KVM: Get rid of return value from kvm_arch_create_vm_debugfs()

The general expectation with debugfs is that any initialization failure
is nonfatal. Nevertheless, kvm_arch_create_vm_debugfs() allows
implementations to return an error and kvm_create_vm_debugfs() allows
that to fail VM creation.

Change to a void return to discourage architectures from making debugfs
failures fatal for the VM. Seems like everyone already had the right
idea, as all implementations already return 0 unconditionally.

Acked-by: Marc Zyngier <[e-mail]>
Acked-by: Paolo Bonzini <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Oliver Upton <[e-mail]>

arch/powerpc/kvm/powerpc.c

···
 		vcpu->kvm->arch.kvm_ops->create_vcpu_debugfs(vcpu, debugfs_dentry);
 }
 
-int kvm_arch_create_vm_debugfs(struct kvm *kvm)
+void kvm_arch_create_vm_debugfs(struct kvm *kvm)
 {
 	if (kvm->arch.kvm_ops->create_vm_debugfs)
 		kvm->arch.kvm_ops->create_vm_debugfs(kvm);
-	return 0;
 }

arch/x86/kvm/debugfs.c

···
 	.release	= kvm_mmu_rmaps_stat_release,
 };
 
-int kvm_arch_create_vm_debugfs(struct kvm *kvm)
+void kvm_arch_create_vm_debugfs(struct kvm *kvm)
 {
 	debugfs_create_file("mmu_rmaps_stat", 0644, kvm->debugfs_dentry, kvm,
 			    &mmu_rmaps_stat_fops);
-	return 0;
 }

include/linux/kvm_host.h

···
 bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu);
 int kvm_arch_post_init_vm(struct kvm *kvm);
 void kvm_arch_pre_destroy_vm(struct kvm *kvm);
-int kvm_arch_create_vm_debugfs(struct kvm *kvm);
+void kvm_arch_create_vm_debugfs(struct kvm *kvm);
 
 #ifndef __KVM_HAVE_ARCH_VM_ALLOC
 /*

virt/kvm/kvm_main.c

···
 				    &stat_fops_per_vm);
 	}
 
-	ret = kvm_arch_create_vm_debugfs(kvm);
-	if (ret)
-		goto out_err;
-
+	kvm_arch_create_vm_debugfs(kvm);
 	return 0;
 out_err:
 	kvm_destroy_vm_debugfs(kvm);
···
  * Cleanup should be automatic done in kvm_destroy_vm_debugfs() recursively, so
  * a per-arch destroy interface is not needed.
  */
-int __weak kvm_arch_create_vm_debugfs(struct kvm *kvm)
+void __weak kvm_arch_create_vm_debugfs(struct kvm *kvm)
 {
-	return 0;
 }
 
 static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)