On 14.05.20 10:52, Janosch Frank wrote:
> On 5/14/20 9:53 AM, Thomas Huth wrote:
>> On 14/05/2020 00.15, Collin Walling wrote:
>>> DIAGNOSE 0x318 (diag318) is a privileged s390x instruction that must
>>> be intercepted by SIE and handled via KVM. Let's introduce some
>>> functions to communicate between userspace and KVM via ioctls. These
>>> will be used to get/set the diag318 related information, as well as
>>> check the system if KVM supports handling this instruction.
>>>
>>> This information can help with diagnosing the environment the VM is
>>> running in (Linux, z/VM, etc) if the OS calls this instruction.
>>>
>>> By default, this feature is disabled and can only be enabled if a
>>> user space program (such as QEMU) explicitly requests it.
>>>
>>> The Control Program Name Code (CPNC) is stored in the SIE block
>>> and a copy is retained in each VCPU. The Control Program Version
>>> Code (CPVC) is not designed to be stored in the SIE block, so we
>>> retain a copy in each VCPU next to the CPNC.
>>>
>>> Signed-off-by: Collin Walling <walling@xxxxxxxxxxxxx>
>>> ---
>>> Documentation/virt/kvm/devices/vm.rst | 29 +++++++++
>>> arch/s390/include/asm/kvm_host.h | 6 +-
>>> arch/s390/include/uapi/asm/kvm.h | 5 ++
>>> arch/s390/kvm/diag.c | 20 ++++++
>>> arch/s390/kvm/kvm-s390.c | 89 +++++++++++++++++++++++++++
>>> arch/s390/kvm/kvm-s390.h | 1 +
>>> arch/s390/kvm/vsie.c | 2 +
>>> 7 files changed, 151 insertions(+), 1 deletion(-)
>> [...]
>>> diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c
>>> index 563429dece03..3caed4b880c8 100644
>>> --- a/arch/s390/kvm/diag.c
>>> +++ b/arch/s390/kvm/diag.c
>>> @@ -253,6 +253,24 @@ static int __diag_virtio_hypercall(struct kvm_vcpu *vcpu)
>>> return ret < 0 ? ret : 0;
>>> }
>>>
>>> +static int __diag_set_diag318_info(struct kvm_vcpu *vcpu)
>>> +{
>>> + unsigned int reg = (vcpu->arch.sie_block->ipa & 0xf0) >> 4;
>>> + u64 info = vcpu->run->s.regs.gprs[reg];
>>> +
>>> + if (!vcpu->kvm->arch.use_diag318)
>>> + return -EOPNOTSUPP;
>>> +
>>> + vcpu->stat.diagnose_318++;
>>> + kvm_s390_set_diag318_info(vcpu->kvm, info);
>>> +
>>> + VCPU_EVENT(vcpu, 3, "diag 0x318 cpnc: 0x%x cpvc: 0x%llx",
>>> + vcpu->kvm->arch.diag318_info.cpnc,
>>> + (u64)vcpu->kvm->arch.diag318_info.cpvc);
>>> +
>>> + return 0;
>>> +}
>>> +
>>> int kvm_s390_handle_diag(struct kvm_vcpu *vcpu)
>>> {
>>> int code = kvm_s390_get_base_disp_rs(vcpu, NULL) & 0xffff;
>>> @@ -272,6 +290,8 @@ int kvm_s390_handle_diag(struct kvm_vcpu *vcpu)
>>> return __diag_page_ref_service(vcpu);
>>> case 0x308:
>>> return __diag_ipl_functions(vcpu);
>>> + case 0x318:
>>> + return __diag_set_diag318_info(vcpu);
>>> case 0x500:
>>> return __diag_virtio_hypercall(vcpu);
>>
>> I wonder whether it would make more sense to simply drop to userspace
>> and handle the diag 318 call there? That way the userspace would always
>> be up-to-date, and as we've seen in the past (e.g. with the various SIGP
>> handling), it's better if the userspace is in control... e.g. userspace
>> could also decide to only use KVM_S390_VM_MISC_ENABLE_DIAG318 if the
>> guest just executed the diag 318 instruction.
>>
>> And you need the kvm_s390_vm_get/set_misc functions anyway, so these
>> could also be simply used by the diag 318 handler in userspace?
>>
>>> default:
>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>>> index d05bb040fd42..c3eee468815f 100644
>>> --- a/arch/s390/kvm/kvm-s390.c
>>> +++ b/arch/s390/kvm/kvm-s390.c
>>> @@ -159,6 +159,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
>>> { "diag_9c_ignored", VCPU_STAT(diagnose_9c_ignored) },
>>> { "instruction_diag_258", VCPU_STAT(diagnose_258) },
>>> { "instruction_diag_308", VCPU_STAT(diagnose_308) },
>>> + { "instruction_diag_318", VCPU_STAT(diagnose_318) },
>>> { "instruction_diag_500", VCPU_STAT(diagnose_500) },
>>> { "instruction_diag_other", VCPU_STAT(diagnose_other) },
>>> { NULL }
>>> @@ -1243,6 +1244,76 @@ static int kvm_s390_get_tod(struct kvm *kvm, struct kvm_device_attr *attr)
>>> return ret;
>>> }
>>>
>>> +void kvm_s390_set_diag318_info(struct kvm *kvm, u64 info)
>>> +{
>>> + struct kvm_vcpu *vcpu;
>>> + int i;
>>> +
>>> + kvm->arch.diag318_info.val = info;
>>> +
>>> + VM_EVENT(kvm, 3, "SET: CPNC: 0x%x CPVC: 0x%llx",
>>> + kvm->arch.diag318_info.cpnc, kvm->arch.diag318_info.cpvc);
>>> +
>>> + if (sclp.has_diag318) {
>>> + kvm_for_each_vcpu(i, vcpu, kvm) {
>>> + vcpu->arch.sie_block->cpnc = kvm->arch.diag318_info.cpnc;
>>> + }
>>> + }
>>> +}
>>> +
>>> +static int kvm_s390_vm_set_misc(struct kvm *kvm, struct kvm_device_attr *attr)
>>> +{
>>> + int ret;
>>> + u64 diag318_info;
>>> +
>>> + switch (attr->attr) {
>>> + case KVM_S390_VM_MISC_ENABLE_DIAG318:
>>> + kvm->arch.use_diag318 = 1;
>>> + ret = 0;
>>> + break;
>>
>> Would it make sense to set kvm->arch.use_diag318 = 1 during the first
>> execution of KVM_S390_VM_MISC_DIAG318 instead, so that we could get
>> along without the KVM_S390_VM_MISC_ENABLE_DIAG318 ?
>
> I'm not an expert in feature negotiation, but why isn't this a cpu
> feature like sief2 instead of a attribute?
>
> @David?
In the end you want to have it somehow in the CPU model I guess. You
cannot glue it to QEMU machines, because availability depends on HW+KVM
support.
How does the guest detect that it can use diag318? I assume/hope via a a
STFLE feature.
--
Thanks,
David / dhildenb
