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Re: [Xen-devel] treatment grant frames during save/restore

>>> On 28.05.10 at 10:22, Keir Fraser <keir.fraser@xxxxxxxxxxxxx> wrote:
> On 28/05/2010 09:01, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
>> Wouldn't is suffice to adjust XEN_DOMCTL_getpageframeinfo{2,3} to
>> report these pages as special (not sure whether a new type would
>> be needed, or whether simply returning XEN_DOMCTL_PFINFO_XTAB
>> would be acceptable), thus allowing the tools to skip them as
>> necessary? This of course implies that the tools would need to issue
>> the call for HVM guests (currently I think they do so only for PV ones),
>> that the actual page contents is irrelevant post-restore, and that
>> there being a hole in the physical address space post-restore isn't
>> a problem for the pv drivers.
> Yep that would probably work. And also potentially gets rid of one lot of
> "if-hvm-else-pv" branched code in xc_domain_save.c. I'd take a patch to do
> that if you want to pick this item up.

I'm afraid it won't: The live_p2m table gets created for pv guests only,
but is needed as a prerequisite to calling XEN_DOMCTL_getpageframeinfo*
(which wants MFNs as input). Hence while the hypervisor side patch is
trivial, it doesn't get us any closer to a solution to the problem at hand.

Unless we (re-)define the meaning of the input array to this domctl to
specify gmfn-s rather than mfn-s (at least for the hvm case; for
auto-translate pv guests, quite obviously the save code wouldn't
work anyway, but for those passing in gmfn-s would seem the
natural thing here).

Or unless we want to add code to libxc to create a live_p2m for all
guests (which I wouldn't want to take on).


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