ARM: KVM: add architecture specific hook for capabilities

Most of the capabilities are common to both arm and arm64, but
we still need to handle the exceptions.

Introduce kvm_arch_dev_ioctl_check_extension, which both architectures
implement (in the 32bit case, it just returns 0).

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@cs.columbia.edu>
diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index 6c2a35d..dcfcbf5 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -214,6 +214,11 @@
 	kvm_call_hyp((void*)hyp_stack_ptr, vector_ptr, pgd_ptr);
 }
 
+static inline int kvm_arch_dev_ioctl_check_extension(long ext)
+{
+	return 0;
+}
+
 int kvm_perf_init(void);
 int kvm_perf_teardown(void);
 
diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index 6ea2aed..cc67caf 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -206,7 +206,7 @@
 		r = KVM_MAX_VCPUS;
 		break;
 	default:
-		r = 0;
+		r = kvm_arch_dev_ioctl_check_extension(ext);
 		break;
 	}
 	return r;