Bringing this topic up - again - as I am still having issues (Virtualbox issues)
Have a Win10 VM, and multiple Linux distros for testing etc, and all have been on VirtualBox, Tumbleweed as the host, up until now (as per the previous post), but after having seen an article (https://tinyurl.com/2bhg8wql), thought I would give Virt-Manager/KVM a go.
So today (about 4 hours ago), ran up a new Virtual machine, using this new pairing. Came back recently, after the PC had been sitting for an hour or so, and, yes, same issue - PC was locked up, mouse moving VERY sporadically, unable to accurately click on anythingā¦
After about 10 mins, I actually managed to kill the VM using Ctrl-Alt-esc, and most things came back, although my Vivaldi browser didnāt - had to kill/restart.
Over time, this had happened on multiple Dell PCs (several Optiplex 9020s, 7060, etc)currently on a Lenovo M920S, etc. Generally with 16GB RAM (generally only give a VM 4GB), plenty of HDD space (the virtual machines are on an SSD), and no issues running them āin generalā, mostly, but not always, it is when they have sat for a while (and doing nothingā¦)
One gotcha I will try shortly, is to run one up from scratch, as I DID cheat with the current one - used an existing Linux Mint disk from VirtualBox. It has all the latest updates etcā¦
Helpā¦??
At first, congratulations on dropping litterbox and welcome in KVM users community! 
How did you setup devices (eg. sata emulation or Virtio)?
If Virtio, did you install necessary drivers?
How did you setup Windows power management? (is plenty of articles in Internet how to adjust it for virtualization)
What Windows Event Viewer shows at the time when the problem appears?
Hint: In yours previous post you mentioned allocating 1 core to VM. Try different approach and allocate 2 cores but restrict them to use, lets say, 60% of each core by using cpulimit=1.2.
Thanks for the reply.
Have to sort out the different terminology for KVMā¦
Disk is shown as VirtIO Disk1. How do I setup the drivers? (assuming their is a Webpage somewheres, where all this info is??)
āWindows power managementā?? Not using Windows - Tumbleweedā¦
Have added another core, but not sure where I limit to 60%?
Thanks.
Please be aware of where KVM drops the VM images by default and, the SELinux needs if your ā/varā partition isnāt large enough ā
# LANG=C semanage fcontext -C -l
SELinux fcontext type Context
/home01 all files system_u:object_r:home_root_t:s0
/home01/KVM all files system_u:object_r:virt_var_lib_t:s0
SELinux Local fcontext Equivalence
.
.
/home01/KVM/images = /var/lib/libvirt/images
#
An explanation is in the SELinux āsemanage-fcontextā man page:
For home directories under top level directory, for example /disk6/home, execute the following commands. # semanage fcontext -a -t home_root_t "/disk6" # semanage fcontext -a -e /home /disk6/home # restorecon -R -v /disk6
@michu_l
Thanks for the reply.
Have to sort out the different terminology for KVMā¦
Disk is shown as VirtIO Disk1. How do I setup the drivers? (assuming their is a Webpage somewheres, where all this info is??)
āWindows power managementā?? Not using Windows - Tumbleweedā¦
Have added another core, but not sure where I limit to 60%?
Thanks.
Going away for a couple of weeks - will get back to itā¦
This is correct - in most cases the most efficient way to go.
Did you follow any migration guide or did you just copy the images?
Please see below link to the Virtio drivers. Probably the most convenient way is to download iso and use it with any VM when required.
https://github.com/virtio-win/virtio-win-pkg-scripts/blob/master/README.md
Of course you donāt but you use Windows inside virtual machine. You still have to administrate this virtual computer and the best way, to check what is wrong with it, is to check itās logs. You are going to use tools inside yourās VMs adequate to operating systems on them.
The rule of thumb for VMs is to disable itās power management and let the host (hypervisor) to handle it all.
In addition the bare minimum for smooth communication host-guest is to install qemu guest tools (for KVM/QEMU, in case of other hypervisors itās going to be different software tools. Itās bassicaly VirtualBox Guest Additions equivalent - Youāve used so you know).
BTW. You will find qemu guest tools on the iso above. Probably worth to mention you should install those tools on every VM guest no matter what OS is used on them. Keep that iso and check for updates regularly (I mean twice a year).
By adding to this VM settings cpulimit=1.2. Apologies, Iāve assumed there is an option in GUI. In case of GUI applications I donāt know how to setup it. Iāll check cockpit later, just because I wonder if there is an option.
Enjoy your holidays.
Another thought. Before you start messing with your existing VMs I would suggest clean install and exercise installing all the drivers and proper settings. At the same time you can test different setting and chose what works best for you. Then backup of the VM or at least snapshot and only then āfixingā it (Iām suspecting lack of correct drivers and misconfiguration). It may appear to be easier just to migrate your data and soft to the new, freshly installed OS.
Good luck.
Initially, just pointed it at the current VB diskā¦
Have since done a āfrom scratchā install.
Are those drivers just for Windows? Yes, I will be using Win as a virtual machine, but so far, have only copied/run up a Mint image.
