Goal
----

Test the presence of Intel CPU feature 'invtsc' (Invariant Time Stamp
Counter") in the guest CPU  *only* explicitly passing the CPU flag to
QEMU, which is possible via libvirt 'host-passthrough'  (in QEMU
parlance, it is "-cpu host+invtsc").   This can be verified by noticing
the presence of the flag "nonstop_tsc" when you run `cat /proc/cpuinfo`.  

When you don't explicitly specify the 'invtsc' flag to QEMU, you should
*not* see the presence of "nonstop_tsc" in the guest.


Test
====

When you run the script `host-passthrough_without_invtsc_CPU_flag.bash`,
and log into the guest, you will *not* see the "nonstop_tsc" feature
flag:

    $ cat /proc/cpuinfo | grep nonstop_tsc
    $ echo $?
    1


But when you run the script `host-passthrough_with_invtsc_CPU_flag.bash`,
and log into the guest, you will see the 'nonstop_tsc':

    $ cat /proc/cpuinfo | grep nonstop_tsc
    flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ss syscall nx pdpe1gb rdtscp lm constant_tsc up arch_perfmon rep_good nopl xtopology nonstop_tsc pni pclmulqdq ssse3 fma cx16 pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand hypervisor lahf_lm abm 3dnowprefetch arat xsaveopt fsgsbase bmi1 avx2 smep bmi2 erms



References
----------

(1) https://bugzilla.redhat.com/show_bug.cgi?id=1384124 --
    cpu flag nonstop_tsc is not present in guest with host-passthrough
    and feature policy require invtsc 

(2) https://bugzilla.redhat.com/show_bug.cgi?id=990051 --
    (NonstopTSCFlag) nonstop_tsc cpu flag support for KVM guests