[Qemu-devel] [Question] Why doesn't PCIe hotplug work for Q35 machine?

[Gonglei (Arei)]

Hi,

I noticed that the qemu-2.1 release change log says
" PCIe: Basic hot-plug/hot-unplug support for Q35 machine."

And then I made a testing for the hotplugging function of Q35.
But I'm failed, and I got the dmesg log in guest os as below:

[ 159.035250] Pciehp 0000:05:00.0:pcie24: Button pressed on Slot (0 - 4)
[ 159.035274] Pciehp 0000:05:00.0:pcie24: Card present on Slot (0 - 4)
[ 159.036517] Pciehp 0000:05:00.0:pcie24: PCI slot #0 - 4 - powering on due to 
button press.
[ 159.188049] Pciehp 0000:05:00.0:pcie24: Failed to check link status
[ 159.201968] Pciehp 0000:05:00.0:pcie24: Card not present on Slot (0 - 4)
[ 159.202529] Pciehp 0000:05:00.0:pcie24: Already disabled on Slot (0 - 4)

Steps of testing:

#1. QEMU version:

        The lateset master tree source.

#2. Command line:

./qemu-system-x86_64 -enable-kvm -m 2048 -machine q35 -device 
ide-drive,bus=ide.2,drive=MacHDD \ 
 -drive id=MacHDD,if=none,file=/mnt/sdb/gonglei/image/redhat_q35.img -monitor 
stdio -vnc :10 -readconfig ../docs/q35-chipset.cfg
QEMU 2.0.93 monitor - type 'help' for more information
(qemu) device_add 
virtio-net-pci,id=nic2,bus=pcie-switch-downstream-port-1-1,addr=1.0
(qemu) info network
hub 0
 \ user.0: index=0,type=user,net=10.0.2.0,restrict=off
 \ e1000.0: index=0,type=nic,model=e1000,macaddr=52:54:00:12:34:56

#3. Guest OS:

        Both rhel-server-7.0-x86_64 and SLES-11-SP3-DVD-x86_64-GM.

#4. Content of ../docs/q35-chipset.cfg:

[snip]

##
# Example PCIe switch with two downstream ports
#
[device "pcie-switch-upstream-port-1"]
  driver = "x3130-upstream"
  bus = "ich9-pcie-port-4"
  addr = "00.0"

[device "pcie-switch-downstream-port-1-1"]
  driver = "xio3130-downstream"
  multifunction = "on"
  bus = "pcie-switch-upstream-port-1"
  addr = "00.0"
  port = "1"
  chassis = "5"

[device "pcie-switch-downstream-port-1-2"]
  driver = "xio3130-downstream"
  multifunction = "on"
  bus = "pcie-switch-upstream-port-1"
  addr = "00.1"
  port = "1"
  chassis = "6"

[device "ich9-ehci-1"]
  driver = "ich9-usb-ehci1"
  multifunction = "on"
  bus = "pcie.0"
  addr = "1d.7"

[snip]

BTW, except testing hotplug of downstream ports, I also test the root port
with "device_add virtio-net-pci,id=nic2,bus=ich9-pcie-port-1,addr=1.0", but
I got the same result.

Am I wrong in some places? Or a QEMU bug?  Thanks for any help.

Best regards,
-Gonglei