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

[Knut Omang]

On Wed, 2014-08-20 at 06:39 +0200, Knut Omang wrote:
> On Wed, 2014-08-20 at 02:16 +0000, Gonglei (Arei) wrote:
> > > -----Original Message-----
> > > From: Michael S. Tsirkin [mailto:address@hidden
> > > Sent: Wednesday, August 20, 2014 5:19 AM
> > > To: Gonglei (Arei)
> > > Cc: Paolo Bonzini; Marcel Apfelbaum; address@hidden;
> > > address@hidden; address@hidden; Huangweidong (C)
> > > Subject: Re: [Question] Why doesn't PCIe hotplug work for Q35 machine?
> > > 
> > > On Tue, Aug 19, 2014 at 06:25:56AM +0000, Gonglei (Arei) wrote:
> > > > > >> Subject: Re: [Question] Why doesn't PCIe hotplug work for Q35 
> > > > > >> machine?
> > > > > >>
> > > > > >> On Sun, 2014-08-17 at 13:00 +0200, Michael S. Tsirkin wrote:
> > > > > >>> 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.
> > > > > >
> > > > > > OK. Does the PCIe specification say that?
> > > > > > I appreciate very much that you explain more.
> > > > >
> > > > > The closest I could find is in "7.3. Configuration Transaction
> > > > > Rules"/"7.3.1. Device Number":
> > > > >
> > > > > With non-ARI Devices, PCI Express components are restricted to
> > > > > implementing a single Device Number on their primary interface 
> > > > > (Upstream
> > > > > Port) [...] Downstream Ports that do not have ARI Forwarding enabled
> > > > > must associate only Device 0 with the device attached to the Logical 
> > > > > Bus
> > > > > representing the Link from the Port. Configuration Requests
> > > > > targeting the Bus Number associated with a Link specifying Device 
> > > > > Number
> > > > > 0 are delivered to the device attached to the Link; Configuration
> > > > > Requests specifying all other Device Numbers (1-31)
> > > > > must be terminated by the Switch Downstream Port or the Root Port with
> > > > > an Unsupported Request Completion Status (equivalent to Master Abort 
> > > > > in
> > > > > PCI).
> > > > >
> > > > Thanks a lot, Paolo.
> > > > And I found another issue when cold-plugging don't using slot 0, the 
> > > > PCIe
> > > device also can't
> > > > be searched in guest os.
> > > >
> > > > So, I have some questions and ideas:
> > > >
> > > > 1. Does qemu support ARI Forwarding for PCIe at present? If yes, how to
> > > enable it ?
> > > 
> > > What do you mean by forwarding?
> > 
> > Just ARI supporting, came from the PCIe spec.
> > 
> > > What would you like to do?
> > 
> > I just want to add some check. Because it made me confused, 
> > and other people IMHO.
> > 
> > > We do have code to emulate ARI, I don't think many people
> > > tested it so it's likely incomplete.
> > > 
> > Yes, you have said (pcie_ari_init).
> 
> I have actually been playing around with this a bit in the context of
> SR/IOV, and have some patches waiting to be posted. I haven't had any
> success with the downstream switch - as you indicate, pieces may be
> missing, but in my case, using the ioh3420 root port worked fine after
> setting the ARI forwarding capability and a few other minor fixes that
> may even be considered trivial patches. I will put my acts together and
> rebase these and post in a separate mail.
> 
> Basically I am able to run and hotplug an ARI capable device on any root
> port. So instead of using the downstream switch, you could just add
> another ioh3420 for your next device, if that suits your needs.
> 
> Note that there are two places to add "ARI support", one is the
> forwarding capability of bridges/switches, the other is the device's
> capability to be an ARI device, represented by the ARI PCIe capability.
> 
> > > > 2. If not, we should add some check for PCIe root ports and downstream
> > > ports,
> > > >  meanwhile add explaining document.
> > > 
> > > You want an attempt to add a device at slot !=0 to report an error?
> > > We can do this if device at slot 0 does not have ARI support.
> > > Seems like a low priority issue I think.
> 
> If I understand the spec right it is devices in slots > 0 that is

Sorry - just noticed that a confusing "not" was lost here - I meant:

"it is not devices in slots > 0 that are"

> limited, it is that each slot may only expose one device, even if that
> device has more than 8 functions and supports ARI, in which case we
> should create a master abort. But the better solution in my view would
> be just to implement ARI forwarding..

Knut

> > Hmm. I have post a patch you have seen. :)
> > 
> > > > 3. Those check should add in general code level, both hotplug and 
> > > > coldplug.
> > > 
> > > Generally it's not clear how we want to support hotplug for
> > > multifunction devices. One way it to add functions != 0 then
> > > add function 0 and notify guest.
> > > If so, then of course we can't check things ...
> > > 
> > Actually, I just check the device number is 0 or not, don't include 
> > functions.
> > 
> > BTW, I have tested a scenario: 
> > 
> > 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 \
> > -device virtio-net-pci,id=nic1,bus=pcie-switch-downstream-port-1-1,addr=0.1 
> >             #coldplug slot 0 function 1
> > QEMU 2.1.50 monitor - type 'help' for more information
> > (qemu) device_add 
> > virtio-net-pci,id=nic2,bus=pcie-switch-downstream-port-1-1,addr=0.0   
> > #hotplug slot 0 function 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
> > nic2: index=0,type=nic,model=virtio-net-pci,macaddr=52:54:00:12:34:58
> > (qemu)
> > 
> > And finally, the guest os only recognized nic2.
> > 
> > Best regards,
> > -Gonglei
> > 
> 
> 
>