[Qemu-devel] [Bug 1594239] Re: After adding more scsi disks for Aarch64 virtual machine, start the VM and got Qemu Error

["Laszlo Ersek \(Red Hat\)" <lersek@redhat.com>]

The issue is that virtio-mmio devices don't distinguish themselves on
the sysbus level.

Using the small reproducer from Cole, and setting a breakpoint on
virtio_bus_get_dev_path(), for the second virtio-scsi-device we get:

    ...
      qdev_get_dev_path()
        virtio_bus_get_dev_path()
          qdev_get_dev_path()

In virtio_bus_get_dev_path(), "bus" is set to "virtio-mmio-bus.30"
("name" field). "proxy" is set to the VirtIOMMIOProxy object that
produces (owns) "virtio-mmio-bus.30" as its "bus" field. Finally
virtio_bus_get_dev_path() forwards the "get dev path" request to this
proxy object.

In that second qdev_get_dev_path() call, the parent bus for the
VirtIOMMIOProxy object is "main-system-bus" (proxy->parent_bus->name).

The bus class for the main system bus is set up in
system_bus_class_init(), and that function only sets the "print_dev" and
"get_fw_dev_path" member functions. The "get_dev_path" member function
is left NULL, hence qdev_get_dev_path() will return NULL ultimately.

Thus, in the "dev/id" case, in your debug patch's terminology, "id" will
be NULL, and the inner concatenation branch will not be taken. Only
vmsd->name will be copied into se->idstr.

This can be fixed in two ways, I believe.

* First, we could implement sysbus_get_dev_path(), and set it in
system_bus_class_init(). This function would closely follow
sysbus_get_fw_dev_path(): format the address of the first MMIO or IO
region of the device to a string. For virtio-mmio devices in particular,
this would be suitable, because they have a single (0x200 size) memory
region (see VirtIOMMIOProxy.iomem), and the base address of that memory
region is precisely what distinguishes the virtio-mmio transports from
each other.

* Secondly, we could override virtio_bus_get_dev_path() in
virtio_mmio_bus_class_init(), as the "get_dev_path" member function of
the TYPE_VIRTIO_MMIO_BUS class. Implementing
virtio_mmio_bus_get_dev_path() would result in the first
qdev_get_dev_path() listed above to call our specialized code.

In virtio_mmio_bus_get_dev_path(), we could open-code the first two
steps of virtio_bus_get_dev_path():

    BusState *bus = qdev_get_parent_bus(dev);
    DeviceState *proxy = DEVICE(bus->parent);

Here we'd know that "proxy" (a VirtIOMMIOProxy object) is actually
derived from SysBusDevice, and we could dynamic-cast it accordingly. In
the SysBusDevice, we could access mmio[0].addr directly (it's a "public"
field, and we know virtio-mmio transports have exactly one MMIO region
and no IO regions), and format that.

The small issue with both alternatives is that they'd immediately break
migration between pre-patch and post-patch, because (IIUC) these paths
get formatted into migration section headers or some such. So either
change would require introducing new machine type versions for *all*
target arches and machine types that are currently versioned. This is
the reason I'm not trying to prototype either idea above -- just
gathering all those machine types looks daunting.

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https://bugs.launchpad.net/bugs/1594239

Title:
  After adding more scsi disks for Aarch64 virtual machine, start the VM
  and got Qemu Error

Status in QEMU:
  Confirmed

Bug description:
  Description
  ===========
  Using virt-manager to create a VM in Aarch64, Ubuntu 16.04.
  Add scsi disk to the VM. After add four or more scsi disks, start the VM and will got Qemu error.

  Steps to reproduce
  ==================
  1.Use virt-manager to create a VM.
  2.After the VM is started, add scsi disk to the VM. They will be allocated to "sdb,sdc,sdd....." .
  3.If we got a disk name > sdg, virt-manager will also assign a virtio-scsi controller for this disk.And the VM will be shutdown.
  4.Start the VM, will see the error log.

  
  Expected result
  ===============
  Start the vm smoothly.The added disks can work.

