Re: [Xen-devel] Guest OS without paging

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> 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.

Out of interest, what exactly does it do with segmentation?  Most CPUs don't 
have segmentation hardware at all...  I can imagine ways they might have 
overlaid it on the flat memory model without affective other ports though...  
Task isolation?  Kernel / user protection?

Cheers,
Mark

> > 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
>
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