Re: [Qemu-arm] ARM virt machine boots fail with 14 ioh3420

[Laszlo Ersek]

On 04/14/17 04:41, Shannon Zhao wrote:
> Hi Laszlo,
> 
> Thanks a lot for your reply:)
> 
> On 2017/4/14 1:09, Laszlo Ersek wrote:
>> Adding Andrea, Ard, Drew and Marcel; and the main qemu list
>>
>> On 04/13/17 09:37, Shannon Zhao wrote:
>>> Hi,
>>>
>>> I'm testing the PCIe devices hotplug for ARM virt machine and using
>>> ioh3420 as root port. I found that below command line could work.
>>>
>>> qemu-system-aarch64 -machine virt,accel=kvm,usb=off -cpu host -bios
>>> QEMU_EFI.fd -m 12288 -smp 8,sockets=8,cores=1,threads=1  -device
>>> ioh3420,port=0x8,chassis=1,id=pci.1,bus=pcie.0,addr=0x1 -device
>>> ioh3420,port=0x9,chassis=2,id=pci.2,bus=pcie.0,addr=0x2 -device
>>> ioh3420,port=0xa,chassis=3,id=pci.3,bus=pcie.0,addr=0x3 -device
>>> ioh3420,port=0xb,chassis=4,id=pci.4,bus=pcie.0,addr=0x4 -device
>>> ioh3420,port=0xc,chassis=5,id=pci.5,bus=pcie.0,addr=0x5 -device
>>> ioh3420,port=0xd,chassis=6,id=pci.6,bus=pcie.0,addr=0x6 -device
>>> ioh3420,port=0xe,chassis=7,id=pci.7,bus=pcie.0,addr=0x7 -device
>>> ioh3420,port=0xf,chassis=8,id=pci.8,bus=pcie.0,addr=0x8 -device
>>> ioh3420,port=0x10,chassis=9,id=pci.9,bus=pcie.0,addr=0x9 -device
>>> ioh3420,port=0x11,chassis=10,id=pci.10,bus=pcie.0,addr=0xa -device
>>> ioh3420,port=0x12,chassis=11,id=pci.11,bus=pcie.0,addr=0xb -device
>>> ioh3420,port=0x13,chassis=12,id=pci.12,bus=pcie.0,addr=0xc -device
>>> ioh3420,port=0x14,chassis=13,id=pci.13,bus=pcie.0,addr=0xd -device
>>> i82801b11-bridge,id=pci.17,bus=pcie.0,addr=0x11 -device
>>> pci-bridge,chassis_nr=18,id=pci.18,bus=pci.17,addr=0x0 -device
>>> usb-ehci,id=usb,bus=pci.18,addr=0x1 -device
>>> virtio-scsi-pci,id=scsi0,bus=pci.1,addr=0x0,disable-legacy=on,disable-modern=off
>>> -drive
>>> file=/mnt/sdb/guest.raw,format=raw,if=none,id=drive-scsi0-0-0-0,cache=none,aio=native
>>> -device
>>> scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0-0-0-0,id=scsi0-0-0-0,bootindex=1
>>> -netdev tap,id=hostnet1,vhost=on -device
>>> virtio-net-pci,netdev=hostnet1,id=net1,mac=00:16:3e:2b:cc:e1,bus=pci.2,addr=0x0,disable-legacy=on,disable-modern=off
>>> -netdev tap,id=hostnet2,vhost=on -device
>>> virtio-net-pci,netdev=hostnet2,id=net2,mac=00:16:3e:22:29:80,bus=pci.3,addr=0x0,disable-legacy=on,disable-modern=off
>>> -netdev tap,id=hostnet3,vhost=on -device
>>> virtio-net-pci,netdev=hostnet3,id=net3,mac=00:16:3e:28:07:9a,bus=pci.4,addr=0x0,disable-legacy=on,disable-modern=off
>>> -netdev tap,id=hostnet4,vhost=on -device
>>> virtio-net-pci,netdev=hostnet4,id=net4,mac=00:16:3e:3d:cd:b6,bus=pci.5,addr=0x0,disable-legacy=on,disable-modern=off
>>> -netdev tap,id=hostnet5,vhost=on -device
>>> virtio-net-pci,netdev=hostnet5,id=net5,mac=00:16:3e:64:9f:b0,bus=pci.6,addr=0x0,disable-legacy=on,disable-modern=off
>>> -netdev tap,id=hostnet6,vhost=on -device
>>> virtio-net-pci,netdev=hostnet6,id=net6,mac=00:16:3e:33:5b:d3,bus=pci.7,addr=0x0,disable-legacy=on,disable-modern=off
>>> -netdev tap,id=hostnet7,vhost=on -device
>>> virtio-net-pci,netdev=hostnet7,id=net7,mac=00:16:3e:39:7c:df,bus=pci.8,addr=0x0,disable-legacy=on,disable-modern=off
>>> -netdev tap,id=hostnet8,vhost=on -device
>>> virtio-net-pci,netdev=hostnet8,id=net8,mac=00:16:3e:0a:c1:4e,bus=pci.9,addr=0x0,disable-legacy=on,disable-modern=off
>>> -netdev tap,id=hostnet9,vhost=on -device
>>> virtio-net-pci,netdev=hostnet9,id=net9,mac=00:16:3e:0a:58:a6,bus=pci.10,addr=0x0,disable-legacy=on,disable-modern=off
>>> -netdev tap,id=hostnet10,vhost=on -device
>>> virtio-net-pci,netdev=hostnet10,id=net10,mac=00:16:3e:35:b5:80,bus=pci.11,addr=0x0,disable-legacy=on,disable-modern=off
>>> -netdev tap,id=hostnet11,vhost=on -device
>>> virtio-net-pci,netdev=hostnet11,id=net11,mac=00:16:3e:4d:b5:bb,bus=pci.12,addr=0x0,disable-legacy=on,disable-modern=off
>>> -netdev tap,id=hostnet12,vhost=on -device
>>> virtio-net-pci,netdev=hostnet12,id=net12,mac=00:16:3e:3b:69:e9,bus=pci.13,addr=0x0,disable-legacy=on,disable-modern=off
>>> -nographic
>>>
>>> But if I add one more ioh3420 device by appending above command with
>>> "-device ioh3420,port=0x15,chassis=14,id=pci.14,bus=pcie.0,addr=0xe",
>>> the guest can't boot. It seems that the firmware doesn't recognize the
>>> PCIe devices and print "Connect: PciRoot(0x0): Not Found".
>>>
>>> I'm using QEMU 2.8.1 and edk2 at commit 36a0d5c. Is there any limitation
>>> of the supported PCIe devices?
>>
>> In one sentence: you are running out of (emulated) IO space.
>>
>> Aarch64 does not have "IO space", but with QEMU, using the "virt"
>> machine type, we emulate 64KB of IO space, mapped to a special MMIO
>> range. This is available for PCI resource allocation, for such devices
>> that have IO BARs (and for such PCI bridges that reserve IO space for
>> hotplug purposes).
>>
>> The ioh3420 PCI Express Root Port device represents such a bridge. Even
>> if you plug a PCI Express device into it that has only MMIO BARs, the
>> bridge still advertises IO support, and it causes the firmware (and/or
>> Linux) to reserve 4KB of IO space. With ~15-16 such ports, you run out
>> of the 64 KB IO aperture, and the resource assignment fails.
>>
> So currently if we want to support more than ~15 virtio-net-pci devices,
> they can't connect to root port.

