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?
>
>> + case KVM_S390_VM_MISC_DIAG318:
>> + ret = -EFAULT;
>> + if (!kvm->arch.use_diag318)
>> + return -EOPNOTSUPP;
>> + if (get_user(diag318_info, (u64 __user *)attr->addr))
>> + break;
>> + kvm_s390_set_diag318_info(kvm, diag318_info);
>> + ret = 0;
>> + break;
>> + default:
>> + ret = -ENXIO;
>> + break;
>> + }
>> + return ret;
>> +}
>
> What about a reset of the guest VM? If a user first boots into a Linux
> kernel that supports diag 318, then reboots and selects a Linux kernel
> that does not support diag 318? I'd expect that the cpnc / cpnv values
> need to be cleared here somewhere? Otherwise the information might not
> be accurate anymore?
He resets via QEMU on a machine reset.
>
> Thomas
>
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