Re: [PATCH v6 2/2] s390/kvm: diagnose 318 handling

[Janosch Frank <frankja@linux.ibm.com>]

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On 5/14/20 11:37 AM, David Hildenbrand wrote:
> 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@linux.ibm.com>
>>>> ---
>>>>  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.
> 
SCLP


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