Re: Xen at scale

[Kip Macy <kmacy@fsmware.com>]

>
> Now it would seem easy to just not map the memory which will end up in
> highmem but we need to have all the memory mapped initially so that we can
> build the phys_to_machine_mapping array.  I believe you can't build it only
> from the machine_to_phys_mapping array provided by Xen since you don't know
> which pages belong to the domain...

The {DragonFly/Free}BSD domain builder sets the page tables up a little
differently. It populates the phys_to_machine array before starting
the domain - mapping it at a pre-determined address relative to
KERNBASE. In addition it only maps the ktext and a stack page - the
remainder of the pages are mapped at runtime by the same pmap_init used
on native i386.

> I think I would map the highmem pages starting at VA 0, the alternative
> seems to be to pass an array with the page numbers to the domain.

This is done for all pages with a pre-established P->M mapping. The
domain builder passes in the number of pages used by the domain builder
via a register. This is equivalent to the way native locore.s passes
physfree (the address of the first free physical page) to init386.

> Maybe there's a simpler solution?

I don't think passing an array is more complicated.

		-Kip


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