Comment 31 for bug 1618473

ok so final update from me:

1. roll back this fix
2. propose the workaround to all affected customers, which is:
--1. check current model which libvirt chooses by doing "ps -ef | grep qemu" on any problematic compute, and look for --cpu directive, should look like "-cpu Westmere,+invpcid,+erms,+bmi2,+smep..." - save this parameter
--2. edit nova.conf:
----1. cpu_mode=custom
----2. cpu_model=<PASTE THE PARAMETER HERE, BUT REMOVE PROBLEMATIC EXTENSIONS, SUCH AS avx2>

Example:
cpu_model=Westmere,+invpcid,+erms,+bmi2,+smep,+bmi1,+fsgsbase,+abm,+rdtscp,+pdpe1gb,+rdrand,+f16c,+avx,+osxsave,+xsave,+tsc-deadline,+movbe,+pcid,+pdcm,+xtpr,+fma,+tm2,+est,+vmx,+ds_cpl,+monitor,+dtes64,+pclmuldq,+pbe,+tm,+ht,+ss,+acpi,+ds,+vme

If customers do not have problematic extensions in their cpu parameter, then they will have to use an earlier CPU model (can find one by looking at /usr/share/libvirt/cpu_map.xml) and will have to use it as the first word in the parameter, and manually determine and add all other extensions which appear in newer models, again possible by looking at cpu_map.xml file - it shows how newer CPU models derive from older and add features