Windows DomU: PCIe passthrough issues

[Paul Leiber <paul@xxxxxxxxxxxxxxxx>]

Hi everybody,

after getting my Windows Server 2012 DomU up and running, I have problems with 
reliably passing through my PCIe TV tuner card (Hauppauge HVR-2205).

I mostly followed 
https://wiki.xenproject.org/wiki/Xen_PCI_Passthrough#:~:text=PCI%20passthrough%20allows%20you%20to,access%20to%20the%20PCI%20device.
 I need to set "permissive=1" and limit the Dom0 memory size. I then can pass 
through the card without any problem. It gets detected and works very well 
under Windows. However, sometimes the card gets "lost" in the DomU, i. e. it 
disappears from device manager and isn't functional anymore. This seems to 
happen mostly after a Windows reboot, but I have the impression that there were 
also instances without a reboot. I can than reattach it in Dom0 with "xl 
pci-attach" and it works again in the DomU.

Additional information:
- My TV software (MediaPortal) seems to sometimes recognize a new PCIe card 
instance after reboot/reattachment, but not consistently. (I then need to 
manually tell the media software to connect the already tuned channels to the 
"new" tuner card as well as an internal number of the tuner card is 
incremented.) Both of  this didn't happen with the bare metal system.
- I tested the card in a linux DomU (with VDR software) where the card was 
attached very reliably.
- The tuner card seems not to have function level reset capabilities (at least 
lspci shows FLReset- in the DevCap field, although I had the impression that I 
have seen there a FLReset+ in the past...).

What could be the reason for this behavior? What can I do to troubleshoot 
and/or solve this issue?

The boot entry has the following parameters:
dom0_mem=1024M,max:1024M xen-pciback.hide=(01:00.0)

Xen config file for the Windows domU:

# kernel = "/usr/lib/xen-4.0/boot/hvmloader"
type='hvm'
memory = 4096
vcpus=2
name = "matrix"
vif = ['bridge=xenbr0,mac=00:16:3E:54:A8:2B']
disk = ['phy:/dev/vg0/matrix,hda,w','phy:/dev/vg0/compudms-data,hdb,w']
device_model_version = 'qemu-xen'
boot="c"
hdtype = 'ahci'
acpi = 1
apic = 1
xen_platform_pci = 1
vendor_device = 'xenserver'
#  PCI Passthrough
pci=['01:00.0,permissive=1,power_mgmt=1']
viridian = 1
stdvga = 1
sdl = 0
#pae = 1
serial = 'pty'
usb = 1
#usbctrl = ["type = pv"]
usbdevice = 'tablet'
keymap = 'de'
#       VNC
#vnc = 1
#vnclisten = "0.0.0.0"
#vncpasswd = ""
# SPICE
spice=1
spicehost='0.0.0.0'
spiceport=6000
# spicedisable_ticketing enabled is for no spice password, instead use 
spicepasswd
spicedisable_ticketing=1
#spicepasswd="test"
spicevdagent=1
spice_clipboard_sharing=1
# this will automatically redirect up to 4 usb devices from spice client to 
domUs
#spiceusbredirection=4
# This adds intel hd audio emulated card used for spice audio
soundhw="hda"

xl info:

host                   : xxx
release                : 4.19.0-14-amd64
version                : #1 SMP Debian 4.19.171-2 (2021-01-30)
machine                : x86_64
nr_cpus                : 4
max_cpu_id             : 3
nr_nodes               : 1
cores_per_socket       : 4
threads_per_core       : 1
cpu_mhz                : 1992.095
hw_caps                : 
bfebfbff:77faf3ff:2c100800:00000121:0000000f:009c6fbf:00000000:00000100
virt_caps              : hvm hvm_directio
total_memory           : 32542
free_memory            : 18773
sharing_freed_memory   : 0
sharing_used_memory    : 0
outstanding_claims     : 0
free_cpus              : 0
xen_major              : 4
xen_minor              : 11
xen_extra              : .4
xen_version            : 4.11.4
xen_caps               : xen-3.0-x86_64 xen-3.0-x86_32p hvm-3.0-x86_32 
hvm-3.0-x86_32p hvm-3.0-x86_64
xen_scheduler          : credit
xen_pagesize           : 4096
platform_params        : virt_start=0xffff800000000000
xen_changeset          :
xen_commandline        : placeholder dom0_mem=1024M,max:1024M 
xen-pciback.hide=(01:00.0)
cc_compiler            : gcc (Debian 8.3.0-6) 8.3.0
cc_compile_by          : pkg-xen-devel
cc_compile_domain      : lists.alioth.debian.org
cc_compile_date        : Fri Dec 11 21:33:51 UTC 2020
build_id               : 6d8e0fa3ddb825695eb6c6832631b4fa2331fe41
xend_config_format     : 4

Logs from /var/log/xen, dmesg and /var/log/messages and Windows DomU didn't 
seem to show relevant errors, but can of course be provided if needed.

Best regards,

Paul