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

[Michael S. Tsirkin]

On Fri, Aug 15, 2014 at 07:33:29AM +0000, Gonglei (Arei) wrote:
> 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

I don't think you can use any slot except slot 0 for pci express.
> (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.

Same thing.

> Am I wrong in some places? Or a QEMU bug?  Thanks for any help.
> 
> Best regards,
> -Gonglei
> 

We might want to add a check for this, to produce a
better error message.

-- 
MST