x86/KVM/VMX: Expose SPEC_CTRL Bit(2) to the guest

x86/KVM/VMX: Expose SPEC_CTRL Bit(2) to the guest

Expose the CPUID.7.EDX[31] bit to the guest, and also guard against various
combinations of SPEC_CTRL MSR values.

The handling of the MSR (to take into account the host value of SPEC_CTRL
Bit(2)) is taken care of in patch:

  KVM/SVM/VMX/x86/spectre_v2: Support the combination of guest and host IBRS

OraBug: 28041771
CVE: CVE-2018-3639

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit da39556f66f5cfe8f9c989206974f1cb16ca5d7c)
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Mihai Carabas <mihai.carabas@oracle.com>
 Conflicts:
	arch/x86/kvm/cpuid.c
	arch/x86/kvm/vmx.c

Signed-off-by: Brian Maly <brian.maly@oracle.com>