Re: [PATCH v2 2/3] s390/vfio-ap: set status response code to 06 on gisc registration failure

[Tony Krowiak]

On 10/27/23 10:03, Halil Pasic wrote:
> On Fri, 27 Oct 2023 09:36:26 -0400
> Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
>
> > > > The interception handler for the PQAP(AQIC) command calls the
> > > > kvm_s390_gisc_register function to register the guest ISC with the channel
> > > > subsystem. If that call fails, the status response code 08 - indicating
> > > > Invalid ZONE/GISA designation - is returned to the guest. This response
> > > > code does not make sense because the non-zero return code from the
> > > > kvm_s390_gisc_register function can be due one of two things: Either the
> > > > ISC passed as a parameter by the guest to the PQAP(AQIC) command is greater
> > > > than the maximum ISC value allowed, or the guest is not using a GISA.
> > >
> > > The "ISC passed as a parameter by the guest to the PQAP(AQIC) command is
> > > greater than the maximum ISC value allowed" is not possible. The isc is
> > > 3 bits wide and all 8 values that can be represented on 3 bits are valid.
> > >
> > > This is only possible if the hypervisor was to mess up, or if the machine
> > > was broken.
> >
> > kvm_s390_gisc_register(struct kvm *kvm, u32 gisc)
> > {
> > 	struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;
> >
> > 	if (!gi->origin)
> > 		return -ENODEV;
> > 	if (gisc > MAX_ISC)
> > 		return -ERANGE;
> > ...
> >
> > Just quoting what is in the code.
>
> Right! But it is not the guest that calls this function directly. This
> function is called by the vfio_ap code.
>
> The guest passes ISC in bits 61, 62 and 63 of GR1.
>
> So the guest can't give you an invalid value.

Yes, I got it the first time you said that.

> Regards,
> Halil