Re: [PATCH v8 2/2] s390/kvm: diagnose 0x318 sync and reset

David Hildenbrand
2020-06-19T14:53:06Z

On 19.06.20 00:22, Collin Walling wrote:
> DIAGNOSE 0x318 (diag318) sets information regarding the environment
> the VM is running in (Linux, z/VM, etc) and is observed via
> firmware/service events.
>
> This is a privileged s390x instruction that must be intercepted by
> SIE. Userspace handles the instruction as well as migration. Data
> is communicated via VCPU register synchronization.
>
> The Control Program Name Code (CPNC) is stored in the SIE block. The
> CPNC along with the Control Program Version Code (CPVC) are stored
> in the kvm_vcpu_arch struct.
>
> The CPNC is shadowed/unshadowed in VSIE.
>

[...]

>
> int kvm_arch_vcpu_ioctl_set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
> @@ -4194,6 +4198,10 @@ static void sync_regs_fmt2(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
> if (vcpu->arch.pfault_token == KVM_S390_PFAULT_TOKEN_INVALID)
> kvm_clear_async_pf_completion_queue(vcpu);
> }
> + if (kvm_run->kvm_dirty_regs & KVM_SYNC_DIAG318) {
> + vcpu->arch.diag318_info.val = kvm_run->s.regs.diag318;
> + vcpu->arch.sie_block->cpnc = vcpu->arch.diag318_info.cpnc;
> + }
> /*
> * If userspace sets the riccb (e.g. after migration) to a valid state,
> * we should enable RI here instead of doing the lazy enablement.
> @@ -4295,6 +4303,7 @@ static void store_regs_fmt2(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
> kvm_run->s.regs.pp = vcpu->arch.sie_block->pp;
> kvm_run->s.regs.gbea = vcpu->arch.sie_block->gbea;
> kvm_run->s.regs.bpbc = (vcpu->arch.sie_block->fpf & FPF_BPBC) == FPF_BPBC;
> + kvm_run->s.regs.diag318 = vcpu->arch.diag318_info.val;
> if (MACHINE_HAS_GS) {
> __ctl_set_bit(2, 4);
> if (vcpu->arch.gs_enabled)
> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
> index 9e9056cebfcf..ba83d0568bc7 100644
> --- a/arch/s390/kvm/vsie.c
> +++ b/arch/s390/kvm/vsie.c
> @@ -423,6 +423,8 @@ static void unshadow_scb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
> break;
> }
>
> + scb_o->cpnc = scb_s->cpnc;

"This is a privileged s390x instruction that must be intercepted", how
can the cpnc change, then, while in SIE?

Apart from that LGTM.

--
Thanks,

David / dhildenb