsystem reset. >> >> To migrate the MTCR, we give userland the possibility to >> query the MTCR state. >> >> We indicate KVM support for the CPU topology facility with a new >> KVM capability: KVM_CAP_S390_CPU_TOPOLOGY. >> >> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com> > > Reviewed-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com> >
Thanks!
> See nits/comments below. > >> --- >> Documentation/virt/kvm/api.rst | 25 ++++++++++++++ >> arch/s390/include/uapi/asm/kvm.h | 1 + >> arch/s390/kvm/kvm-s390.c | 56 ++++++++++++++++++++++++++++++++ >> include/uapi/linux/kvm.h | 1 + >> 4 files changed, 83 insertions(+) >> >> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst >> index 11e00a46c610..5e086125d8ad 100644 >> --- a/Documentation/virt/kvm/api.rst >> +++ b/Documentation/virt/kvm/api.rst >> @@ -7956,6 +7956,31 @@ should adjust CPUID leaf 0xA to reflect that the PMU is disabled. >> When enabled, KVM will exit to userspace with KVM_EXIT_SYSTEM_EVENT of >> type KVM_SYSTEM_EVENT_SUSPEND to process the guest suspend request. >> >> +8.37 KVM_CAP_S390_CPU_TOPOLOGY >> +------------------------------ >> + >> +:Capability: KVM_CAP_S390_CPU_TOPOLOGY >> +:Architectures: s390 >> +:Type: vm >> + >> +This capability indicates that KVM will provide the S390 CPU Topology >> +facility which consist of the interpretation of the PTF instruction for >> +the function code 2 along with interception and forwarding of both the >> +PTF instruction with function codes 0 or 1 and the STSI(15,1,x) > > Is the architecture allowed to extend STSI without a facility? > If so, if we say here that STSI 15.1.x is passed to user space, then > I think we should have a > > if (sel1 != 1) > goto out_no_data; > > or maybe even > > if (sel1 != 1 || sel2 < 2 || sel2 > 6) > goto out_no_data; > > in priv.c
I am not a big fan of doing everything in the kernel. Here we have no performance issue since it is an error of the guest if it sends a wrong selector.
Even testing the facility or PV in the kernel is for my opinion arguable in the case we do not do any treatment in the kernel.
I do not see what it brings to us, it increase the LOCs and makes the implementation less easy to evolve.
> >> +instruction to the userland hypervisor. >> + >> +The stfle facility 11, CPU Topology facility, should not be indicated >> +to the guest without this capability. >> + >> +When this capability is present, KVM provides a new attribute group >> +on vm fd, KVM_S390_VM_CPU_TOPOLOGY. >> +This new attribute allows to get, set or clear the Modified Change > > get or set, now that there is no explicit clear anymore.
Yes now it is a set to 0 but the action of clearing remains.
> >> +Topology Report (MTCR) bit of the SCA through the kvm_device_attr >> +structure.> + >> +When getting the Modified Change Topology Report value, the attr->addr > > When getting/setting the... > >> +must point to a byte where the value will be stored. > > ... will be stored/retrieved from.
OK
>> + >> 9. Known KVM API problems >> ========================= >> >> diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h >> index 7a6b14874d65..a73cf01a1606 100644 >> --- a/arch/s390/include/uapi/asm/kvm.h >> +++ b/arch/s390/include/uapi/asm/kvm.h >> @@ -74,6 +74,7 @@ struct kvm_s390_io_adapter_req { >> #define KVM_S390_VM_CRYPTO 2 >> #define KVM_S390_VM_CPU_MODEL 3 >> #define KVM_S390_VM_MIGRATION 4 >> +#define KVM_S390_VM_CPU_TOPOLOGY 5 >> >> /* kvm attributes for mem_ctrl */ >> #define KVM_S390_VM_MEM_ENABLE_CMMA 0 >> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c >> index 70436bfff53a..b18e0b940b26 100644 >> --- a/arch/s390/kvm/kvm-s390.c >> +++ b/arch/s390/kvm/kvm-s390.c >> @@ -606,6 +606,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) >> case KVM_CAP_S390_PROTECTED: >> r = is_prot_virt_host(); >> break; >> + case KVM_CAP_S390_CPU_TOPOLOGY: >> + r = test_facility(11); >> + break; >> default: >> r = 0; >> } >> @@ -817,6 +820,20 @@ 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: >> + r = -EINVAL; >> + mutex_lock(&kvm->lock); >> + if (kvm->created_vcpus) { >> + r = -EBUSY; >> + } 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; >> + } >> + mutex_unlock(&kvm->lock); >> + VM_EVENT(kvm, 3, "ENABLE: CAP_S390_CPU_TOPOLOGY %s", >> + r ? "(not available)" : "(success)"); >> + break; >> default: >> r = -EINVAL; >> break; >> @@ -1717,6 +1734,36 @@ static void kvm_s390_update_topology_change_report(struct kvm *kvm, bool val) >> read_unlock(&kvm->arch.sca_lock); >> } >> >> +static int kvm_s390_set_topology(struct kvm *kvm, struct kvm_device_attr *attr) > > kvm_s390_set_topology_changed maybe? > kvm_s390_get_topology_changed below then.
No strong opinion, if you prefer I change this.
> >> +{ >> + if (!test_kvm_facility(kvm, 11)) >> + return -ENXIO; >> + >> + kvm_s390_update_topology_change_report(kvm, !!attr->attr); >> + return 0; >> +} >> + >> +static int kvm_s390_get_topology(struct kvm *kvm, struct kvm_device_attr *attr) >> +{ >> + union sca_utility utility; >> + struct bsca_block *sca; >> + __u8 topo; >> + >> + if (!test_kvm_facility(kvm, 11)) >> + return -ENXIO; >> + >> + read_lock(&kvm->arch.sca_lock); >> + sca = kvm->arch.sca; >> + utility.val = READ_ONCE(sca->utility.val); > > I don't think you need the READ_ONCE anymore, now that there is a lock it should act as a compile barrier.
I think you are right.
>> + read_unlock(&kvm->arch.sca_lock); >> + topo = utility.mtcr; >> + >> + if (copy_to_user((void __user *)attr->addr, &topo, sizeof(topo))) > > Why void not u8?
I like to say we write on "topo" with the size of "topo". So we do not need to verify the effective size of topo. But I understand, it is a UAPI, setting u8 in the copy_to_user makes sense too. For my personal opinion, I would have prefer that userland tell us the size it awaits even here, for this special case, since we use a byte, we can not do really wrong.
> >> + return -EFAULT; >> + >> + return 0; >> +} >> + > [...] >
-- Pierre Morel IBM Lab Boeblingen
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