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As Hyper-V Enlightenment feature is also supported on rhel6,so cloned the bug to rhel6.

+++ This bug was initially created as a clone of Bug #1083537 +++

+++ This bug was initially created as a clone of Bug #1083525 +++

Description of problem:
As of RHEL7.0 QEMU and Libvirt support several Hyper-V Enlightenment features, that need to be explicitly turned on for Windows guests. It is forbidden to turn them on for RHEL5 guests.
The QEMU flags are: "hv_relaxed,hv_spinlocks=0x1fff,hv_vapic,hv_time"

Additional info:
hv_relaxed turns off an internal Windows watchdog, and by doing so avoids some high load BSODs
hv_relaxed is also supported in RHEL6 as of RHEL6.4
All the other flags are performance optimization flags, that can improve the performance by 10% to much more (in extreme cases of resources overcommit).

Libvirt related bugs:
RHEL7
 Bug 1056205 - new cpu's flags, to control hyper-v related features - hv-time
 Bug 784836 - new cpu's flags, to control hyper-v related features
RHEL6
 Bug 864606 - [RFE] Enable Hyper-V Enlightenment for Windows guests

Note: You might want to duplicate this BZ to other RHEL7 based versions of RHOS.

I would prefer to not change the virt-manager defaults at this late point, closing as WONTFIX.  Please re-open if it is affecting any customer.