  Actual result
  =============
  Got the error:
  starting domain: internal error: process exited while connecting to monitor: qemu-system-aarch64: /build/qemu-zxCwKP/qemu-2.5+dfsg/migration/savevm.c:620: vmstate_register_with_alias_id: Assertion `!se->compat || se->instance_id == 0' failed.
  details=Traceback (most recent call last):
    File "/usr/share/virt-manager/virtManager/asyncjob.py", line 90, in cb_wrapper
      callback(asyncjob, *args, **kwargs)
    File "/usr/share/virt-manager/virtManager/asyncjob.py", line 126, in tmpcb
      callback(*args, **kwargs)
    File "/usr/share/virt-manager/virtManager/libvirtobject.py", line 83, in newfn
      ret = fn(self, *args, **kwargs)
    File "/usr/share/virt-manager/virtManager/domain.py", line 1402, in startup
      self._backend.create()
    File "/usr/local/lib/python2.7/dist-packages/libvirt.py", line 1035, in create
      if ret == -1: raise libvirtError ('virDomainCreate() failed', dom=self)
  libvirtError: internal error: process exited while connecting to monitor: qemu-system-aarch64: /build/qemu-zxCwKP/qemu-2.5+dfsg/migration/savevm.c:620: vmstate_register_with_alias_id: Assertion `!se->compat || se->instance_id == 0' failed.

  
  Environment
  ===========
  1. virt-manager version is 1.3.2

  2. Which hypervisor did you use?
      Libvirt+KVM
      $ kvm --version
      QEMU emulator version 2.5.0 (Debian 1:2.5+dfsg-5ubuntu10.1), Copyright (c) 2003-2008 Fabrice Bellard
      $ libvirtd --version
      libvirtd (libvirt) 1.3.1

  3. Which storage type did you use?
     In the host file system,all in one physics machine.
  stack@u202154:/opt/stack/nova$ df -hl
  Filesystem Size Used Avail Use% Mounted on
  udev 7.8G 0 7.8G 0% /dev
  tmpfs 1.6G 61M 1.6G 4% /run
  /dev/sda2 917G 41G 830G 5% /
  tmpfs 7.9G 0 7.9G 0% /dev/shm
  tmpfs 5.0M 0 5.0M 0% /run/lock
  tmpfs 7.9G 0 7.9G 0% /sys/fs/cgroup
  /dev/sda1 511M 888K 511M 1% /boot/efi
  cgmfs 100K 0 100K 0% /run/cgmanager/fs
  tmpfs 1.6G 0 1.6G 0% /run/user/1002
  tmpfs 1.6G 0 1.6G 0% /run/user/1000
  tmpfs 1.6G 0 1.6G 0% /run/user/0

  4. Environment information:
     Architecture : AARCH64
     OS: Ubuntu 16.04

  The Qemu commmand of libvirt is :
  2016-06-20 02:39:46.561+0000: starting up libvirt version: 1.3.1, package: 1ubuntu10 (William Grant <wgrant@ubuntu.com> Fri, 15 Apr 2016 12:08:21 +1000), qemu version: 2.5.0 (Debian 1:2.5+dfsg-5ubuntu10.1), hostname: u202154
  LC_ALL=C PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin QEMU_AUDIO_DRV=none /usr/bin/kvm -name cent7 -S -machine virt,accel=kvm,usb=off -cpu host -drive file=/usr/share/edk2.git/aarch64/QEMU_EFI-pflash.raw,if=pflash,format=raw,unit=0,readonly=on -drive file=/var/lib/libvirt/qemu/nvram/cent7_VARS.fd,if=pflash,format=raw,unit=1 -m 2048 -realtime mlock=off -smp 2,sockets=2,cores=1,threads=1 -uuid d5462bb6-159e-4dbd-9266-bf8c07fa1695 -nographic -no-user-config -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/domain-cent7/monitor.sock,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown -boot strict=on -device i82801b11-bridge,id=pci.1,bus=pcie.0,addr=0x1 -device pci-bridge,chassis_nr=2,id=pci.2,bus=pci.1,addr=0x1 -device virtio-scsi-device,id=scsi0 -device lsi,id=scsi1 -device lsi,id=scsi2 -device virtio-scsi-device,id=scsi3 -usb -drive file=/var/lib/libvirt/images/cent7-2.img,format=qcow2,if=none,id=drive-scsi0-0-0-0 -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 -drive if=none,id=drive-scsi0-0-0-1,readonly=on -device scsi-cd,bus=scsi0.0,channel=0,scsi-id=0,lun=1,drive=drive-scsi0-0-0-1,id=scsi0-0-0-1 -drive file=/var/lib/libvirt/images/cent7-10.img,format=qcow2,if=none,id=drive-scsi0-0-0-2 -device scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,lun=2,drive=drive-scsi0-0-0-2,id=scsi0-0-0-2 -drive file=/var/lib/libvirt/images/cent7-11.img,format=qcow2,if=none,id=drive-scsi0-0-0-3 -device scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,lun=3,drive=drive-scsi0-0-0-3,id=scsi0-0-0-3 -drive file=/var/lib/libvirt/images/cent7-13.img,format=qcow2,if=none,id=drive-scsi3-0-0-0 -device scsi-hd,bus=scsi3.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi3-0-0-0,id=scsi3-0-0-0 -netdev tap,fd=33,id=hostnet0,vhost=on,vhostfd=35 -device virtio-net-device,netdev=hostnet0,id=net0,mac=52:54:00:a1:6e:75 -serial pty -msg timestamp=on
  Domain id=11 is tainted: host-cpu

