[Bug 1882784] Re: Legacy IGD passthrough in QEMU 5 disabled

[Thomas Huth]

** Changed in: qemu
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1882784

Title:
  Legacy IGD passthrough in QEMU 5 disabled

Status in QEMU:
  Fix Released

Bug description:
  Bug with tag v5.0.0, or commit
  fdd76fecdde1ad444ff4deb7f1c4f7e4a1ef97d6

  As of QEMU 5 Legacy IGD PT is no longer working.

  Host is a Xeon E3-1226 v3 and my method to test is to run the
  following:

  ./qemu-system-x86_64 \
    -device 'pci-bridge,id=pci.1,chassis_nr=1,bus=pci.0,addr=0x1f' \
    -device 'vfio-pci,host=00:02.0,addr=02.0' \
    -L '/usr/share/kvm' \
    -nographic \
    -vga none \
    -nodefaults

  in the hope of seeing a "IGD device 0000:00:02.0 cannot support legacy
  mode due to existing devices at address 1f.0" error.

  The culprit appears to be this commit:

  https://github.com/qemu/qemu/commit/29d62771c81d8fd244a67c14a1d968c268d3fb19

  Specifically the following block in pci-quirks.c:

  #ifdef CONFIG_VFIO_IGD
      vfio_probe_igd_bar4_quirk(vdev, nr);
  #endif

  as the kconfig variable CONFIG_VFIO_IGD doesn't appear to be available
  outside of makefiles as described here:
  https://qemu.weilnetz.de/doc/devel/kconfig.html. I can confirm that
  the igd code is being pulled in as removing this check, as would
  defining the variable I presume, makes Legacy IGD PT work again (ie I
  see the expected "existing devices" error).

  I first spotted this in Proxmox, but have confirmed the bug by
  building QEMU sources.

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