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Subject: Re: [PATCH v16 QEMU 08/16] vfio: Register SaveVMHandlers for VFIO
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To: "Dr. David Alan Gilbert" <dgilbert@redhat.com>, Cornelia Huck
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On 5/6/2020 10:23 PM, Dr. David Alan Gilbert wrote:
> * Cornelia Huck (cohuck@redhat.com) wrote:
>> On Wed, 6 May 2020 02:38:46 -0400
>> Yan Zhao <yan.y.zhao@intel.com> wrote:
>>
>>> On Tue, May 05, 2020 at 12:37:26PM +0800, Alex Williamson wrote:
>>>> It's been a long time, but that doesn't seem like what I was asking.
>>>> The sysfs version checking is used to select a target that is likely to
>>>> succeed, but the migration stream is still generated by a user and the
>>>> vendor driver is still ultimately responsible for validating that
>>>> stream.  I would hope that a vendor migration stream therefore starts
>>>> with information similar to that found in the sysfs interface, allowing
>>>> the receiving vendor driver to validate the source device and vendor
>>>> software version, such that we can fail an incoming migration that the
>>>> vendor driver deems incompatible.  Ideally the vendor driver might also
>>>> include consistency and sequence checking throughout the stream to
>>>> prevent a malicious user from exploiting the internal operation of the
>>>> vendor driver.  Thanks,
>>
>> Some kind of somewhat standardized marker for driver/version seems like
>> a good idea. Further checking is also a good idea, but I think the
>> details of that need to be left to the individual drivers.
> 
> Standardised markers like that would be useful; although the rules of
> how to compare them might be a bit vendor specific; but still - it would
> be good for us to be able to dump something out when it all goes wrong.
> 

Such checking should already there in vendor driver. Vendor driver might 
also support across version migration. I think checking in QEMU again 
would be redundant. Let vendor driver handle version checks.

Thanks,
Kirti

>>>>    
>>> maybe we can add a rw field migration_version in
>>> struct vfio_device_migration_info besides sysfs interface ?
>>>
>>> when reading it in src, it gets the same string as that from sysfs;
>>> when writing it in target, it returns success or not to check
>>> compatibility and fails the migration early in setup phase.
>>
>> Getting both populated from the same source seems like a good idea.
>>
>> Not sure if a string is the best value to put into a migration stream;
>> maybe the sysfs interface can derive a human-readable string from a
>> more compact value to be put into the migration region (and ultimately
>> the stream)? Might be overengineering, just thinking out aloud here.
> 
> A string might be OK fi you specify a little about it.
> 
> Dave
> 
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>