Re: Guest OS without paging

[Ivan Kelly <ivan@ivankelly.net>]

On Mon, Nov 07, 2005 at 05:26:19PM +0000, Mark Williamson wrote:
> 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?
well, minix uses segmentation but doesn't use paging at all, because it's
build to be portable and not all processers have a mmu unit(i think the arm
doesn't and such). Im using minix 3. 
> 
> Domains get a hard allocation of real memory, so when the pages get populated 
> is entirely up to the guest; Xen won't interfere.
What about page faults? Will I have to have to write code to handle these, or
can I assume that since im only ever using memory thats alreayd mapped, page
faults wont occur?
> 
> 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.
Thats exactly what I want. Does the 64M address space need to have entries in
my page table or can i just make my guest's pagetable from 64M-xxM. Also,
is there are any pages allocated in this 64M address space, will they my
allocated from the domains pool of page frames, or from dom0's?
Best regards
Ivan