Set IBPB when running a different VCPU

Set IBPB when running a different VCPU

Picking up a change from:
From: Tim Chen <tim.c.chen@linux.intel.com>
Date: Thu, 30 Nov 2017 15:00:12 +0100
[RHEL7.5 PATCH 07/35] kvm: vmx: Set IBPB when running a different
 VCPU

Ensure an IBPB (Indirect branch prediction barrier) before every VCPU
switch.

Orabug: 27344012
CVE: CVE-2017-5715

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Jun Nakajima <jun.nakajima@intel.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: John Haxby <john.haxby@oracle.com>
Signed-off-by: Kirtikar Kashyap <kirtikar.kashyap@oracle.com>