Re: [PATCH v2 8/8] KVM: s390: Fix KVM_S390_VCPU_FAULT ioctl

[Janosch Frank <frankja@linux.ibm.com>]

On 3/23/26 12:10, Steffen Eiden wrote:
> On Fri, Mar 20, 2026 at 05:15:42PM +0100, Claudio Imbrenda wrote:
>> A previous commit changed the behaviour of the KVM_S390_VCPU_FAULT
>> ioctl. The current (wrong) implementation will trigger a guest
>> addressing exception if the requested address lies outside of a
>> memslot, unless the VM is UCONTROL.
>>
>> Restore the previous behaviour by open coding the fault-in logic.
>>
>> Fixes: 3762e905ec2e ("KVM: s390: use __kvm_faultin_pfn()")
>> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> 
> Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
> 
> But I have a comment on a changed logic. And a nit
> 
>> ---
>>   arch/s390/kvm/kvm-s390.c | 18 +++++++++++++++---
>>   1 file changed, 15 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index ebcb0ef8835e..62f04931b54d 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -5520,9 +5520,21 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
>>   	}
>>   #endif
>>   	case KVM_S390_VCPU_FAULT: {
>> -		idx = srcu_read_lock(&vcpu->kvm->srcu);
>> -		r = vcpu_dat_fault_handler(vcpu, arg, 0);
> 	in here every vcpu_ucontrol_translate error (incl ENONEMs from
> 	kvm_s390_mmu_cache_topup) is converted into EREMOTE ...
>> -		srcu_read_unlock(&vcpu->kvm->srcu, idx);
>> +		gpa_t gaddr = arg;
>> +
>> +		scoped_guard(srcu, &vcpu->kvm->srcu) {
>> +			r = vcpu_ucontrol_translate(vcpu, &gaddr);
>> +			if (r)
>> +				break;
> 	... which is not longer the case here. As you explicitly convert
> 	ENOMENS in gmap_ucas_translate before the topup call tnot converting
> 	might be an overlook (in the topup function?).

Yeah, I second that.