Re: treatment grant frames during save/restore

["Jan Beulich" <JBeulich@novell.com>]

>>> On 27.05.10 at 18:02, Keir Fraser <keir.fraser@eu.citrix.com> wrote:
> 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.

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.

Jan