Works for me on qemu-5.2.0-0.7.rc2.fc34.x86_64, libvirt v6.10.0-61-gd8c9cc3bd0 with this series patched:

guest kernel: kernel-5.10.0-0.rc5.20201125git127c501a03d5.85.fc33.x86_64 recompiled with VIRTIO_PMEM

Steps:

1. Start VM with <maxMemory> and <numa>:

Domain xml:

...

</domain>

2. Attach the virtio memory device:

➜ ~ cat /tmp/virtio-mem.xml
<memory model='virtio'>
<target>
<size unit='KiB'>4194304</size>
<node>0</node>
<block unit='KiB'>2048</block>
<requested unit='KiB'>524288</requested>
</target>
</memory>

➜ ~ virsh attach-device pc /tmp/virtio-mem.xml
Device attached successfully

Before memory attached, the VM memory is:

[root@localhost ~]# free -m
total used free shared buff/cache available
Mem: 879 124 601 2 152 615
Swap: 0 0 0

After:

[root@localhost ~]# free -m
total used free shared buff/cache available
Mem: 1391 132 1106 2 153 1074
Swap: 0 0 0

3. Attach the virtio pmem device:

➜ ~ cat /tmp/virtio-pmem.xml
<memory model='virtio' access='shared'>
<source>
<path>/tmp/virtio_pmem</path>
<pmem/>
</source>
<target>
<size unit='KiB'>524288</size>
</target>
</memory>

➜ ~ virsh attach-device pc /tmp/virtio-pmem.xml
Device attached successfully

Check it in VM:

[root@localhost ~]# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
vda 252:0 0 10G 0 disk
└─vda1 252:1 0 10G 0 part /
pmem0 259:0 0 512M 0 disk

3. Try to detach them:

➜ ~ virsh detach-device pc /tmp/virtio-mem.xml
error: Failed to detach device from /tmp/virtio-mem.xml
error: internal error: unable to execute QEMU command 'device_del': virtio based memory devices cannot be unplugged.

➜ ~ virsh detach-device pc /tmp/virtio-pmem.xml
error: Failed to detach device from /tmp/virtio-pmem.xml
error: internal error: unable to execute QEMU command 'device_del': virtio based memory devices cannot be unplugged.

On Fri, Nov 27, 2020 at 11:05 PM Michal Privoznik <mprivozn@redhat.com> wrote:

Available also here:

https://gitlab.com/MichalPrivoznik/libvirt/-/commits/virtio_mem/

There are new virtio variants of pc-dimm and nvdimm devices. This is the
first attempt to impalement support for them in libvirt.

Thanks to David Hildenbrand for his valuable input!

Michal Prívozník (26):
viruuid: Rework virUUIDIsValid()
internal.h: Introduce VIR_IS_POW2()
docs: Fix nvdimm example wrt to <uuid/>
domain_conf: Check NVDIMM UUID in ABI stability
qemu_domain_address: Reformat qemuDomainAssignS390Addresses()
conf: Require nvdimm path in validate step
domain_conf: Fix virDomainMemoryModel type
virDomainMemorySourceDefFormat: Utilize virXMLFormatElement()
virDomainMemoryTargetDefFormat: Utilize virXMLFormatElement()
qemu: Move mem validation into post parse validator
conf: Move some of virDomainMemoryDef members into a union
conf: Introduce virtio-pmem <memory/> model
qemu_capabilities: Introduce QEMU_CAPS_DEVICE_VIRTIO_{P}MEM_PCI
qemu_validate: Require virtio-mem device for mem model virtio
security: Relabel virtio mem
qemu: Allow virtio-pmem in CGroups
qemu: Create virtio-pmem in domain namespace
qemu_command: Move dimm into qemuBuildDeviceAddressStr()
qemu: Build command line for virtio-pmem
conf: Introduce virtio-mem <memory/> model
qemu: Build command line for virtio-mem
qemu: Wire up <memory/> live update
qemu: Wire up MEMORY_DEVICE_SIZE_CHANGE event
qemu: Refresh the actual size of virtio-mem on monitor reconnect
virsh: Simplify @flags handing in cmdSetmem() and cmdSetmaxmem()
virsh: Introduce --virtio to setmem

docs/formatdomain.rst | 70 +++-
docs/schemas/domaincommon.rng | 16 +
src/conf/domain_conf.c | 372 ++++++++++++++----
src/conf/domain_conf.h | 38 +-
src/internal.h | 10 +
src/libvirt_private.syms | 2 +
src/qemu/qemu_alias.c | 59 ++-
src/qemu/qemu_capabilities.c | 4 +
src/qemu/qemu_capabilities.h | 2 +
src/qemu/qemu_cgroup.c | 43 +-
src/qemu/qemu_command.c | 172 +++++---
src/qemu/qemu_command.h | 5 +-
src/qemu/qemu_domain.c | 99 +++--
src/qemu/qemu_domain.h | 1 +
src/qemu/qemu_domain_address.c | 98 +++--
src/qemu/qemu_domain_address.h | 3 +-
src/qemu/qemu_driver.c | 198 +++++++++-
src/qemu/qemu_hotplug.c | 22 +-
src/qemu/qemu_hotplug.h | 5 +
src/qemu/qemu_monitor.c | 37 ++
src/qemu/qemu_monitor.h | 27 ++
src/qemu/qemu_monitor_json.c | 94 +++--
src/qemu/qemu_monitor_json.h | 5 +
src/qemu/qemu_namespace.c | 19 +-
src/qemu/qemu_process.c | 52 ++-
src/qemu/qemu_validate.c | 78 ++--
src/security/security_apparmor.c | 35 +-
src/security/security_dac.c | 48 ++-
src/security/security_selinux.c | 48 ++-
src/security/virt-aa-helper.c | 22 +-
src/util/virrandom.c | 2 +-
src/util/viruuid.c | 17 +-
src/util/viruuid.h | 2 +-
.../caps_4.1.0.x86_64.xml | 1 +
.../caps_4.2.0.x86_64.xml | 1 +
.../caps_5.0.0.x86_64.xml | 1 +
.../caps_5.1.0.x86_64.xml | 2 +
.../caps_5.2.0.x86_64.xml | 2 +
...mory-hotplug-virtio-mem.x86_64-latest.args | 53 +++
.../memory-hotplug-virtio-mem.xml | 78 ++++
...ory-hotplug-virtio-pmem.x86_64-latest.args | 45 +++
.../memory-hotplug-virtio-pmem.xml | 54 +++
tests/qemuxml2argvtest.c | 2 +
...emory-hotplug-virtio-mem.x86_64-latest.xml | 1 +
...mory-hotplug-virtio-pmem.x86_64-latest.xml | 1 +
tests/qemuxml2xmltest.c | 3 +
tools/virsh-domain.c | 138 ++++++-
47 files changed, 1703 insertions(+), 384 deletions(-)
create mode 100644 tests/qemuxml2argvdata/memory-hotplug-virtio-mem.x86_64-latest.args
create mode 100644 tests/qemuxml2argvdata/memory-hotplug-virtio-mem.xml
create mode 100644 tests/qemuxml2argvdata/memory-hotplug-virtio-pmem.x86_64-latest.args
create mode 100644 tests/qemuxml2argvdata/memory-hotplug-virtio-pmem.xml
create mode 120000 tests/qemuxml2xmloutdata/memory-hotplug-virtio-mem.x86_64-latest.xml
create mode 120000 tests/qemuxml2xmloutdata/memory-hotplug-virtio-pmem.x86_64-latest.xml

--
2.26.2

Tested-by: Han Han <hhan@redhat.com>