OverlayFS not working on top of VirtioFS

OverlayFS can't start on top of VirtioFS. Dmesg errors out with messages like this:

[    7.584761] overlayfs: upper fs does not support tmpfile.
[    7.585734] overlayfs: upper fs does not support xattr, falling back to index=off and metacopy=off.
[    7.585736] overlayfs: upper fs missing required features.

OverlayFS is kinda important for Docker... Devicemapper works, but still.

I was running virtiofsd (the Rust version) with the --xattr flag, but apparently it didn't help.