Messages in this thread | | | Date | Wed, 13 Jul 2022 11:01:35 +0200 | From | Janosch Frank <> | Subject | Re: [PATCH v12 3/3] KVM: s390: resetting the Topology-Change-Report |
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On 7/12/22 13:17, Pierre Morel wrote: > > > On 7/12/22 10:47, Janis Schoetterl-Glausch wrote: >> On 7/12/22 09:24, Pierre Morel wrote: >>> >>> >>> 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. >>> >> I agree, but I didn't suggest it for performance reasons. > > Yes, and that is why I do not agree ;) > >> I was thinking about future proofing, that is if the architecture is extended. >> We don't know if future extensions are best handled in the kernel or user space, >> so if we prevent it from going to user space, we can defer the decision to when we know more. > > If future extensions are better handle in kernel we will handle them in > kernel, obviously, in this case we will need a patch. > > If it is not better handle in kernel we will handle the extensions in > userland and we will not need a kernel patch making the update of the > virtual architecture easier and faster. > > If we prohibit the extensions in kernel we will need a kernel patch in > both cases and a userland patch if it is not completely handled in kernel. > > In userland we check any wrong selector before the instruction goes back > to the guest.
I opt for passing the lower selectors down for QEMU to handle.
> >> But that's only relevant if STSI can be extended without a capability, which is why I asked about that. > > Logicaly any change, extension, in the architecture should be signaled > by a facility bit or something. > >> >>> 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.
That's actually a good point.
New instruction interceptions for PV will need to be enabled by KVM via a switch somewhere since the UV can't rely on the fact that KVM will correctly handle it without an enablement.
So please remove the pv check
>>> >>> 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.
Yes
>>> >>>> >>>>> +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 >> >> Wait no, I didn't get how that works. You're passing the value via attr->attr, not reading it from addr. > > :) 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.
kvm_s390_set_topology_change_indication
It's long but it's rarely used. Maybe shorten topology to "topo"
[..] >>>> 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. >> You're right, it doesn't make a difference. >> What about doing put_user(topo, (u8 *)attr->addr)), seems more straight forward. > > OK
(u8 __user *)
Always go the explicit route if possible
> >>> >>>> >>>>> + return -EFAULT; >>>>> + >>>>> + return 0; >>>>> +} >>>>> + >>>> [...] >>>> >>> >> >
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