[PATCH v1 0/5] virtio-mem: s390x support

[David Hildenbrand]

Let's finally add s390x support for virtio-mem; my last RFC was sent
4 years ago, and a lot changed in the meantime.

This is based on mm/stable.

I sent out the QEMU part earlier today [1], that contains some more details
and a usage example on s390x (last patch).

There is not too much in here: The biggest part is querying a new diag(500)
STORAGE_LIMIT hypercall to obtain the proper "max_physmem_end". Once this
and the QEMU part will go upstream, it will get documented in [2]

The last two patches are not strictly required but certainly nice-to-have.

Note that -- in contrast to standby memory -- virtio-mem memory must be
configured to be automatically onlined as soon as hotplugged. The easiest
approach is using the "memhp_default_state=" kernel parameter or by using
proper udev rules. More details can be found at [3].

I have reviving+upstreaming a systemd service to handle configuring
that on my todo list, but for some reason I keep getting distracted ...

I tested various things, including:
 * Various memory hotplug/hotunplug combinations
 * Device hotplug/hotunplug
 * /proc/iomem output
 * reboot
 * kexec
 * kdump: make sure we don't hotplug memory

One remaining work item is kdump support for virtio-mem memory. I
am working on a prototype that will be fairly straight forward,
because the virtio-mem driver already supports a special kdump mode and
dracut will already include it in the initrd as default. With
holiday and conferences coming up I rather sent this out now.

[1] https://lkml.kernel.org/r/20240910175809.2135596-1-david@xxxxxxxxxx
[2] https://gitlab.com/davidhildenbrand/s390x-os-virt-spec
[3] https://virtio-mem.gitlab.io/user-guide/user-guide-linux.html

Cc: Heiko Carstens <hca@xxxxxxxxxxxxx>
Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Cc: Alexander Gordeev <agordeev@xxxxxxxxxxxxx>
Cc: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx>
Cc: Sven Schnelle <svens@xxxxxxxxxxxxx>
Cc: Thomas Huth <thuth@xxxxxxxxxx>
Cc: Cornelia Huck <cohuck@xxxxxxxxxx>
Cc: Janosch Frank <frankja@xxxxxxxxxxxxx>
Cc: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
Cc: Jason Wang <jasowang@xxxxxxxxxx>
Cc: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
Cc: "Eugenio Pérez" <eperezma@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

David Hildenbrand (5):
  s390/kdump: implement is_kdump_kernel()
  s390/physmem_info: query diag500(STORAGE_LIMIT) to support QEMU/KVM
    memory devices
  virtio-mem: s390x support
  lib/Kconfig.debug: default STRICT_DEVMEM to "y" on s390x
  s390/sparsemem: reduce section size to 128 MiB

 arch/s390/boot/physmem_info.c        | 46 ++++++++++++++++++++++++++--
 arch/s390/include/asm/kexec.h        |  4 +++
 arch/s390/include/asm/physmem_info.h |  3 ++
 arch/s390/include/asm/sparsemem.h    |  2 +-
 arch/s390/kernel/crash_dump.c        |  6 ++++
 drivers/virtio/Kconfig               | 12 ++++----
 lib/Kconfig.debug                    |  2 +-
 7 files changed, 64 insertions(+), 11 deletions(-)

-- 
2.46.0