[PATCH v2 0/7] virtio-mem: s390 support

[David Hildenbrand <david@redhat.com>]

Let's finally add s390 support for virtio-mem; my last RFC was sent
4 years ago, and a lot changed in the meantime.

The latest QEMU series is available at [1], which contains some more
details and a usage example on s390 (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".

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 [2].

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. This will
be sent out separately once initial support landed.

[1] https://lkml.kernel.org/r/20241008105455.2302628-1-david@redhat.com
[2] https://virtio-mem.gitlab.io/user-guide/user-guide-linux.html

v1 -> v2:
* Document the new diag500 subfunction
* Use "s390" instead of "s390x" consistently

Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Thomas Huth <thuth@redhat.com>
Cc: Cornelia Huck <cohuck@redhat.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Cc: "Eugenio Pérez" <eperezma@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jonathan Corbet <corbet@lwn.net>

David Hildenbrand (7):
  s390/kdump: implement is_kdump_kernel()
  Documentation: s390-diag.rst: make diag500 a generic KVM hypercall
  Documentation: s390-diag.rst: document diag500(STORAGE LIMIT)
    subfunction
  s390/physmem_info: query diag500(STORAGE LIMIT) to support QEMU/KVM
    memory devices
  virtio-mem: s390 support
  lib/Kconfig.debug: default STRICT_DEVMEM to "y" on s390
  s390/sparsemem: reduce section size to 128 MiB

 Documentation/virt/kvm/s390/s390-diag.rst | 32 ++++++++++++----
 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 +-
 8 files changed, 89 insertions(+), 18 deletions(-)


base-commit: 6485cf5ea253d40d507cd71253c9568c5470cd27
-- 
2.46.1