[Xen-devel] live migrating hvm from 4.4 to 4.5 fails due to kvmvapic

[Olaf Hering <olaf@xxxxxxxxx>]

Migrating a HVM guest from staging-4.4 to staging-4.5 fails:

# cat /var/log/xen/qemu-dm-fv-x64-sles12sp1-clean--incoming.log
char device redirected to /dev/pts/4 (label serial0)
xen_ram_alloc: do not alloc f800000 bytes of ram at 0 when runstate is INMIGRATE
xen_ram_alloc: do not alloc 800000 bytes of ram at f800000 when runstate is 
INMIGRATE
xen_ram_alloc: do not alloc 10000 bytes of ram at 10000000 when runstate is 
INMIGRATE
xen_ram_alloc: do not alloc 40000 bytes of ram at 10010000 when runstate is 
INMIGRATE
Unknown savevm section or instance 'kvm-tpr-opt' 0
qemu-system-i386: load of migration failed: Invalid argument


Initially I thought we broke our sles12 xen, but for some reason xen.git fails
in the very same way. In 4.4 kvmvapic gets enabled, it gets migrated in the
"kvm-tpr-opt" VMStateDescription. The 4.5 qemu does not know about it because
'kvmvapic' is not enabled. As a result the entire savevm stream is rejected.

One thing to fix it in staging-4.5 is to introduce a dummy device which
handles a section named "kvm-tpr-opt". I already have a hack which does
that, and the migration proceeds. I will propose a patch to deal with
this part of the bug.

Unfortunately later the VM appears to be alive, but nothing happens in
it. I assume it gets no further interrupts. Guess I need help with this
part of the bug.


domU.cfg looks like this:

name="x"
memory=256
serial="pty"
builder="hvm"
boot="cd"
disk=[
        'file:/disk0.raw,hda,w',
        'file:/some.iso,hdc:cdrom,r',
]
vif=[
        'bridge=br0'
]
keymap="de"
vfb = [
        'type=vnc,vncunused=1,keymap=de'
]
usb=1
usbdevice='tablet'


Olaf

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