CentOS 7
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SPICE Server
Install Desktop Virtualization "SPICE ( Simple Protocol for Independent Computing Environment )". It's possible to connect to virtual machines from remote client computer.
[1] Install SPICE Server if it's not installed yet. ( Normally it's already installed with KVM for dependency )
[root@dlp ~]#
yum -y install spice-server spice-protocol

[2] Edit existing virtual machine's xml-file and start virtual machine with SPICE like follows. This site's example has created a virtual machine without graphics, so it's OK to change settings like follows, but if you created virtual machine with a graphics, Remove "<graphics>***" and "<video>***" sections in xml file because qxl is used for graphics.
[root@dlp ~]#
virsh edit centos7
# edit the configration of "centos7"
<domain type='kvm'>
  <memory unit='KiB'>4194304</memory>
  <currentMemory unit='KiB'>4194304</currentMemory>
  <vcpu placement='static'>2</vcpu>
# add follows

# set any password for "passwd=***" section

# specify a uniq number for "sound" section "slot='0x06'"

# the "slot='0x02'" in video section is fixed number for graphics

    <graphics type='spice' port='5900' autoport='no' listen='' passwd='password'>
      <listen type='address' address=''/>
    <sound model='ac97'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
      <model type='qxl' ram='65536' vram='32768' heads='1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    <memballoon model='virtio'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>

Domain centos7 XML configuration edited.

[root@dlp ~]#
virsh start centos7
# start VM

Domain centos7 started
[4] By the way, if you'd like to enable SPICE on initial creating of virtual machine, specify like follows. Then, it's possible to install Systems with SPICE which requires GUI like Windows without installing Desktop Environment on KVM Host computer.
[root@dlp ~]#
virt-install \
--name Win2k12R2 \
--ram 6144 \
--disk path=/var/kvm/images/Win2k12R2.img,size=100 \
--vcpus=4 \
--os-type windows \
--os-variant=win2k12r2 \
--network bridge=br0 \
--graphics spice,listen=,password=password,keymap=en \
--video qxl \
[5] If Firewalld is running, allow SPICE port which you asgined to a virtual machine.
[root@dlp ~]#
firewall-cmd --add-port=5900/tcp --permanent

[root@dlp ~]#
firewall-cmd --reload