arm64: KVM: Support X-Gene guest VCPU on APM X-Gene host

This patch allows us to have X-Gene guest VCPU when using KVM arm64
on APM X-Gene host.

We add KVM_ARM_TARGET_XGENE_POTENZA for X-Gene Potenza compatible
guest VCPU and we return KVM_ARM_TARGET_XGENE_POTENZA in kvm_target_cpu()
when running on X-Gene host with Potenza core.

[maz: sanitized the commit log]

Signed-off-by: Anup Patel <anup.patel@linaro.org>
Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
index 3f0731e..0874557 100644
--- a/arch/arm64/kvm/guest.c
+++ b/arch/arm64/kvm/guest.c
@@ -207,20 +207,26 @@
 	unsigned long implementor = read_cpuid_implementor();
 	unsigned long part_number = read_cpuid_part_number();
 
-	if (implementor != ARM_CPU_IMP_ARM)
-		return -EINVAL;
+	switch (implementor) {
+	case ARM_CPU_IMP_ARM:
+		switch (part_number) {
+		case ARM_CPU_PART_AEM_V8:
+			return KVM_ARM_TARGET_AEM_V8;
+		case ARM_CPU_PART_FOUNDATION:
+			return KVM_ARM_TARGET_FOUNDATION_V8;
+		case ARM_CPU_PART_CORTEX_A57:
+			return KVM_ARM_TARGET_CORTEX_A57;
+		};
+		break;
+	case ARM_CPU_IMP_APM:
+		switch (part_number) {
+		case APM_CPU_PART_POTENZA:
+			return KVM_ARM_TARGET_XGENE_POTENZA;
+		};
+		break;
+	};
 
-	switch (part_number) {
-	case ARM_CPU_PART_AEM_V8:
-		return KVM_ARM_TARGET_AEM_V8;
-	case ARM_CPU_PART_FOUNDATION:
-		return KVM_ARM_TARGET_FOUNDATION_V8;
-	case ARM_CPU_PART_CORTEX_A57:
-		/* Currently handled by the generic backend */
-		return KVM_ARM_TARGET_CORTEX_A57;
-	default:
-		return -EINVAL;
-	}
+	return -EINVAL;
 }
 
 int kvm_vcpu_set_target(struct kvm_vcpu *vcpu,