Re: [Xen-devel] pagetable pinning question

[Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>]

> I can't comment on the 1.3 problem but for 1.2 it would seem to me that
> simply increasing the L2's reference count when we map a different L2 table
> as a twisted L2 table would keep things sane even in the circular case, as
> long as we unmap in the opposite order.  Or am I missing
> something?

I believe everyone is in agreement as regards how to add support
in 1.2.

The only problem is in 1.3, where pages can potentially be shared
between multiple domains. If one of the domains is destroyed, we
need to think through how to safely reclaim the memory.

> I think I can guarantee that the unmap order is correct if I clear the
> alternate mapping whenever I switch pagetables (and there's no switches
> between a requested mapping and the corresponding unmap).  The pool cache
> destructor would then also only need to check the current pagetable's
> alternate mapping.

With the proposed mod, this should work fine. (with the 1.3
memory reclamation caveat).

Ian


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