uas drives connected to passed-through xhci controller hang in Windows guest

[Tom Yan]

Hi,

I've been having issues with uas (usb attached scsi) drive that is
connected to a pci passed-through xhci controller (ASM1142). The drive
hangs and cannot really be used. The combination seems to work fine on
bare-metal. bot/msc drives work fine.

I tried to install the XHCI driver from ASMedia to see if it makes a
difference. It ends up disabling uas. Not sure if that would happen on
bare-metal as well.

I saw 
https://github.com/torvalds/linux/commit/ec37198acca7b4c17b96247697406e47aafe0605
today and I wonder if vfio-pci needs to be "notified" as well. Never
tried passing through another XHCI controller.

Can anyone confirm the issue is vendor/device-specific? Any idea on
how to further debug this?

Regards,
Tom