Re: [Qemu-devel] [Qemu-ppc] [PATCH 0/4] spapr: disable hotplugging without OS

[Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>]

On 05/23/2017 02:52 PM, Daniel Henrique Barboza wrote:
> Hi Laurent,
>
> This is an interesting patch series. I've been working in the last 
> weeks in the DRC
> migration, mainly to solve the problem in which a hot CPU unplug will 
> not succeed after
> a migration if the CPU was hotplugged in the source. The problem 
> happened when
> migrating with virsh because Libvirt hotplugs the CPU in both source 
> and target, and
> the DRC state of the hotplugged after the migration is inconsistent. 
> This series solves the
> issue by preventing it from happening in the first place. Of course 
> that migrating DRC states
> has other uses (pending unplug operations during a migration, for 
> example) so both patch
> series can coexist.
>
> One possible issue I see with this series is that it breaks Libvirt 
> migration entirely if
> a CPU/mem hotplug happens in the target. With your series applied the 
> migration
> fails before start with:

Sorry: if a migration happens in the *source*, before the migration.

>
>
> # ./virsh -c 'qemu:///system' migrate --live --domain dhb_ub1704_nfs 
> --desturi qemu+ssh://target_ip/system --timeout 60 --verbose
> error: internal error: unable to execute QEMU command 'device_add': 
> CPU hotplug not supported without OS
>
> Note that I say "possible issue" because, although I believe we do not 
> want to break Libvirt
> if possible, I also believe that we need to think about what makes 
> sense in QEMU first.
>
>
>
> Thanks,
>
>
> Daniel
>
>
> On 05/23/2017 08:18 AM, Laurent Vivier wrote:
>> If the OS is not started, QEMU sends an event to the OS
>> that is lost and cannot be recovered. An unplug is not
>> able to restore QEMU in a coherent state.
>> So, while the OS is not started, disable CPU and memory hotplug.
>> We use option vector 6 to know if the OS is started
>>
>> This series moves error checking for memory hotplug
>> in a pre_plug function, and introduces the option
>> vector 6 management. It also revert previous
>> fix which was not really fixing the hotplug problem
>> when the OS is not running.
>>
>> Laurent Vivier (4):
>>    spapr: add pre_plug function for memory
>>    spapr: add option vector 6
>>    spapr: disable hotplugging without OS
>>    Revert "spapr: fix memory hot-unplugging"
>>
>>   hw/ppc/spapr.c              | 103 
>> ++++++++++++++++++++++++++++++++++++--------
>>   hw/ppc/spapr_drc.c          |  20 ++-------
>>   hw/ppc/spapr_hcall.c        |   5 ++-
>>   hw/ppc/spapr_ovec.c         |   8 ++++
>>   include/hw/ppc/spapr.h      |   2 +
>>   include/hw/ppc/spapr_drc.h  |   1 -
>>   include/hw/ppc/spapr_ovec.h |   7 +++
>>   7 files changed, 109 insertions(+), 37 deletions(-)
>>
>
>