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

[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 vsie code does, that seems
to make sense.

So we don't need to shadow OR unshadow the CPNC, then?

-- 
Regards,
Collin

Stay safe and stay healthy