Re: l4ka Digest, Vol 30, Issue 12

Espen,

On Friday 02 June 2006 15:58, Espen Skoglund wrote:
> > Sure, Pistachio sigma0 can map pages it can't access, it just means
> > that you complicate the issue of setting up and managing page
> > attributes (uncached, write-through etc) since sigma0 can't modify
> > the attributes of those pages.
>
> I wouldn't say that it complicates the issue more than it already is.
> Mind you, MemoryControl() is really badly defined right now.  The way
> you describe things with page attributes assumes one particular
> definition of how these things are supposed to work.  If you remember
> the proposed MapControl() syscall (internal mail, not on l4ka@ mailing
> list), you might also remember a lengthy mail where I among other
> things described how managing page attributes from sigma0 is a
> terribly, terribly bad idea.

would appreciate some more comments on this from you. Naively spoken,
different physical frames can have different page attributes. It is not
necessary (as far as I can see) that the same physical frame is mapped
cacheable to one address space and non-cacheable to another address space.
The same applies for write through / write back.

Since Sigma0 is the ``creator'' of physical pages it should be able to
manage page attributes and could do this using MemoryControl. Other
servers asking Sigma0 to map a specific page specify their wishes for
the attribute of the corresponding physical frame. Sigma0 is also able
to setup MTRRs if requested since it is a privileged task.

Kind regards,

Frank
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