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?

> 
>> +	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
>