x86/spectre_v2: Don't check microcode versions when running under hypervisors

x86/spectre_v2: Don't check microcode versions when running under hypervisors

commit 36268223c1e9981d6cfc33aff8520b3bde4b8114 upstream.

As:

 1) It's known that hypervisors lie about the environment anyhow (host
    mismatch)

 2) Even if the hypervisor (Xen, KVM, VMWare, etc) provided a valid
    "correct" value, it all gets to be very murky when migration happens
    (do you provide the "new" microcode of the machine?).

And in reality the cloud vendors are the ones that should make sure that
the microcode that is running is correct and we should just sing lalalala
and trust them.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: Wanpeng Li <kernellwp@gmail.com>
Cc: kvm <kvm@vger.kernel.org>
Cc: Krčmář <rkrcmar@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
CC: "H. Peter Anvin" <hpa@zytor.com>
CC: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20180226213019.GE9497@char.us.oracle.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>