[Qemu-discuss] xHCI controller/USB passthrough device - event ring full error on high packet rate

[Samuel Brian]

Hi all,

I'm looking for some help with a problem I'm having with Qemu USB 3.0 
passthrough with a Sierra Wireless MC7430 cellular modem.
In short, when I stress the modem with a high packet rate with small 
packets downstream using udpblast (the modem is receiving packets from 
the cellular network and passing them to the USB bus), I get the 
following error in my VM guest (Linux 4.14) almost immediately:

  xhci_hcd 0000:00:05.0: ERROR unknown event type 37
  xhci_hcd 0000:00:05.0: ERROR Transfer event TRB DMA ptr not part of 
current TD ep_index 12 comp_code 13
  xhci_hcd 0000:00:05.0: Looking for event-dma 0000000004cdab50 
trb-start 0000000004cda180 trb-end 0000000004cda180 seg-start 
0000000004cda000 seg-end 0000000004cdaff0
  ...

The transfer event errors continue for a while until the guest kernel 
gives up and stops talking to the modem.

Qemu gives me this error message before it sends that event type 37 
(CC_EVENT_RING_FULL_ERROR):

  xhci: ER 0 full, send ring full error

I think my problem is sort of mentioned in 
http://lists.nongnu.org/archive/html/qemu-devel/2017-02/msg00598.html

> It does suspious ERDP updates now and
> then (not every time, seems we must hit a race window for this to
> happen), which in turn makes the qemu xhci emulation think the event
> ring is full.  Things go south from here ...

I suppose I'm just really good at hitting that race window -- I can 
udpblast at 130,000 network packets per second over the modem when not 
running in a VM.

The most recent changes to Qemu that relate to the error I get are in 
http://lists.nongnu.org/archive/html/qemu-devel/2017-02/msg01095.html

Does anyone have any insight into these recent xHCI controller changes 
in regards to this problem I'm seeing?
Anyone help would be appreciated as I need to find a solution to this 
problem.

Sam

---

For reference, I'm using Qemu v2.10.1 and libusb 1.0.21 and running the 
VM on a Linux 4.14 host with:

  qemu-system-x86_64 --enable-kvm -nographic \
    -m 120M \
    -serial mon:stdio \
    -net nic,model=virtio -net tap,ifname=tap0script=no,downscript=no \
    -net nic,model=virtio -net tap,ifname=tap1,script=no,downscript=no \
    -drive file=$DISK,format=qcow2,if=virtio \
    -usb \
      -device usb-ehci,id=usb \
      -device usb-host,vendorid=0x1199,bus=usb.0