Linux kernel built with the KVM virtualisation support(CONFIG_KVM),
with nested virtualisation(nVMX) feature enabled(nested=1), is vulnerable
to a crash due to disabled external interrupts. As L2 guest could access(r/w)
hardware CR8 register of the host(L0).
In a nested virtualisation setup, L2 guest user could use this flaw
to potentially crash the host(L0) resulting in DoS.