Right.

> They should connect to pcie root bus
> directly, right?

Correct, that will make them integrated endpoints, and no PCI Express
ports will be necessary (hence no IO space will be wasted).

> But this will not support hot-plug/remove.

Correct.

> 
> BTW, I think even though the qemu assign more than ~15 root port, I
> think the firmware should enable the first 15 ports and continue to work
> instead of failing with silence.

PCI device enumeration & resource assignment are implemented in
"MdeModulePkg/Bus/Pci/PciBusDxe". It is a generic edk2 driver that is
built into OVMF, ArmVirtQemu, and (supposedly) most physical platform
firmware, without any changes. If you have improvements in mind, please
submit a patch for that driver.

> 
>> The solution to this problem comes together from several parts:
>>
>> (1) New, vendor-independent device models in QEMU, for PCI Express Root
>> Ports and Downstream Ports, that (optionally) do not advertise any
>> support at all for IO BARs. This is on Marcel's task list. Please refer to:
>>
>>   generic port device model:
>>     https://bugzilla.redhat.com/show_bug.cgi?id=1390316
>>
> I see this is in upstream qemu.

Yes. All of the pertaining work will be implemented upstream first.

> 
>>   optional disablement of IO space:
>>     https://bugzilla.redhat.com/show_bug.cgi?id=1344299
>>
> Marcel, what's the status of this feature?

(I think Marcel plans to answer your question, but AIUI he too might
have a bit of post-vacation email backlog to flush.)

Thanks
Laszlo