[Qemu-devel] [Bug 1826422] Re: Regression: QEMU 4.0 hangs the host (*bisect included*)

[Saverio Miroddi <1826422@bugs.launchpad.net>]

> The change in QEMU 4.0 is only a change in defaults of the machine
type, it can be entirely reverted in the VM config with
kernel_irqchip=on or <ioapic driver='kvm'/> with libvirt. Using a
machine type prior to the q35 4.0 machine type would also avoid it.
There are no performance issues with these configurations that would
favor using 3.1 over 4.0.

Thanks for the detailed answer :-)

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https://bugs.launchpad.net/bugs/1826422

Title:
  Regression: QEMU 4.0 hangs the host (*bisect included*)

Status in QEMU:
  New

Bug description:
  The commit b2fc91db84470a78f8e93f5b5f913c17188792c8 seemingly
  introduced a regression on my system.

  When I start QEMU, the guest and the host hang (I need a hard reset to
  get back to a working system), before anything shows on the guest.

  I use QEMU with GPU passthrough (which worked perfectly until the
  commit above). This is the command I use:

  ```
  /path/to/qemu-system-x86_64
    -drive if=pflash,format=raw,readonly,file=/path/to/OVMF_CODE.fd
    -drive if=pflash,format=raw,file=/tmp/OVMF_VARS.fd.tmp
    -enable-kvm
    -machine q35,accel=kvm,mem-merge=off
    -cpu host,kvm=off,hv_vendor_id=vgaptrocks,hv_relaxed,hv_spinlocks=0x1fff,hv_vapic,hv_time
    -smp 4,cores=4,sockets=1,threads=1
    -m 10240
    -vga none
    -rtc base=localtime
    -serial none
    -parallel none
    -usb
    -device usb-tablet
    -device vfio-pci,host=01:00.0,multifunction=on
    -device vfio-pci,host=01:00.1
    -device usb-host,vendorid=<vid>,productid=<pid>
    -device usb-host,vendorid=<vid>,productid=<pid>
    -device usb-host,vendorid=<vid>,productid=<pid>
    -device usb-host,vendorid=<vid>,productid=<pid>
    -device usb-host,vendorid=<vid>,productid=<pid>
    -device usb-host,vendorid=<vid>,productid=<pid>
    -device virtio-scsi-pci,id=scsi
    -drive file=/path/to/guest.img,id=hdd1,format=qcow2,if=none,cache=writeback
    -device scsi-hd,drive=hdd1
    -net nic,model=virtio
    -net user,smb=/path/to/shared
  ```

  If I run QEMU without GPU passthrough, it runs fine.

  Some details about my system:

  - O/S: Mint 19.1 x86-64 (it's based on Ubuntu 18.04)
  - Kernel: 4.15
  - `configure` options: `--target-list=x86_64-softmmu --enable-gtk --enable-spice --audio-drv-list=pa`
  - EDK2 version: 1a734ed85fda71630c795832e6d24ea560caf739 (20/Apr/2019)
  - CPU: i7-6700k
  - Motherboard: ASRock Z170 Gaming-ITX/ac
  - VGA: Gigabyte GTX 960 Mini-ITX

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