Description: Indirect Branch Prediction Barrier is force-disabled when STIBP is unavailable or enhanced IBRS is available.
References:
 https://lkml.org/lkml/2020/6/9/183
 https://www.openwall.com/lists/oss-security/2020/06/10/1
 https://bugzilla.redhat.com/show_bug.cgi?id=1845867
Notes:
 carnil> Commit fixes 7cc765a67d8e ("x86/speculation: Enable prctl mode
 carnil> for spectre_v2_user")
Bugs:
upstream: released (5.8-rc1) [21998a351512eba4ed5969006f0c55882d995ada]
4.19-upstream-stable: released (4.19.129) [5d9d55cf4733c5ced8e1d19ea242a128ab9612d2]
4.9-upstream-stable: released (4.9.228) [38be87f5e7a7a7378d4ef4528c13bd1d666ab867]
3.16-upstream-stable: ignored "EOL"
sid: released (5.7.6-1)
4.19-buster-security: released (4.19.131-1)
4.9-stretch-security: released (4.9.228-1)
3.16-jessie-security: ignored "EOL"