  The libvirt xml is:
  <domain type='kvm'>
    <name>cent7</name>
    <uuid>d5462bb6-159e-4dbd-9266-bf8c07fa1695</uuid>
    <memory unit='KiB'>2097152</memory>
    <currentMemory unit='KiB'>2097152</currentMemory>
    <vcpu placement='static'>2</vcpu>
    <os>
      <type arch='aarch64' machine='virt'>hvm</type>
      <loader readonly='yes' type='pflash'>/usr/share/edk2.git/aarch64/QEMU_EFI-pflash.raw</loader>
      <nvram>/var/lib/libvirt/qemu/nvram/cent7_VARS.fd</nvram>
      <boot dev='hd'/>
    </os>
    <cpu mode='host-passthrough'/>
    <clock offset='utc'/>
    <on_poweroff>destroy</on_poweroff>
    <on_reboot>restart</on_reboot>
    <on_crash>restart</on_crash>
    <devices>
      <emulator>/usr/bin/kvm</emulator>
      <disk type='file' device='disk'>
        <driver name='qemu' type='qcow2'/>
        <source file='/var/lib/libvirt/images/cent7-2.img'/>
        <target dev='sda' bus='scsi'/>
        <address type='drive' controller='0' bus='0' target='0' unit='0'/>
      </disk>
      <disk type='file' device='cdrom'>
        <driver name='qemu' type='raw'/>
        <target dev='sdb' bus='scsi'/>
        <readonly/>
        <address type='drive' controller='0' bus='0' target='0' unit='1'/>
      </disk>
      <disk type='file' device='disk'>
        <driver name='qemu' type='qcow2'/>
        <source file='/var/lib/libvirt/images/cent7-10.img'/>
        <target dev='sdc' bus='scsi'/>
        <address type='drive' controller='0' bus='0' target='0' unit='2'/>
      </disk>
      <disk type='file' device='disk'>
        <driver name='qemu' type='qcow2'/>
        <source file='/var/lib/libvirt/images/cent7-11.img'/>
        <target dev='sdd' bus='scsi'/>
        <address type='drive' controller='0' bus='0' target='0' unit='3'/>
      </disk>
      <disk type='file' device='disk'>
        <driver name='qemu' type='qcow2'/>
        <source file='/var/lib/libvirt/images/cent7-13.img'/>
        <target dev='sdv' bus='scsi'/>
        <address type='drive' controller='3' bus='0' target='0' unit='0'/>
      </disk>
      <controller type='scsi' index='0' model='virtio-scsi'>
        <address type='virtio-mmio'/>
      </controller>
      <controller type='scsi' index='1'>
        <address type='virtio-mmio'/>
      </controller>
      <controller type='scsi' index='2'>
        <address type='virtio-mmio'/>
      </controller>
      <controller type='scsi' index='3' model='virtio-scsi'>
        <address type='virtio-mmio'/>
      </controller>
      <controller type='pci' index='0' model='pcie-root'/>
      <controller type='pci' index='1' model='dmi-to-pci-bridge'>
        <model name='i82801b11-bridge'/>
        <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0'/>
      </controller>
      <controller type='pci' index='2' model='pci-bridge'>
        <model name='pci-bridge'/>
        <target chassisNr='2'/>
        <address type='pci' domain='0x0000' bus='0x01' slot='0x01' function='0x0'/>
      </controller>
      <interface type='bridge'>
        <mac address='52:54:00:a1:6e:75'/>
        <source bridge='br0'/>
        <model type='virtio'/>
        <address type='virtio-mmio'/>
      </interface>
      <serial type='pty'>
        <target port='0'/>
      </serial>
      <console type='pty'>
        <target type='serial' port='0'/>
      </console>
    </devices>
  </domain>

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