Re: [Qemu-devel] Can not hotplug device to pci-to-pci bridge using machine type older than 1.7

[Igor Mammedov]

On Thu, 25 Jan 2018 16:01:39 +0800
Fei Li <address@hidden> wrote:

> Hi,
> 
> After I hotplug a pci device to a pci2pci bridge (I use "pci.1") with 
> machine type 1.7 or older,
> I can not see the pci device via `lspci` in the guest, but can see it 
> via `info qtree` in the hmp.
> What's more, after I reboot the guest or hotplug another pci device to 
> pci.0, I can see the
> previous hotplugged pci device via `lspci`.
> 
> I use qemu v2.9.* (but machine type =1.7 or 1.6) and kernel 4.4.
> I also do the test on self-build qemu v1.7, v1.6 and kernel 4.4, the 
> same phenomenon.
> My qemu command line is as follows:
> /usr/bin/qemu-system-x86_64 -m 1024 -machine 
> pc-i440fx-1.7,accel=kvm,kernel_irqchip=on -enable-kvm \
> -smp sockets=1,cores=1,threads=1 -no-user-config -cpu Skylake-Client \
> -name "pci-hp-qemu" -monitor telnet:127.0.0.1:8848,server,nowait \
> -drive file=/opt/pcihp.qcow2,if=none,id=drive0,format=qcow2 \
> -device virtio-blk-pci,drive=drive0,id=sata0,bootindex=1 \
> -device pci-bridge,chassis_nr=1 \
> -device virtio-net-pci,bus=pci.1,addr=01,id=netdev1 \
> -device virtio-net-pci,bus=pci.0,addr=07,id=netdev2 \
> -boot order=c
> ...
> (qemu) device_add virtio-net-pci,bus=pci.1,addr=12,id=netdev12
> 
> Checking the qemu commit log, I see qemu v2.0 introduces the acpi based 
> pci hotplug
> support and enables hotplug for pci devices behind pci2pci bridges
> (upstream commit 99fd437d, 9e047b98 and db4728e6).
> 
> I also checked qemu v2.9 code, and notice there's a judge: if 
> use_acpi_pci_hotplug is true (MT >= 2.0),
> the code will update the hotplug_handler for *all buses* to PIIX4PMState 
> and uses
> acpi_pcihp_device_plug_cb as the hp callback; else, for MT<=1.7, the 
> code will only update the
> hotplug_handler for pci.0 and leave other buses continue to use its 
> default hp_handler: the
> pci2pci bridge and default callback: pci_bridge_dev_hotplug_cb => 
> shpc_device_hotplug_cb.
> With the latter shpc* hotplug callback, hotplug a pci device to a 
> pci2pci bridge, like pci.1, I can
> not be seen it in the guest via `lspci`.
> 
> I am just wondering whether the qemu code does not support the shpc 
> hotplug to pci2pci bridge,
Last time, it used to 'work' i.e. guest is notified but fails to init
hotplugged device due to lack of IO resources.

I'd suggest to start looking at issue from guest side and see what
SHPC driver does to figure out if something in QEMU/firmware needs
to be fixed.

> or the shpc spec does not support this.
> Could someone shed some light on me? Thanks a lot!
> 
> Have a nice day
> Fei
>