KVM: Add build-time error check on kvm_run size

It's already going to reach 2400 Bytes (which is over half of page
size on 4K page archs), so maybe it's good to have this build-time
check in case it overflows when adding new fields.
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

virt/kvm/kvm_main.c

@@ -2710,6 +2710,7 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
 		goto vcpu_decrement;
 	}
 
+	BUILD_BUG_ON(sizeof(struct kvm_run) > PAGE_SIZE);
 	page = alloc_page(GFP_KERNEL | __GFP_ZERO);
 	if (!page) {
 		r = -ENOMEM;