On Thu, 22 Feb 2018 14:29:09 -0500 Matthew Rosato <mjros...@linux.vnet.ibm.com> wrote:
> On 02/22/2018 06:13 AM, Christian Borntraeger wrote: > > > > > > On 02/21/2018 06:39 PM, Cornelia Huck wrote: > >> 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?) > > > > We have different sclp facilities for attach/detach and information, so > > we can implement that. > > > > > >>> > >>> 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? > > > > Yes, go with this patch. Right now Linux guests will not make use of that, > > so > > we can re-add that if it turns out to be useful for future guests. > > > > > > > > Matt, last chance to complain with reasons why we want to keep the current > > standby memory > > solution in its current form. (Or please ack the patch if you agree) > > Nope, this makes sense given its incompatibility w/ the common layer. I > also agree with the prior comment that, should we revisit this feature > in the future, it should probably be via an s390-specific interface. > > Acked-by: Matthew Rosato <mjros...@linux.vnet.ibm.com> Thanks, applied (with the discussed description tweak) to s390-next. We should also mention this in the changelog once this hits master. I'll try to remember to do that.
