[Qemu-devel] [Bug 899961] Re: qemu/kvm locks up when run 32bit userspace with 64bit kernel

[Michael Tokarev]

After some more digging I found out that qemu also has this very issue,
but it happens a bit differently.  In particular, this very same winXP
test guest freezes in upstream qemu with -enable-kvm on _shutdown_, not
on restart.  In qemu-kvm it happens on restart but not on shutdown.

And bisecting plain qemu leads to this commit:

commit 12d4536f7d911b6d87a766ad7300482ea663cea2
Author: Anthony Liguori <address@hidden>
Date:   Mon Aug 22 08:24:58 2011 -0500

    main: force enabling of I/O thread
    
As far as I remember, qemu-kvm always had iothread enabled, that's why the bug 
initially was only reproducible on qemu-kvm.

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https://bugs.launchpad.net/bugs/899961

Title:
  qemu/kvm locks up when run 32bit userspace with 64bit kernel

Status in QEMU:
  New
Status in “qemu-kvm” package in Debian:
  Confirmed

Bug description:
  Only applies to qemu-kvm 1.0, and only when kernel is 64bit and
  userspace is 32bit, on x86.  Did not happen with previous released
  versions, such as 0.15.  Not all guests triggers this issue - so far,
  only (32bit) windows 7 guest shows it, but does that quite reliable:
  first boot of an old guest with new qemu-kvm, windows finds a new CPU
  and suggests rebooting - hit "Reboot" and in a few seconds it will be
  locked up (including the monitor), with no CPU usage whatsoever.
  Killable only with -9.

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