KVM: Get an fd before creating the VM

Allocate a VM's fd at the very beginning of kvm_dev_ioctl_create_vm() so
that KVM can use the fd value to generate strigns, e.g. for debugfs,
when creating and initializing the VM.
Signed-off-by: Oliver Upton <oupton@google.com>
Message-Id: <20220720092259.3491733-4-oliver.upton@linux.dev>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

virt/kvm/kvm_main.c

@@ -4889,25 +4889,27 @@ EXPORT_SYMBOL_GPL(file_is_kvm);
 
 static int kvm_dev_ioctl_create_vm(unsigned long type)
 {
-	int r;
+	int r, fd;
 	struct kvm *kvm;
 	struct file *file;
 
+	fd = get_unused_fd_flags(O_CLOEXEC);
+	if (fd < 0)
+		return fd;
+
 	kvm = kvm_create_vm(type);
-	if (IS_ERR(kvm))
-		return PTR_ERR(kvm);
+	if (IS_ERR(kvm)) {
+		r = PTR_ERR(kvm);
+		goto put_fd;
+	}
+
 #ifdef CONFIG_KVM_MMIO
 	r = kvm_coalesced_mmio_init(kvm);
 	if (r < 0)
 		goto put_kvm;
 #endif
-	r = get_unused_fd_flags(O_CLOEXEC);
-	if (r < 0)
-		goto put_kvm;
-
 	file = anon_inode_getfile("kvm-vm", &kvm_vm_fops, kvm, O_RDWR);
 	if (IS_ERR(file)) {
-		put_unused_fd(r);
 		r = PTR_ERR(file);
 		goto put_kvm;
 	}
@@ -4918,18 +4920,20 @@ static int kvm_dev_ioctl_create_vm(unsigned long type)
 	 * cases it will be called by the final fput(file) and will take
 	 * care of doing kvm_put_kvm(kvm).
 	 */
-	if (kvm_create_vm_debugfs(kvm, r) < 0) {
-		put_unused_fd(r);
+	if (kvm_create_vm_debugfs(kvm, fd) < 0) {
 		fput(file);
-		return -ENOMEM;
+		r = -ENOMEM;
+		goto put_fd;
 	}
 	kvm_uevent_notify_change(KVM_EVENT_CREATE_VM, kvm);
 
-	fd_install(r, file);
-	return r;
+	fd_install(fd, file);
+	return fd;
 
 put_kvm:
 	kvm_put_kvm(kvm);
+put_fd:
+	put_unused_fd(fd);
 	return r;
 }