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 ?
> + 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?
Thomas
