Re: [Qemu-devel] Bug#922612: qemu-system: black screen when guest goes to powersave, does not come back

Re: [Qemu-devel] Bug#922612: qemu-system: black screen when guest goes to powersave, does not come back

[Michael Tokarev]

Forwarding from Debian bugreport http://bugs.debian.org/922612

18.02.2019 15:43, Marc Lehmann wrote:
> Package: qemu-system
> Version: 1:3.1+dfsg-4
> Severity: normal
> 
> Dear Maintainer,
> 
> after upgrading to qemu 3.1 from stretch [from qemu 2.8 -- mjt], I found
> that both linux and windows guests, when using the qxl device, do not
> come back from deep power save.
> 
> That is, when I run either a standard ubuntu 17.10 or windows 10 (with
> qxl-dod driver), then by default they switch off the screen after a while,
> which results in black screen in qemu, as expected.
> 
> If one moves the mouse or presses a key shortly after this, the screen comes back.
> 
> If I let the systems idle for longer (say, half an hour), then they seem
> to go into a deeper powersave, and pressing a key or moving the mouse does
> NOT restore the screen - it stays black.
> 
> When the vm is in this state, I have not found a way to get the display
> back, the only way that works is to quit qemu and start it again (meaning
> boot the guest again in a new qemu instance, I have not tried to
> suspend/resume a vm).
> 
> I have verified that mouse inputs and keypresses are registered correctly
> by the guest in this state, so I assume it does try to switch on the
> virtual monitor.
> 
> Since this happens with both linux and windows guests, this looks like a
> bug in qemu's display code to me.

Thanks,

/mjt

Re: [Qemu-devel] Bug#922612: qemu-system: black screen when guest goes to powersave, does not come back

[Gerd Hoffmann]

  Hi,

> > That is, when I run either a standard ubuntu 17.10 or windows 10 (with
> > qxl-dod driver), then by default they switch off the screen after a while,
> > which results in black screen in qemu, as expected.

Just the screen saver I guess.

> > If I let the systems idle for longer (say, half an hour), then they seem
> > to go into a deeper powersave, and pressing a key or moving the mouse does
> > NOT restore the screen - it stays black.

Probably "systemctl suspend".

> > When the vm is in this state, I have not found a way to get the display
> > back, the only way that works is to quit qemu and start it again (meaning
> > boot the guest again in a new qemu instance, I have not tried to
> > suspend/resume a vm).
> > 
> > I have verified that mouse inputs and keypresses are registered correctly
> > by the guest in this state, so I assume it does try to switch on the
> > virtual monitor.

Doesn't reproduce.

Can you log into the machine (serial console, network)?
If so: anything suspicious in the kernel log?

Also: it is possible to disable suspend support (libvirt xml):

  <pm>
    <suspend-to-mem enabled='no'/>
    <suspend-to-disk enabled='no'/>
  </pm>

Suspending virtual machines typically adds little benefit and isn't
tested that well, so I'd recommend doing that.

Bugs can be in both host (qemu) and guest (linux kernel driver).   Often
it is quite difficult to debug and to figure who is actually at fault
here.

cheers,
  Gerd