KVM: VMX: Expose SSBD properly to guests.

The X86_FEATURE_SSBD is an synthetic CPU feature - that is
it bit location has no relevance to the real CPUID 0x7.EBX[31]
bit position. For that we need the new CPU feature name.

Fixes: 52817587 ("x86/cpufeatures: Disentangle SSBD enumeration")

CC: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: stable@vger.kernel.org
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

CVE-2018-3639 (x86)

(backported from https://patchwork.kernel.org/patch/10416823/)
[smb: context]
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

arch/x86/kvm/cpuid.c

@@ -359,7 +359,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 
 	/* cpuid 7.0.edx */
 	const u32 kvm_supported_7_0_edx_x86_features =
-		F(SPEC_CTRL) | F(SSBD);
+		F(SPEC_CTRL) | F(SPEC_CTRL_SSBD);
 
 	/* cpuid 0xD.1.eax */
 	const u32 kvm_supported_word10_x86_features =