XENHVM amd64 mouse issue

[Nick Sayer]

I have 8.2-RC2 + the netfront patch and a XENHVM kernel. I note that I wind up with both ums0 and psm0, but it turns out neither appears to work. My VNC console works for text video and keyboard, but trying to run a moused for either device doesn't result in the text console mouse pointer moving. Mouse clicks do appear to do something, however. I don't ever see the psm device show up in the vmstat -i output, FWIW. 

Has anyone else seen anything similar?

I hope it's not that I've forgotten some elementary moused configuration step. :/