Re: [RFC PATCH V2 0/3] IXGBE/VFIO: Add live migration support for SRIOV NIC

["Lan, Tianyu" <tianyu.lan-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>]

On 12/9/2015 6:37 PM, Michael S. Tsirkin wrote:
> On Sat, Dec 05, 2015 at 12:32:00AM +0800, Lan, Tianyu wrote:
>> Hi Michael & Alexander:
>> Thanks a lot for your comments and suggestions.
>
> It's nice that it's appreciated, but you then go on and ignore
> all that I have written here:
> https://www.mail-archive.com/kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org/msg123826.html
>

No, I will reply it separately and according your suggestion to snip it 
into 3 thread.

>> We still need to support Windows guest for migration and this is why our
>> patches keep all changes in the driver since it's impossible to change
>> Windows kernel.
>
> This is not a reasonable argument.  It makes no sense to duplicate code
> on Linux because you must duplicate code on Windows.  Let's assume you
> must do it in the driver on windows because windows has closed source
> drivers.  What does it matter? Linux can still do it as part of DMA API
> and have it apply to all drivers.
>

Sure. Duplicated code should be encapsulated and make it able to reuse
by other drivers. Just like you said the dummy write part.

I meant the framework should not require to change Windows kernel code
(such as PM core or PCI bus driver)and this will block implementation on
the Windows.

I think it's not problem to duplicate code in the Windows drivers.

>> Following is my idea to do DMA tracking.
>>
>> Inject event to VF driver after memory iterate stage
>> and before stop VCPU and then VF driver marks dirty all
>> using DMA memory. The new allocated pages also need to
>> be marked dirty before stopping VCPU. All dirty memory
>> in this time slot will be migrated until stop-and-copy
>> stage. We also need to make sure to disable VF via clearing the
>> bus master enable bit for VF before migrating these memory.
>>
>> The dma page allocated by VF driver also needs to reserve space
>> to do dummy write.
>
> I suggested ways to do it all in the hypervisor without driver hacks, or
> hide it within DMA API without need to reserve extra space. Both
> approaches seem much cleaner.
>

This sounds reasonable. We may discuss it detail in the separate thread.