I am assuming you are meaning within the View>Details>XML section, where this, for example, info is:
</features>
<cpu mode="host-passthrough" check="none" migratable="on"/>
<clock offset="utc">
<timer name="rtc" tickpolicy="catchup"/>
<timer name="pit" tickpolicy="delay"/>
<timer name="hpet" present="no"/>
</clock>
This is where I am at the momentā¦
Now, DEFINITELY going on holsā¦ 
They are for both, Windowsa and Linux. Most of the recent distros have them in their repos. Some of them can even recognize they are installed in the virtual environment and install qemu-guest-agent automatically. Unfortunately not all of them so itās worth to make sure itās installed.
Yes and no.
Iāve mixed-up this setting with Proxmox - it has KVM under the hood, and I assumed KVM handles this directly but itās not a case.
But because Virtual Machine Manager has libvirt under the hood, so Iām pretty sure combination of <period> and <quota> in XML will do the trick.
There is also an option to use command cpulimit on the host but itās not going to be permanent - unless you will run script or find other way to automate it.
https://libvirt.org/formatdomain.html#cpu-tuning
https://linuxcommandlibrary.com/man/cpulimit
Back from holsā¦
About 5,300km on the bike - think I blew the cobwebs out!
But back to the taskā¦
Fired up my Mint yesterday, and it ran all day, without a hiccup - so impressed!
But on to the main task - rebirth the Windows Virtualbox disk I have, for QEMU, so far without joyā¦
Cannot get it to boot:
Initially, tried attaching as a standard VB disk (how do I do a COPY in the running console?)
and basically get
BdsDxe: No bootable option or device was found.
BdsDxe: Press any key to enter the Boot Manager Menu.
which gives:
and selecting EFI Firmware Setup, gives:
Canāt seem to get into configure anythingā¦? There is only 1 disk, and no option to change flags/partitions whateverā¦
Have also created a qcow2 image from the vdi (qemu-img convert -f vdi -O qcow2 Windows10_1.vdi Windows10.qcow2), and this gives the same result. both images are about 50gbā¦
How to go about getting something to boot?
When I initially added the existing VB Mint disk, it just workedā¦
Thanks.
Might give up on Virtual Machinesā¦ 
After posting the above, closed that machine, opened my NEW (ie created in QEMU, not the transferred one) Mint and started playing, within 2 minutes my host had locked up with 100% disk usage, very little movement in mouse pointer, no response from keyboard/mouse clicksā¦ Gave it about 10 mins, only option was to do a hard reboot.
trying it againā¦
On reboot, so far working fine, but this is what p#sses me off! Totally unpredictable (I thinkā¦)
It does not boot because lack of the virtio-scsi driver (normally itās installed during Windows installation, F6 and pointing to the ISO mentioned before).
To fix it, temporarily, switch disk type from virtio to sata (VM will boot and work but itās not the most efficient way). Once it boots, install drivers from ISO. Shutdown VM, switch back to virtio, and it will boot.
Any clues in host logs/journal?
I believe it is already using sata??
Have not connected this image before, and this is the config it comes up with?
Thanks.
First problem overcomeā¦ = my stupidity!!
Have been using uefi on my machines for yonks(?), but my Win VM was originally installed in the days of Win8, and has been upgraded (reinstalled at times, but into the same machine, so always came up licencedā¦), and, of course, on moving this across to QEMU, it has assumed UEFI, and I havenāt even thought about it, so re-adding the disk, but setting it to BIOS, has workedā¦ to a point.
Now I am going round in circles with the āPreparing Automatic Repairā, that obviously doesnāt want to fix itā¦
Have been attempting this with the VDI disk image, will try a cow conversionā¦
Thanks.
Anyway, back to original problemā¦
Have now switched apps to QEMU (uninstalled VirtualBox), but still have the issue where it is locking my PC (sometimes totally/instantaneous) and the only way out is a hard reset.
Happened this morning - have a Windows10 guest, has been working OK, went to start this morning, and about 5 seconds after pressing the run button, the whole PC frozeā¦
Question: could this be tied to a specific app - after this, started it again, and it seemed to be working OK, then noticed it start to hesitate. Was mostly using Vivaldi browser, and Thunderbird. While I still could (normally it is too quick, and I cantā¦), I killed Vivaldi. PC āseemedā to fix itself, and continued with session. Would it make sense that Vivaldi is causing the prob? Is there any way that I could chase this down?
Thanks.
@hornetster look at the logs with journalctl how much system memory and cpu cores, how much allocated to the VM?
CPUs:
Host: Logical host CPUs = 6
vCPU Allocation = 2
Memory
Host: 16GB
Guest: 4GB
Disk:
Generally 35-40gb/guest, dynamic.
Always have trouble deciphering anything in journalctlā¦ 
Just had it lock up on me, these were the last few minutes of journalctl.
Seem to be a couple of things in there, but I canāt decipher.
ie:
Mar 11 20:46:49 boss kwin_wayland[9407]: Libinput: client bug: timer button-debounce-debounce-event1: scheduled expiry is in the past (-449ms), your system is too slow
Mar 11 20:46:51 boss kwin_wayland[9407]: Libinput: client bug: timer button-debounce-debounce-event1: scheduled expiry is in the past (-43ms), your system is too slow
Text from journalctl:
journalctl text
Thanks.
So all is good without the browser running?
Are you connecting to the virtual machine with the manager or client?
Your user is in the libvirt group?
Yes
Iām on the host, using Virtual Machine Manager
Not 100% sureā¦ Sometimes works fine with, if I close it down, may be OKā¦
Can anyone test??
Not 100% one way or the otherā¦