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

David Hildenbrand
2020-06-19T18:13:15Z

> Am 19.06.2020 um 19:56 schrieb Collin Walling <walling@linux.ibm.com>:
>
> ﻿On 6/19/20 1:17 PM, David Hildenbrand wrote:
>>> On 19.06.20 17:47, Collin Walling wrote:
>>> 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)
>>
>> 1. Here, you copy the cpnc from the pinned (original) SCB to the shadow SCB.
>>
>>>
>>> * Execute diag318 (under SIE)
>>
>> 2. Here the SIE runs using the shadow SCB.
>>
>>>
>>> * Unshadow SCB (store in original VSIE page; CPNC is whatever code the
>>> guest decided to set)
>>
>> 3. Here you copy back the cpnc from the shadow SCB to the pinned
>> (original) SCB.
>>
>>
>> If 2. cannot modify the cpnc residing in the shadow SCB, 3. can be
>> dropped, because the values will always match.
>>
>>
>> If guest3 tries to modify the cpnc (via diag 318), we exit the SIE
>> (intercept) in 2., return to our guest 2. guest 2 will perform the
>> change and adapt the original SCB.
>>
>> (yep, it's confusing)
>>
>> Or did I miss anything?
>>
>
> Ah, I see. So the shadowing isn't necessarily for SIE block values, but
> for storing the register / PSW / clock states, as well as facility bits
> for the level 3+ guests? Looking at what the

We have to forward all values the SIE has to see and copy back only what could have been changed by the SIE.

> vsie code does, that seems
> to make sense.
>
> So we don't need to shadow OR unshadow the CPNC, then?

I think you have to shadow (forward the value) but not unshadow (value cannot change).

Cheers!

>
> --
> Regards,
> Collin
>
> Stay safe and stay healthy
>