Re: [Xen-devel] Guest OS without paging

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> > IMO, if you really need a Minix-specific builder, you might as well have
> > it set up the page tables for you too.  This will probably make life
> > simpler for development, in any case.
>
> ok, so in this scenario, id have to create a page table with a 1-1 mapping
> of page frames to page table entries in the builder?

That would give you a flat linear memory space, enabling you to largely ignore 
the fact that paging is active...

> would I still need to 
> put code in the minix kernel itself to handle page faults, or is it
> possible to have all pages loaded from start of day, but calling something
> in the builder?

I guess I'm not clear what memory model you need for Minix, can you clarify?  
What version of Minix is this?  Does it really not do any virtual memory of 
its own?  Does it do any tricks at all (demand paging?  page sharing?), or 
does it run unpaged or something else?

Domains get a hard allocation of real memory, so when the pages get populated 
is entirely up to the guest; Xen won't interfere.

If you essentially want to pretend you've got a flat, unpaged address space 
then you should be able to just be able to build a set of page tables (for 
instance in your custom builder) and then pretend they're not there.  Just 
remember that you can't use the very top part of the address space because 
Xen will be mapped there.

If Minix actually expects to use page tables for something then you'll have to 
do more work in the memory management department to make it work under Xen...

HTH,
Mark

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