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

[Janosch Frank]

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@xxxxxxxxxxxxx>
>
> Reviewed-by: Steffen Eiden <seiden@xxxxxxxxxxxxx>
>
> 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.