Same issue (windows vm) here on my running 5.1 version.
According to the previous posts, I have changed the grub to starting up the older kernel version 4.10.17-4.
Unfortunaltely, no VM are able to start. I have checked also the kernel 4.10.17-3. Same behavior for this kernel.... no vm can start.
Here the output while trying to startup the vm:
root@pve02:~# pveversion
pve-manager/5.1-35/722cc488 (running kernel: 4.10.17-3-pve)
root@pve02:~#
root@pve02:~# qm start 201
kvm: -drive file=/dev/zvol/local-zfs/vm-201-disk-1,if=none,id=drive-scsi0,format=raw,cache=none,aio=native,detect-zeroes=on: Could not open '/dev/zvol/local-zfs/vm-201-disk-1': No such file or directory
start failed: command '/usr/bin/kvm -id 201 -chardev 'socket,id=qmp,path=/var/run/qemu-server/201.qmp,server,nowait' -mon 'chardev=qmp,mode=control' -pidfile /var/run/qemu-server/201.pid -daemonize -smbios 'type=1,uuid=a438095f-d567-403f-97d5-f1a555a9c7b9' -name DEB-WEB-02 -smp '1,sockets=1,cores=1,maxcpus=1' -nodefaults -boot 'menu=on,strict=on,reboot-timeout=1000,splash=/usr/share/qemu-server/bootsplash.jpg' -vga std -vnc unix:/var/run/qemu-server/201.vnc,x509,password -cpu kvm64,+lahf_lm,+sep,+kvm_pv_unhalt,+kvm_pv_eoi,enforce -m 2048 -k de-ch -device 'pci-bridge,id=pci.1,chassis_nr=1,bus=pci.0,addr=0x1e' -device 'pci-bridge,id=pci.2,chassis_nr=2,bus=pci.0,addr=0x1f' -device 'piix3-usb-uhci,id=uhci,bus=pci.0,addr=0x1.0x2' -device 'usb-tablet,id=tablet,bus=uhci.0,port=1' -chardev 'socket,path=/var/run/qemu-server/201.qga,server,nowait,id=qga0' -device 'virtio-serial,id=qga0,bus=pci.0,addr=0x8' -device 'virtserialport,chardev=qga0,name=org.qemu.guest_agent.0' -device 'virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3' -iscsi 'initiator-name=iqn.1993-08.org.debian:01:fb2dca598c9e' -drive 'if=none,id=drive-ide2,media=cdrom,aio=threads' -device 'ide-cd,bus=ide.1,unit=0,drive=drive-ide2,id=ide2,bootindex=200' -device 'virtio-scsi-pci,id=scsihw0,bus=pci.0,addr=0x5' -drive 'file=/dev/zvol/local-zfs/vm-201-disk-1,if=none,id=drive-scsi0,format=raw,cache=none,aio=native,detect-zeroes=on' -device 'scsi-hd,bus=scsihw0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0,id=scsi0,bootindex=100' -netdev 'type=tap,id=net0,ifname=tap201i0,script=/var/lib/qemu-server/pve-bridge,downscript=/var/lib/qemu-server/pve-bridgedown,vhost=on' -device 'virtio-net-pci,mac=32:03:1B:56:AA:7D,netdev=net0,bus=pci.0,addr=0x12,id=net0,bootindex=300'' failed: exit code 1
root@pve02:~#
Any help are welcome
Cheers