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I tried to start a Windows VM using QEMU/KVM (and virt-manager) on Ubuntu 16.04, it worked perfectly before I upgraded the qemu version from 2.5 to 3.0 (I followed this to build and install qemu3.0).

After installing qemu3.0, I encountered some problems:

Firstly,

Cannot check QEMU binary /usr/bin/qemu-system-x86_64

So I made a symbol link like this ln -s /usr/local/bin/qemu-system-x86_64 /usr/bin/qemu-system-x86_64, fixed.

Secondly,

Cannot check QEMU binary /usr/bin/qemu-kvm: No such file or directory

So I modified the vm's config file like this:

                   qemu-kvm (original) 
<emulator>/usr/bin/qemu-system-x86_64</emulator> 

Fixed, but I still can't start the VM,

Unable to complete install: 'internal error: early end of file from monitor, possible problem: 2019-10-18T01:50:27.678306Z qemu-system-x86_64: -chardev pty,id=charserial0: char device redirected to /dev/pts/1 (label charserial0) 2019-10-18T01:50:27.683198Z qemu-system-x86_64: Property '.md-clear' not found'

I deleted the VM and created again, the same error message appeared while creating. I have no idea how to solve this problem, what steps am I missing? Or any wrong configurations ?

Here is the ENV:

$ lsb_release -a
Distributor ID: Ubuntu
Description:    Ubuntu 16.04.5 LTS
Release:    16.04
Codename:   xenial

$ which qemu-system-x86_64  
/usr/bin/qemu-system-x86_64

$ qemu-system-x86_64 --version
QEMU emulator version 3.0.0

$ libvirtd --version
libvirtd (libvirt) 1.3.1

$ uname -r
4.4.0-159-generic

$ egrep -c '(vmx|svm)' /proc/cpuinfo
32

Update:
I reinstall qemu to the path /usr/bin, still have the same problem and same error message.

Update 2019/10/24:
I can create a new vm by using virt-install command line, avoid virt-manager using md-clear as a cpu parameter, I am not sure this way is correct, but it just solved the problem temporarily.

virt-install --virt-type kvm \
  --machine=pc \
  --name winserver2016 \
  --ram 8192 \
  --disk /home/rd/corey/50G-Volume.img \
  --network network=default \
  --noautoconsole \
  --os-type=windows \
  --cdrom=/home/rd/corey/winserver.iso
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    This is a cpu feature related to spectre and such vulnerabilities. It might be that due to the version mismatches it now asks qemu to use it but it doesn't know how to handle it correctly? You could check the cmdline in /var/log/libvirt/qemu/<guestname>.log - is there a mentioning of md-clear? And if so does your self built qemu know it, check qemu-system-x86 -cpu ? Oct 21, 2019 at 8:09
  • Thanks for your reply @ChristianEhrhardt, I can find the error message in /var/log/libvirt/qemu/<guestname>.log, it shows qemu-system-x86_64: Property '.md-clear' not found and -cpu SandyBridge-IBRS,+ssbd,+md-clear.......
    – Corey
    Oct 24, 2019 at 1:31
  • Then, I check qemu-system-x86_64 --machine pc -cpu help, I can't find md-clear in the list, does it mean that this cpu cannot support md-clear feature?
    – Corey
    Oct 24, 2019 at 1:33

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