Re: [PATCH RFCv3 6/9] s390x/diag: subcode to query device memory region

[Heiko Carstens]

On Mon, Jul 27, 2020 at 12:12:02PM +0200, David Hildenbrand wrote:
> >>>> +#define DIAG500_DEVICE_MEMORY_REGION   4  
> >>>
> >>> Regardless what we end up with, this needs to be specified
> >>> somewhere(tm).
> >>
> >> Yeah, there, we should also document the existing subcodes. What would
> >> be the right place for this? The kernel feels somewhat wrong to me.
> > 
> > The still supported subcode 3 is properly specified in the virtio spec.
> > That's not a good place for that new one, though.
> > 
> > QEMU is probably a better place than the kernel to specify stuff,
> > although it's not really ideal, either. OTOH, do we ever expect other
> > hypervisors to implement this new subcode?
> 
> cloud-hypervisor implements virtio-mem. If it were ever to support s390x
> (guess it does not yet), it would also want to implement that one. But
> then, it can just look at QEMU doc I guess :)

It must be well defined and easy to find also for kernel developers
who actually have to care about memory detection code :)