x86/kvm: Pad RSB on VM transition

x86/kvm: Pad RSB on VM transition

This is a patch from:

	From: Tim Chen <tim.c.chen@linux.intel.com>
	Date: Thu, 30 Nov 2017 15:00:10 +0100
	Subject: [RHEL7.5 PATCH 05/35] x86/kvm: Pad RSB on VM transition

Add code to pad the local CPU's RSB entries to protect
from previous less privilege mode.

Orabug: 27344012
CVE: CVE-2017-5715

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.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>