How to efficiently share host's folder with KVM guests?
CIFS can do extended attributes. You can set it up with Samba on Linux.
If your problem is throughput, you might benefit from increasting the max packet size. It defaults to 8 KiB (msize=8192).
The optimal value might take some experimentation, and can vary depending on your usage and the underlying filesystem, but I found 256 KiB (msize=262144) to work well for my purposes. That brought throughput up from ~150 MB/s to ~1.5 GB/s.
See also: https://lime-technology.com/forum/index.php?topic=36345.15