Fix included in qemu-kvm-rhev-2.6.0-28.el7_3.2

Reproduce:
qemu-kvm-rhev-2.6.0-28.el7
kernel-3.10.0-534.el7.x86_64

Steps:
1. boot guest with virtio balloon device
# /usr/libexec/qemu-kvm -m 4G -smp 4 \

-drive file=rhel73-64-virtio.qcow2,format=qcow2,if=none,cache=none,id=drive0 -device virtio-blk-pci,drive=drive0,id=blk-pci0 \

-device virtio-balloon-pci,id=balloon0,guest-stats-polling-interval=2 \

-vnc :1  -monitor stdio -qmp tcp:0:4444,server,nowait

2. check guest stats from qmp
{"execute":"qmp_capabilities"}
{"return": {}}

{ "execute":"qom-get", "arguments":{"path":'/machine/peripheral/balloon0', "property": "guest-stats" } }
{"return": {"stats": {"stat-swap-out": 0, "stat-available-memory": 3279396864, "stat-free-memory": 3034173440, "stat-minor-faults": 1140989, "stat-major-faults": 1113, "stat-total-memory": 3974823936, "stat-swap-in": 0}, "last-update": 1482386437}}

3. migrate guest to dst host 

4. check guest stats again after migration 
{"execute":"qmp_capabilities"}
{"return": {}}

{ "execute":"qom-get", "arguments":{"path":'/machine/peripheral/balloon0', "property": "guest-stats" } }
{"return": {"stats": {"stat-swap-out": -1, "stat-available-memory": -1, "stat-free-memory": -1, "stat-minor-faults": -1, "stat-major-faults": -1, "stat-total-memory": -1, "stat-swap-in": -1}, "last-update": 0}}

The stats statistics return -1, so the bug is reproduced. 

Verify:
qemu-kvm-rhev-2.6.0-28.el7_3.2
kernel-3.10.0-534.el7.x86_64

With same steps as above, after step 4, the stats collection works well:

{"execute":"qmp_capabilities"}
{"return": {}}
{ "execute":"qom-get", "arguments":{"path":'/machine/peripheral/balloon0', "property": "guest-stats" } }
{"return": {"stats": {"stat-swap-out": 0, "stat-available-memory": 3266523136, "stat-free-memory": 3149885440, "stat-minor-faults": 1104492, "stat-major-faults": 1084, "stat-total-memory": 3974823936, "stat-swap-in": 0}, "last-update": 1482387680}}

So the bug is fixed.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHBA-2017-0115.html