Re: [PATCH v3 1/1] vl/s390x: fixup ram sizes for compat machines

[Cornelia Huck <cohuck@redhat.com>]

On Wed,  1 Apr 2020 08:37:54 -0400
Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> Older QEMU versions did fixup the ram size to match what can be reported
> via sclp. We need to mimic this behaviour for machine types 4.2 and
> older to not fail on inbound migration for memory sizes that do not fit.
> Old machines with proper aligned memory sizes are not affected.
> 
> Alignment table:
>  VM size (<=) | Alignment
> --------------------------
>       1020M   |     1M
>       2040M   |     2M
>       4080M   |     4M
>       8160M   |     8M
>      16320M   |    16M
>      32640M   |    32M
>      65280M   |    64M
>     130560M   |   128M
>     261120M   |   256M
>     522240M   |   512M
>    1044480M   |     1G
>    2088960M   |     2G
>    4177920M   |     4G
>    8355840M   |     8G
> 
> Suggested action is to replace unaligned -m value with a suitable
> aligned one or if a change to a newer machine type is possible, use a
> machine version >= 5.0.
> 
> A future versions might remove the compatibility handling.

s/versions/version/ (fixed it up)

> 
> For machine types >= 5.0 we can simply use an increment size of 1M and
> use the full range of increment number which allows for all possible
> memory sizes. The old limitation of having a maximum of 1020 increments
> was added for standby memory, which we no longer support. With that we
> can now support even weird memory sizes like 10001234 MB.
> 
> As we no longer fixup maxram_size as well, make other users use ram_size
> instead. Keep using maxram_size when setting the maximum ram size in KVM,
> as that will come in handy in the future when supporting memory hotplug
> (in contrast, storage keys and storage attributes for hotplugged memory
> will have to be migrated per RAM block in the future).
> 
> Fixes: 3a12fc61af5c ("390x/s390-virtio-ccw: use memdev for RAM")
> Reported-by: Lukáš Doktor <ldoktor@redhat.com>
> Cc: Igor Mammedov <imammedo@redhat.com>
> Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> ---
>  hw/s390x/s390-skeys.c        |  2 +-
>  hw/s390x/s390-stattrib-kvm.c |  4 ++--
>  hw/s390x/s390-virtio-ccw.c   | 21 +++++++++++++++++++++
>  hw/s390x/sclp.c              | 17 +++++------------
>  include/hw/boards.h          |  7 +++++++
>  softmmu/vl.c                 |  3 +++
>  6 files changed, 39 insertions(+), 15 deletions(-)

Thanks, applied to s390-fixes (with the fixup message fixed up.)

[I plan to send a pull request for s390-fixes tomorrow, so please let
me know if there are any further concerns.]