Re: [Qemu-devel] [PATCH v2 0/8] nvdimm: hotplug support

[Xiao Guangrong <guangrong.xiao@linux.intel.com>]

On 10/11/2016 08:32 PM, Igor Mammedov wrote:

>>
>> Of course, @fit and @current_number should be persistent during live migration.
> you can drop RCU and @current_number,
> and @fit could be exactly recreated on target side from
>  -device nvdim ...
> set of options, which must include all currently present
> (including hotplugged) devices from source side.
>
> It's sufficient to invalidate and restart DMA transfer in flight.
>
> i.e.
> pc_dimm_memory_plug ()
>   -> regenerate_fit()
>       -> set local flag @fit-dirty
>
>   -> start QEMU.fit_read()
>       -> if offset == 0 ? clear @fit-dirty
>       make sure fit_read() won't conflict with regenerate_fit()
>         either plain mutex or RCU would do the job
>
>   ...
>   OSPM.rfit()
>      ...
>      if (@fit-dirty)
>          abort/restart DMA from start
>
> In migration case, the target would have @fit-dirty set thanks to
> pc_dimm_memory_plug () -> regenerate_fit() and any DMA in flight
> would be restarted.
> That's a little bit inefficient as source_fit exactly matches
> target_fit and DMA could continue, but it would save us from
> having fit specific migration state to transfer and maintain.
>

Nice, that works. :-)

Thanks!