Description of problem:
Hotplug a memory device, but the installed memory(RAM) is not changed.

Version-Release number of selected component (if applicable):
virtio-win-prewhql-0.1-215
kernel-5.14.0-5.el9.x86_64
qemu-kvm-6.1.0-8.el9.x86_64

How reproducible:
100%

Steps to Reproduce:
1. boot up windows guest with balloon device, memory size is 4G
 -m 4096,maxmem=64G,slots=4 \
2. install balloon driver.
3.  hotplug a 1G memory device
{'execute': 'object-add', 'arguments': {'qom-type': 'memory-backend-ram', 'id': 'mem-plug', 'size': 1073741824}, 'id': 'rkYDy9sF'}
{"return": {}, "id": "rkYDy9sF"}
{"execute": "device_add", "arguments": {"driver": "pc-dimm", "id": "dimm-plug", "memdev": "mem-plug"}, "id": "c0Ag0e1B"}
{"return": {}, "id": "c0Ag0e1B"}
4. get physical memory via wmic cmd, the result is 5G.
wmic ComputerSystem get TotalPhysicalMemory
5. check installed memory in system
"Start" -> "System" -> "Installed memory(RAM)" ,the result is 4G.

Actual results:
The installed memory(RAM) doesn't change after hotplug a memory device.

Expected results:
The hotplug memory should be recognized by OS.

Additional info:
Test windows guest: win2012,win2016,win2019, all have this problem.