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Author SHA1 Message Date
Stefan Hajnoczi
aa3a285b5b Hi,
"Host Memory Backends" and "Memory devices" queue ("mem"):
 - Fixup handling of virtio-mem unplug during system resets, as
   preparation for s390x support (especially kdump in the Linux guest)
 - virtio-mem support for s390x
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Merge tag 'mem-2024-12-21' of https://github.com/davidhildenbrand/qemu into staging

Hi,

"Host Memory Backends" and "Memory devices" queue ("mem"):
- Fixup handling of virtio-mem unplug during system resets, as
  preparation for s390x support (especially kdump in the Linux guest)
- virtio-mem support for s390x

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* tag 'mem-2024-12-21' of https://github.com/davidhildenbrand/qemu:
  s390x: virtio-mem support
  s390x/virtio-ccw: add support for virtio based memory devices
  s390x: remember the maximum page size
  s390x/pv: prepare for memory devices
  s390x/s390-virtio-ccw: prepare for memory devices
  s390x/s390-skeys: prepare for memory devices
  s390x/s390-stattrib-kvm: prepare for memory devices and sparse memory layouts
  s390x/s390-hypercall: introduce DIAG500 STORAGE_LIMIT
  s390x: introduce s390_get_memory_limit()
  s390x/s390-virtio-ccw: move setting the maximum guest size from sclp to machine code
  s390x: rename s390-virtio-hcall* to s390-hypercall*
  s390x/s390-virtio-hcall: prepare for more diag500 hypercalls
  s390x/s390-virtio-hcall: remove hypercall registration mechanism
  s390x/s390-virtio-ccw: don't crash on weird RAM sizes
  virtio-mem: unplug memory only during system resets, not device resets

Conflicts:
- hw/s390x/s390-stattrib-kvm.c
  sysemu/ -> system/ header rename conflict.
- hw/s390x/virtio-ccw-mem.c
  Make Property array const and removed DEFINE_PROP_END_OF_LIST() to
  conform to the latest conventions.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2024-12-22 14:33:27 -05:00
David Hildenbrand
aa910c20ec s390x: virtio-mem support
Let's add our virtio-mem-ccw proxy device and wire it up. We should
be supporting everything (e.g., device unplug, "dynamic-memslots") that
we already support for the virtio-pci variant.

With a Linux guest that supports virtio-mem (and has automatic memory
onlining properly configured) the following example will work:

1. Start a VM with 4G initial memory and a virtio-mem device with a maximum
   capacity of 16GB:

   qemu/build/qemu-system-s390x \
    --enable-kvm \
    -m 4G,maxmem=20G \
    -nographic \
    -smp 8 \
    -hda Fedora-Server-KVM-40-1.14.s390x.qcow2 \
    -chardev socket,id=monitor,path=/var/tmp/monitor,server,nowait \
    -mon chardev=monitor,mode=readline \
    -object memory-backend-ram,id=mem0,size=16G,reserve=off \
    -device virtio-mem-ccw,id=vmem0,memdev=mem0,dynamic-memslots=on

2. Query the current size of virtio-mem device:

    (qemu) info memory-devices
    Memory device [virtio-mem]: "vmem0"
      memaddr: 0x100000000
      node: 0
      requested-size: 0
      size: 0
      max-size: 17179869184
      block-size: 1048576
      memdev: /objects/mem0

3. Request to grow it to 8GB (hotplug 8GB):

    (qemu) qom-set vmem0 requested-size 8G
    (qemu) info memory-devices
    Memory device [virtio-mem]: "vmem0"
      memaddr: 0x100000000
      node: 0
      requested-size: 8589934592
      size: 8589934592
      max-size: 17179869184
      block-size: 1048576
      memdev: /objects/mem0

4. Request to grow to 16GB (hotplug another 8GB):

    (qemu) qom-set vmem0 requested-size 16G
    (qemu) info memory-devices
    Memory device [virtio-mem]: "vmem0"
      memaddr: 0x100000000
      node: 0
      requested-size: 17179869184
      size: 17179869184
      max-size: 17179869184
      block-size: 1048576
      memdev: /objects/mem0

5. Try to hotunplug all memory again, shrinking to 0GB:

    (qemu) qom-set vmem0 requested-size 0G
    (qemu) info memory-devices
    Memory device [virtio-mem]: "vmem0"
      memaddr: 0x100000000
      node: 0
      requested-size: 0
      size: 0
      max-size: 17179869184
      block-size: 1048576
      memdev: /objects/mem0

6. If it worked, unplug the device

    (qemu) device_del vmem0
    (qemu) info memory-devices
    (qemu) object_del mem0

7. Hotplug a new device with a smaller capacity and directly size it to 1GB

    (qemu) object_add memory-backend-ram,id=mem0,size=8G,reserve=off
    (qemu) device_add virtio-mem-ccw,id=vmem0,memdev=mem0,\
                      dynamic-memslots=on,requested-size=1G
    (qemu) info memory-devices
    Memory device [virtio-mem]: "vmem0"
      memaddr: 0x100000000
      node: 0
      requested-size: 1073741824
      size: 1073741824
      max-size: 8589934592
      block-size: 1048576
      memdev: /objects/mem0

Trying to use a virtio-mem device backed by hugetlb into a !hugetlb VM
correctly results in the error:
   ... Memory device uses a bigger page size than initial memory

Note that the virtio-mem driver in Linux will supports 1 MiB (pageblock)
granularity.

Message-ID: <20241219144115.2820241-15-david@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
2024-12-21 20:15:06 +01:00