[Bug 1869006] Re: PCIe cards passthrough to TCG guest works on 2GB of guest memory but fails on 4GB (vfio_dma_map invalid arg)

[Alex Williamson]

Summary: ARM64 TCG VM on x86 host has GPA overlapping host reserved IOVA
regions, vfio cannot map these.  The VM needs holes in the GPA to
account for this.  The 2nd and 3rd args of the vfio_dma_map error report
are the starting IOVA address and length respectively.

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https://bugs.launchpad.net/bugs/1869006

Title:
  PCIe cards passthrough to TCG guest works on 2GB of guest memory but
  fails on 4GB (vfio_dma_map invalid arg)

Status in QEMU:
  New

Bug description:
  During one meeting coworker asked "did someone tried to passthrough
  PCIe card to other arch guest?" and I decided to check it.

  Plugged SATA and USB3 controllers into spare slots on mainboard and
  started playing. On 1GB VM instance it worked (both cold- and hot-
  plugged). On 4GB one it did not:

  Błąd podczas uruchamiania domeny: internal error: process exited while 
connecting to monitor: 2020-03-25T13:43:39.107524Z qemu-system-aarch64: -device 
vfio-pci,host=0000:29:00.0,id=hostdev0,bus=pci.3,addr=0x0: VFIO_MAP_DMA: -22
  2020-03-25T13:43:39.107560Z qemu-system-aarch64: -device 
vfio-pci,host=0000:29:00.0,id=hostdev0,bus=pci.3,addr=0x0: vfio 0000:29:00.0: 
failed to setup container for group 28: memory listener initialization failed: 
Region mach-virt.ram: vfio_dma_map(0x563169753c80, 0x40000000, 0x100000000, 
0x7fb2a3e00000) = -22 (Invalid argument)

  Traceback (most recent call last):
    File "/usr/share/virt-manager/virtManager/asyncjob.py", line 75, in 
cb_wrapper
      callback(asyncjob, *args, **kwargs)
    File "/usr/share/virt-manager/virtManager/asyncjob.py", line 111, in tmpcb
      callback(*args, **kwargs)
    File "/usr/share/virt-manager/virtManager/object/libvirtobject.py", line 
66, in newfn
      ret = fn(self, *args, **kwargs)
    File "/usr/share/virt-manager/virtManager/object/domain.py", line 1279, in 
startup
      self._backend.create()
    File "/usr/lib64/python3.8/site-packages/libvirt.py", line 1234, in create
      if ret == -1: raise libvirtError ('virDomainCreate() failed', dom=self)
  libvirt.libvirtError: internal error: process exited while connecting to 
monitor: 2020-03-25T13:43:39.107524Z qemu-system-aarch64: -device 
vfio-pci,host=0000:29:00.0,id=hostdev0,bus=pci.3,addr=0x0: VFIO_MAP_DMA: -22
  2020-03-25T13:43:39.107560Z qemu-system-aarch64: -device 
vfio-pci,host=0000:29:00.0,id=hostdev0,bus=pci.3,addr=0x0: vfio 0000:29:00.0: 
failed to setup container for group 28: memory listener initialization failed: 
Region mach-virt.ram: vfio_dma_map(0x563169753c80, 0x40000000, 0x100000000, 
0x7fb2a3e00000) = -22 (Invalid argument)

  
  I played with memory and 3054 MB is maximum value possible to boot VM with 
coldplugged host PCIe cards.

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