arm64: KVM: Add ARCH_WORKAROUND_2 discovery through ARCH_FEATURES_FUNC_ID

Now that all our infrastructure is in place, let's expose the
availability of ARCH_WORKAROUND_2 to guests. We take this opportunity
to tidy up a couple of SMCCC constants.

Acked-by: Christoffer Dall <christoffer.dall@arm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/kvm_host.h

@@ -455,6 +455,29 @@ static inline bool kvm_arm_harden_branch_predictor(void)
 	return cpus_have_const_cap(ARM64_HARDEN_BRANCH_PREDICTOR);
 }
 
+#define KVM_SSBD_UNKNOWN		-1
+#define KVM_SSBD_FORCE_DISABLE		0
+#define KVM_SSBD_KERNEL		1
+#define KVM_SSBD_FORCE_ENABLE		2
+#define KVM_SSBD_MITIGATED		3
+
+static inline int kvm_arm_have_ssbd(void)
+{
+	switch (arm64_get_ssbd_state()) {
+	case ARM64_SSBD_FORCE_DISABLE:
+		return KVM_SSBD_FORCE_DISABLE;
+	case ARM64_SSBD_KERNEL:
+		return KVM_SSBD_KERNEL;
+	case ARM64_SSBD_FORCE_ENABLE:
+		return KVM_SSBD_FORCE_ENABLE;
+	case ARM64_SSBD_MITIGATED:
+		return KVM_SSBD_MITIGATED;
+	case ARM64_SSBD_UNKNOWN:
+	default:
+		return KVM_SSBD_UNKNOWN;
+	}
+}
+
 void kvm_vcpu_load_sysregs(struct kvm_vcpu *vcpu);
 void kvm_vcpu_put_sysregs(struct kvm_vcpu *vcpu);