x86/svm: Set IBPB when running a different VCPU

x86/svm: Set IBPB when running a different VCPU

[RHEL7.5 PATCH 09/35] x86/svm: Set IBPB when running a different VCPU

Set IBPB (Indirect Branch Prediction Barrier) when the current CPU is
going to run a VCPU different from what was previously run.  Nested
virtualization uses the same VMCB for the second level guest, but the
L1 hypervisor should be using IBRS to protect itself.

Orabug: 27344012
CVE: CVE-2017-5715

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.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>