How to enable CONFIG_EXT4_ENCRYPTION

Hi!

I use xfstests with ext4 fs to test, and i found a skip:

ext4/024         [not run] kernel does not support ext4 encryption

I have rebuild config with CONFIG_FS_ENCRYPTION and CONFIG_EXT4_ENCRYPTION.
I try to set them both y and both m, but two ways both do not set and do not find related failure log.
I use v4.13-rc3 kernel to build.

Do i miss some dependence kconfig?

Thanks
Xiang