RE: [Xen-devel] Error restoring DomU when using GPLPV

["James Harper" <james.harper@xxxxxxxxxxxxxxxx>]

> 
> Could the grant-table/shinfo Xenheap pages be confusing matters I
wonder.
> The save process may save those pages out - since dom0 can map them it
will
> also save them - and then they get mistakenly restored as domheap
pages at
> the far end. All would work out okay in the end when you remap those
special
> pages during GPLPV restore as the domheap pages would get implciitly
freed.
> But maybe there is not allocation headroom for the guest in the
meantime so
> the restore fails.
> 
> Just a theory. Maybe you could try unmapping grant/shinfo pages in the
> suspend callback? This may not help for live migration though, where
pages
> get transmitted before the callback. It may be necessary to allow dom0
to
> specify 'map me a page but not if it's special' and plumb that up to
> xc_domain_save. It'd be good to have the theory proved first.
> 

I took the easier path and told my grant code to map 2 less pages, and
sure enough it tries to allocate 31 pages (which succeeds) but then
tries to allocate 7 (which fails). So the 31 (was 33) must contain the
grant table pages etc. I'll attempt to add the unmap code you requested
and see if it makes a difference...

So why doesn't PV have this problem? Does it not send the pages first?
And do you think that a Linux HVM domain with PV drivers would suffer
the same fate?

Thanks

James

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