Guests wont start with 15 pcie-root-port devices

[Brian Rak]

In 6.1, a guest with 15 empty pcie-root-port devices will not boot 
properly - it just hangs on "Guest has not initialized the display 
(yet).".  As soon as I remove the last pcie-root-port, the guest begins 
starting up normally.  My qemu command line:

/usr/libexec/qemu-kvm -name guest=xxx,debug-threads=on -S -object 
{"qom-type":"secret","id":"masterKey0","format":"raw","file":"/var/lib/libvirt/qemu/domain-29-xxx/master-key.aes"} 
-machine 
pc-q35-6.1,accel=kvm,usb=off,dump-guest-core=off,memory-backend=pc.ram 
-cpu Haswell-noTSX-IBRS -m 4096 -object 
{"qom-type":"memory-backend-ram","id":"pc.ram","size":4294967296} 
-overcommit mem-lock=off -smp 2,sockets=2,cores=1,threads=1 -uuid 
daf2c139-4991-4079-9b8a-b4c98fc675e0 -no-user-config -nodefaults 
-chardev socket,id=charmonitor,fd=31,server=on,wait=off -mon 
chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown 
-boot strict=on -device 
pcie-root-port,port=0x10,chassis=1,id=pci.1,bus=pcie.0,multifunction=on,addr=0x2 
-device 
pcie-root-port,port=0x11,chassis=2,id=pci.2,bus=pcie.0,addr=0x2.0x1 
-device 
pcie-root-port,port=0x12,chassis=3,id=pci.3,bus=pcie.0,addr=0x2.0x2 
-device 
pcie-root-port,port=0x13,chassis=4,id=pci.4,bus=pcie.0,addr=0x2.0x3 
-device 
pcie-root-port,port=0x14,chassis=5,id=pci.5,bus=pcie.0,addr=0x2.0x4 
-device 
pcie-root-port,port=0x15,chassis=6,id=pci.6,bus=pcie.0,addr=0x2.0x5 
-device 
pcie-root-port,port=0x16,chassis=7,id=pci.7,bus=pcie.0,addr=0x2.0x6 
-device 
pcie-root-port,port=0x17,chassis=8,id=pci.8,bus=pcie.0,addr=0x2.0x7 
-device 
pcie-root-port,port=0x18,chassis=9,id=pci.9,bus=pcie.0,multifunction=on,addr=0x3 
-device 
pcie-root-port,port=0x19,chassis=10,id=pci.10,bus=pcie.0,addr=0x3.0x1 
-device 
pcie-root-port,port=0x1a,chassis=11,id=pci.11,bus=pcie.0,addr=0x3.0x2 
-device 
pcie-root-port,port=0x1b,chassis=12,id=pci.12,bus=pcie.0,addr=0x3.0x3 
-device 
pcie-root-port,port=0x1c,chassis=13,id=pci.13,bus=pcie.0,addr=0x3.0x4 
-device 
pcie-root-port,port=0x1d,chassis=14,id=pci.14,bus=pcie.0,addr=0x3.0x5 
-device 
pcie-root-port,port=0x1e,chassis=15,id=pci.15,bus=pcie.0,addr=0x3.0x6 
-device qemu-xhci,id=usb,bus=pci.1,addr=0x0 -audiodev 
id=audio1,driver=none -vnc 
127.0.0.1:5410,websocket=41310,password=on,audiodev=audio1 -device 
cirrus-vga,id=video0,bus=pcie.0,addr=0x1 -device 
virtio-balloon-pci,id=balloon0,bus=pci.2,addr=0x0 -sandbox 
on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny 
-msg timestamp=on

The same guest XML that produced this worked fine in 5.2  I was able to 
bisect this down to this commit:


commit e2a6290aab578b2170c1f5909fa556385dc0d820
Author: Marcel Apfelbaum <marcel.apfelbaum@gmail.com>
Date:   Mon Aug 2 12:00:57 2021 +0300

    hw/pcie-root-port: Fix hotplug for PCI devices requiring IO

Although I can't say I really understand why that commit triggered it.