[Qemu-discuss] How to resolve "Failed to mmap" error?

[A223 A223]

Hello,

When attempting PCI passthrough of a USB controller using the
following parameter to qemu:
-device vfio-pci,host=05:00.0,bus=root.1,addr=00.5

I receive the following error:
qemu-system-x86_64: -device
vfio-pci,host=05:00.0,bus=root.1,addr=00.5: Failed to mmap
0000:05:00.0 BAR 2. Performance may be slow

Ultimately, the controller does somewhat work in the VM, but I am
suffering some performance and reliability issues with it, so I
suspect this error message is pointing to the issue.

How can I go about tracking down the root cause of this error?

I'm using the latest master commit of qemu as of this writing, bbc4c3f4f3.
Here is my full qemu command line:
./bin/release/native/x86_64-softmmu/qemu-system-x86_64 \
-machine q35 \
-nodefaults \
-cpu host,kvm=off,hv_relaxed,hv_spinlocks=0x1fff,hv_vapic,hv_time \
-smp cpus=8,sockets=1,cores=4  \
-m 8192 \
-enable-kvm \
-chardev stdio,id=seabios -device isa-debugcon,iobase=0x402,chardev=seabios \
-device ioh3420,bus=pcie.0,addr=1c.0,port=1,chassis=1,id=root.1 \
-device 
vfio-pci,host=02:00.0,bus=root.1,addr=00.0,x-vga=on,multifunction=on,romfile=m2000.rom
\
-device vfio-pci,host=02:00.1,bus=root.1,addr=00.1 \
-device vfio-pci,host=05:00.0,bus=root.1,addr=00.5 \
-drive file=/dev/disk/by-id/wwn-0x5989675867543d12,if=ide,format=raw \
-drive file=samsung-bak-final-snap.qcow2,snapshot=on,readonly=on,if=virtio \
-drive file=win_usb.qcow2,if=ide \
-usb -usbdevice host:0x045e:0x0719 \
-usbdevice tablet \
-device e1000,netdev=net0,mac=DE:AD:BE:EF:DF:29 -netdev tap,id=net0 \
-vga std

Thank you,

Andrew