[Bug 1856834] Re: PCI broken in qemu ppc e500 in v2.12.0 and other versions

[ecsdn <1856834@bugs.launchpad.net>]

Thanks for all the help Laurent! I'm new to git so not surre how to
'properly' revert a previous commit on top of master, so I'll google,
but if you have some a good link please do send.

Also, I've heard of the term "bisect" for figuring out at which commit
something breaks and if there were some good documentation to spell out
the steps to do that for users that aren't, well advanced kernel gurus
:D , I'm sure we'd be happy to save you smarter guys time with any
mundane testing steps when possible :) thx!

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https://bugs.launchpad.net/bugs/1856834

Title:
  PCI broken in qemu ppc e500 in v2.12.0 and other versions

Status in QEMU:
  New

Bug description:
  The same qemu -M mpc... command that works on qemu-system-ppc version
  2.8.0 freezes guest on bootup and shows error for qemu-system-ppc
  version 4.2.0release and 4.19dirtygit:

  qemu-system-ppc: virtio-blk failed to set guest notifier (-24), ensure -accel kvm is set.
  qemu-system-ppc: virtio_bus_start_ioeventfd: failed. Fallback to userspace (slower).

  ends/freezes at:
  nbd: registered device at major 43
   vda:

  I'm using -drive file=/home/me/rawimage.dd,if=virtio and works fine in
  version 2.8.0 installed with apt-get install (Ubuntu 17.04) and also
  with 2.8.0 official release from git/github that I compiled/built
  myself. But both of the newer releases fail on the same exact machine
  same config.

  I also noticed that qemu-2.8.0 was fine with mtd but the newer ones I tried weren't, ie gave
  qemu-system-ppc: -drive if=mtd: machine type does not support if=mtd,bus=0,unit=0
  (but I removed -drive if=mtd since wasn't using it anyway)

  I also tried on windows but I think virtio doesn't work on windows
  hosts at all? On windows host it fails the same way, even version 2.12
  as well as 4.1.10...

  used:
  ./configure --prefix=/opt/... --enable-fdt --enable-kvm --enable-debug

  (basically all steps the same on same exact system same config, yet
  2.8.0 works fine whether apt-get installed or built from source while
  the others I built, 4.19/4.2.0 or 2.12/4.1.10(win) don't.)

  In case newer qemu versions act weird on various kernels, I did try with both vmlinuz-4.10.0-19-generic and vmlinuz-4.13.12-041312-generic (I didn't compile them but I can provide config-..files. This is on Ubuntu 17.04 x86_64 host emulating e500v2 cpm guest, ie -M mpc... GUEST kernel 2.6.32.44 which is why I can't use -M ppce500 instead..)
  tx
       ecs

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