Bug 1828654

Description of problem:
Balloon doesn't work after hotunplug/hotplug balloon device

Version-Release number of selected component (if applicable):
qemu-kvm-4.2.0-19.module+el8.2.1+6306+6069c690.x86_64
kernel-4.18.0-193.el8.x86_64
virtio-win-prewhql-181

How reproducible:
100%

Steps to Reproduce:
1.boot win10-64 guest with 8G mem and balloon device.
-device virtio-balloon-pci,id=balloon0,bus=pci.5 \

2. balloon memory to 4G
(qemu) info balloon
balloon: actual=8192
(qemu) balloon 4096
(qemu) info balloon
balloon: actual=4096
==========> balloon works

3. delete balloon device 
(qemu) device_del balloon0

4. add balloon device
(qemu) device_add virtio-balloon-pci,bus=pci.5,id=balloon0

5. balloon memory to 5G after hotunplug/hotplug
(qemu) info balloon
balloon: actual=8192
(qemu) balloon 5120
(qemu) info balloon
balloon: actual=8192
(qemu) info balloon
balloon: actual=8192
(qemu) info balloon
balloon: actual=8192
=========>balloon didn't work


Actual results:
balloon didn't work after step5

Expected results:
balloon works after hotunplug/hotplug.

Additional info:
1. qemu command line:
/usr/libexec/qemu-kvm -name win10-64 -enable-kvm -m 8192 -smp 3,maxcpus=24,cores=12,threads=1,sockets=2 -nodefaults -cpu 'EPYC',hv_stimer,hv_synic,hv_vpindex,hv_reset,hv_relaxed,hv_spinlocks=0x1fff,hv_vapic,hv_time,hv-tlbflush,+kvm_pv_unhalt -rtc base=localtime,driftfix=none -boot order=cd,menu=on -monitor stdio -M q35 -vga std -vnc :11 -qmp tcp:0:4444,server,nowait \
-device piix3-usb-uhci,id=usb -device usb-tablet,id=input0 \
-device pcie-root-port,port=0x10,chassis=1,id=pci.1,bus=pcie.0,multifunction=on,addr=0x3 \
-device pcie-root-port,port=0x11,chassis=2,id=pci.2,bus=pcie.0,addr=0x3.0x1 \
-device pcie-root-port,port=0x12,chassis=3,id=pci.3,bus=pcie.0,addr=0x3.0x2 \
-device pcie-root-port,port=0x13,chassis=4,id=pci.4,bus=pcie.0,addr=0x3.0x3 \
-device pcie-root-port,port=0x14,chassis=5,id=pci.5,bus=pcie.0,addr=0x3.0x4 \
-blockdev driver=file,cache.direct=off,cache.no-flush=on,filename=win1064.qcow2,node-name=system_file \
-blockdev driver=qcow2,node-name=drive_system_disk,file=system_file \
-object iothread,id=thread0 -device virtio-blk-pci,iothread=thread0,drive=drive_system_disk,id=virtio-disk0,bootindex=0 \
-netdev tap,script=/etc/qemu-ifup,downscript=no,id=hostnet0,vhost=on,queues=4 \
-device virtio-net-pci,netdev=hostnet0,id=net0,mac=00:52:11:36:3f:0d,bus=pci.2,mq=on,vectors=10 \
-device virtio-balloon-pci,id=balloon0,bus=pci.5 \

2. if didn't do balloon operation before hotunplug/hotplug, can't hit this issue.

3. did not hit this issue on linux guest.