[Qemu-devel] [Bug 1580459] Re: Windows (10?) guest freezes entire host on shutdown if using PCI passthrough

[jimrif <jimrif@gmail.com>]

I'm not really sure what the other similar bug was, but what I was
experiencing was a Win10 VM locking up the host machine upon shutdown of
the VM after several minutes of gaming (or even several hours of
youtube/netflix).  It didn't happen all of the time, but most of the
time after the VM had be up for a while.

I am positive that recompiling without SND support is when the host
stopped crashing upon shutdown of the Windows 10 VM as I was only doing
one change at a time.  I had the issue for many months before removing
CONFIG_SND.  Since then, 2 months ago, I've upgraded qemu, libvirt, the
kernel and win10 updates, including the nVidia drivers.  I'm not really
wanting to compile SND back in as my server is also doing a lot more
than just hosting a Win10 VM and I don't want it to crash without anyone
else trying the fix.  If others try removing SND and continue to have
the issue, I will recompile to help troubleshoot but I am very confident
that is what stopped my system from locking up when shutting down a
Windows 10 VM.  If I were to take a guess, my guess is that just
removing snd-hda-intel would do the trick.

My hardware is a X99 board, i7-5820K, and a nVidia 980 graphics card
being passed through to the guest.  The host video card is a cheap 1x
radeon with HDMI sound.

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https://bugs.launchpad.net/bugs/1580459

Title:
  Windows (10?) guest freezes entire host on shutdown if using PCI
  passthrough

Status in libvirt:
  New
Status in QEMU:
  New
Status in Arch Linux:
  New
Status in Debian:
  New
Status in Fedora:
  New

Bug description:
  Problem: after leaving a Windows VM that uses PCI passthrough (as we
  do for gaming graphics cards, sound cards, and in my case, a USB card)
  running for some amount of time between 1 and 2 hours (it's not
  consistent with exactly how long), and for any amount of time longer
  than that, shutting down that guest will, right as it finishes
  shutting down, freeze the host computer, making it require a hard
  reboot. Unbinding (or in the other user's case, unbinding and THEN
  binding) any PCI device in sysfs, even one that has nothing to do with
  the VM, also has the same effect as shutting down the VM (if the VM
  has been running long enough). So, it's probably an issue related to
  unbinding and binding PCI devices.

  There's a lot of info on this problem over at https://bbs.archlinux.org/viewtopic.php?id=206050
  Here's a better-organized list of main details:
  -at least 2 confirmed victims of this bug; 2 (including me) have provided lots of info in the link
  -I'm on Arch Linux and the other one is on Gentoo (distro-nonspecific)
  -issue affects my Windows 10 guest and others' Windows guests, but not my Arch Linux guest (the others don't have non-Windows guests to test)
  -I'm using libvirt but the other user is not, so it's not an issue with libvirt
  -It seems to be version non-specific, too. I first noticed it at, or when testing versions still had the issue at (whichever version is lower), Linux 4.1 and qemu 2.4.0. It still persists in all releases of both since, including the newest ones.
  -I can't track down exactly what package downgrade can fix it, as downgrading further than Linux 4.1 and qemu 2.4.0 requires Herculean and system-destroying changes such as downgrading ncurses, meaning I don't know whether it's a bug in QEMU, the Linux kernel, or some weird seemingly unrelated thing.
  -According to the other user, "graphics intensive gameplay (GTA V) can cause the crash to happen sooner," as soon as "15 minutes"
  -Also, "bringing up a second passthrough VM with separate hardware will cause the same crash," and "bringing up another VM before the two-hour mark will not result in a crash," further cementing that it's triggered by the un/binding of PCI devices.
  -This is NOT related to the very similar bug that can be worked around by not passing through the HDMI device or sound card. Even when we removed all traces of any sort of sound card from the VM, it still had the same behavior.

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