Re: [Xen-devel] [PATCH] fix memory exchange hypercall.

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

On Thu, Mar 15, 2007 at 10:59:33AM +0000, Keir Fraser wrote:
> Do the p2m semantics of the two architectures really need to differ? Can't
> ia64 match x86 semantics (or vice versa)? Otherwise you're going to be
> continually getting broken and having to implement skanky workarounds.

I fully agree with you.
I've tried, but I haven't found any good way yet. :-(.


The big differrence is that the x86 p2m table (i.e. hvm domain)
doesn't support foreign domain page mapping and grant table page mapping.
On the other hand, the ia64 p2m supports them.
(NOTE:The ia64 p2m is used for both para/full virtualized domain.
Even for dom0. So they must be supported.)

For that purpose, the ia64 p2m table semantic is something
similar to (the x86 p2m table) + (the x86 page table reference counting).
(NOTE:those page mapping are based on virtual address
with x86 paravirtualized domain. On the other hand they are based
on pseudo physical address with auto translated physmap mode
i.e. hvm domain or ia64 domain.
This is the root cause of the difference.)

If the x86 p2m table supported those page mapping, 
the similar semantics would be necessary, I suppose.
But it won't happen in the near future.
-- 
yamahata

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