Re: [Qemu-devel] [PULL 26/28] apic: Use apic_id as apic's migration instance_id

[Igor Mammedov <imammedo@redhat.com>]

On Tue, 26 Jul 2016 10:41:38 +0530
Amit Shah <amit.shah@redhat.com> wrote:

> On (Wed) 20 Jul 2016 [12:08:32], Eduardo Habkost wrote:
> > From: Igor Mammedov <imammedo@redhat.com>
> > 
> > instance_id is generated by last_used_id + 1 for a given device type
> > so for QEMU with 3 CPUs instance_id for APICs is a seti of [0, 1, 2]
> > When CPU in the middle is hot-removed and migration started
> > APICs with instance_ids 0 and 2 are transferred in migration stream.
> > However target starts with 2 CPUs and APICs' instance_ids are
> > generated from scratch [0, 1] hence migration fails with error
> >   Unknown savevm section or instance 'apic' 2
> > 
> > Fix issue by manually registering APIC's vmsd with apic_id as
> > instance_id, in this case instance_id on target will always
> > match instance_id on source as apic_id is the same for a given
> > cpu instance.
> > 
> > Reported-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> > Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>  
> 
> After these patches, the static checker complains about missing
> sections:
> 
> Section "apic-common" does not exist in dest
> Section "apic" does not exist in dest
> Section "kvm-apic" does not exist in dest
> 
> This will break migration from older versions.
Still can't reproduce:
here is my CLI on SRC:
  qemu-system-x86_64-v2.6.0  \
   -snapshot -enable-kvm -smp 6,maxcpus=6 -m 256M rhel72.img -monitor stdio -M pc-i440fx-2.6 -nodefaults

monitor# stop
monitor# migrate "exec:gzip -c > STATEFILE.gz"
^C

CLI on DST:
  qemu-system-x86_64-v2.7.0-rc0 \
   -snapshot -enable-kvm -smp 6,maxcpus=6 -m 256M rhel72.img -monitor stdio -M pc-i440fx-2.6 -nodefaults -incoming "exec: gzip -c -d STATEFILE.gz"

But I've found issue with I2C, which breaks migration for me with:

(qemu) qemu-system-x86_64: Missing section footer for i2c_bus
qemu-system-x86_64: load of migration failed: Invalid argument

Which is bisects to:

commit 2293c27faddf9547dd8b52423caa6e85844eec3a
Author: KONRAD Frederic <fred.konrad@greensocs.com>
Date:   Tue Jun 14 15:59:14 2016 +0100

    i2c: implement broadcast write

hacking migration hunks of it to old VMState fixes I2C issue,
and no apic related issues are noticed.

> 
> 		Amit
>