On Tue, 20 Feb 2018 16:05:54 +0100 David Hildenbrand <da...@redhat.com> wrote:
> On 20.02.2018 15:57, Cornelia Huck wrote: > > On Tue, 20 Feb 2018 13:16:37 +0100 > > David Hildenbrand <da...@redhat.com> wrote: > > > >> On 20.02.2018 13:05, Christian Borntraeger wrote: > >>> > >>> > >>> On 02/19/2018 06:42 PM, David Hildenbrand wrote: > >>>> From an architecture point of view, nothing can be mapped into the > >>>> address > >>>> space on s390x. All there is is memory. Therefore there is also not > >>>> really > >>>> an interface to communicate such information to the guest. All we can do > >>>> is > >>>> specify the maximum ram address and guests can probe in that range if > >>>> memory is available and usable (TPROT). > >>> > >>> In fact there is an interface in SCLP that describes the memory sizes > >>> (maximum in > >>> read scp info) and the details (read_storage_element0_info). I am asking > >>> myself > >>> if we should re-introduce read_storage_element_info and use that to avoid > >>> tprot > >> > >> Yes, we could do that (basically V1 of this patch) but have to glue it > >> to the a compatibility machine then. > > > > Actually, this makes quite a bit of sense (introduce the interface for > > everyone in 2.12 and turn it off in compat machines). > > Jup, either 2.12 or 2.13, no need to hurry. > > > > > Does real hardware have configurations where you can get the memory > > sizes, but not the attach/deattach support? (Hardware with the feature, > > but no standby memory defined?) > > I would guess that "0" for standby memory is valid but only people with > access to documentation can answer that :) So, should we go with this patch now and re-introduce the read functions if the above is indeed true? > > >> Interesting, didn't know about that. Will rephrase then to > >> > >> "While the hypervisor can deny to online an increment, all increments > >> have to be predefined and there is no way of telling the guest about a > >> newly "hotplugged" increment." > > > > Rephrase which part? :) > > "And nobody can really hinder it from doing so." OK.
