Re: [Xen-devel] Migration memory corruption - PV backends need to quiesce

[Tim Deegan <tim@xxxxxxx>]

At 18:28 +0100 on 27 Jun (1403890088), David Vrabel wrote:
> On 27/06/14 17:51, Andrew Cooper wrote:
> > 
> > Overall, it would appear that there needs to be a hook for all PV
> > drivers to force quiescence.  In particular, a backend must guarantee to
> > unmap all active grant maps (so the frames get properly reflected in the
> > dirty bitmap), and never process subsequent requests (so no new frames
> > appear dirty in the bitmap after the guest has been paused).
> 
> I think this would be much too expensive for snapshots and things like
> remus.  Waiting for all outstanding I/O could take seconds.

The other option we talked about yesterday was a flag to the log-dirty
operation that reports all grant-mapped frames as dirty.  Then the
tools would add such frames to the final pass.  That could take a long
time too, of course.

I'm not sure how you would synchronize the final pass with backends
that were doing grant copy operations -- you could exclude copies for
the duration, but I'm not sure what that would look like for the
backend.

Tim.

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