On 14/05/2020 19.20, Collin Walling wrote:
> On 5/14/20 5:53 AM, David Hildenbrand wrote:
>> On 14.05.20 11:49, Janosch Frank wrote:
>>> 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@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);
>
> Errr.. thought I dropped this message. We favored just using the
> VM_EVENT from last time.
>
>>>>>>> +
>>>>>>> + 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?
>
> Pardon my ignorance, but I do not think I fully understand what exactly
> should be dropped in favor of doing things in userspace.
>
> My assumption: if a diag handler is not found in KVM, then we
> fallthrough to userspace handling?
Right, if you simply omit this change to diag.c, the default case
returns -EOPNOTSUPP which then should cause an exit to userspace. You
can then add the code in QEMU to handle_diag() in target/s390x/kvm.c
instead.
Thomas
