Re: Buggy interaction of live migration and p2m updates

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 21/11/14 10:43, Jan Beulich wrote:
>>>> On 20.11.14 at 19:28, <andrew.cooper3@citrix.com> wrote:
>> Should the guest change the p2m structure during live migration, the
>> toolstack ends up with a stale p2m with a non-p2m frame in the middle,
>> resulting in bogus cross-referencing.  Should the guest change an entry
>> in the p2m, the p2m frame itself will be resent as it would be marked as
>> dirty in the logdirty bitmap, but the target pfn will remain unsent and
>> probably stale on the receiving side.
> MMU_MACHPHYS_UPDATE processing marks the page being changed
> as dirty. Perhaps guest_physmap_{add,remove}_page() (or certain
> callers thereof) should do so too?
>
> Jan
>

This is certainly needed to fix HVM ballooning and live migration
issues, although now you point it out, it applies just as much to PV
guests as HVM guests.

I believe this might allow the toolstack to avoid keeping a second copy
of the p2m.

~Andrew