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

Collin Walling
2020-06-19T15:47:50Z

On 6/19/20 10:52 AM, David Hildenbrand wrote:
> 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.
>

I thought shadow/unshadow was a load/store (respectively) when executing
in SIE for a level 3+ guest (where LPAR is level 1)?

* Shadow SCB (load shadow VSIE page; originally CPNC is 0)

* Execute diag318 (under SIE)

* Unshadow SCB (store in original VSIE page; CPNC is whatever code the
guest decided to set)

Don't we need to preserve the CPNC for the level 3+ guest somehow?

--
Regards,
Collin

Stay safe and stay healthy