Re: Kernel support for peer-to-peer protection models...
From: Pavel Machek (pavel_at_ucw.cz)
Date: 03/28/04
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Date: Sun, 28 Mar 2004 20:54:10 +0200 To: Ivan Godard <igodard@pacbell.net>
Hi!
> > I meant "User Mode Linux" == linux running under linux. Someone
> > probably has an URL.
>
> Sorry - I plead ignorance :-) As the protection is recursive and
> transitive, I suppose that you could do this. When the UMK (user mode
> kernel) went to change the "real" machine it would get a protection fault
> that would be handled by the KMK, emulating the effect. Getting it right and
> also performant would be tricky though - is UML a necessary feature?
No. Its just "nice to have", and it does not support too many
architectures.
> > Strange system.... If an application does not grant kernel access to
> > its space, how is kernel supposed to do its job? For example, that
> > "paranoid DLL" becomes unswappable, then?
>
> Pretection is in the *virtual* space, not physical. The physical-page
> manager (who has the TLB and underlying mapping tables in its space) can see
> and deal with any physical address, which in turn has the usual aliasing
> relationship with virtual addresses. Of course, physical is just one of the
> virtual spaces (and is distinguished solely by the one-to-one
> virtual-physical mapping). So the protection can be penetrated by anyone who
> can see the underlying physical page - but that's always true.
Aha, so some part of kernel exist that has "absolute right". Ok, now I
can imagine that it can work.
> > If most changes are in arch/, it should be acceptable...
>
> I fear that it might be more extensive than that :-)
Well, make patch and lets see... That means that 2.8 needs to be your
target. If impact outside of arch is not "total rewrite", you might
have a chance. If it is "total rewrite".... well you just need to be
very clever.
Pavel
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