Re: treatment grant frames during save/restore

[Keir Fraser <keir.fraser@eu.citrix.com>]

On 27/05/2010 16:27, "Jan Beulich" <JBeulich@novell.com> wrote:

>> From what I can tell, grant frames get no special treatment by the tools
> during save, and hence get treated as normal memory during restore.
> If that's correct, it would seem that there's an accounting issue, since
> during restore a normal RAM page will be allocated by the tools for each
> grant frame, hence a domain that prior to save was below its limit
> could now end up crossing that limit, and thus unexpectedly fail to
> restore. If that's not a possibility, what am I missing?

Yes, it's an issue. Fixing is tricky since in some cases dom0 *wants* to be
able to map domU special Xen-heap pages. So we need to be able to specify
some kind of flag to say 'really map this domain's domain-heap RAM pages
only on this request' and preferably tunnel that flag through existing dom0
kernels so that it makes it unscathed down to the Xen hypercall. That's a
bit tricky I think, unless we do nasty things like steal bits from the
existing domid or pte.val fields to mmu_update(). Else we need dom0 kernel
mods too, which is a pain in the bum, but I suppose we could do that with
fallback to what we do currently.

 -- Keir

> Thanks, Jan
> 
> 
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