Jason Thorpe said:
> On Mon, 1 Feb 1999 11:52:59 -0500 
>  Chuck Cranor <chuck@research.att.com> wrote:
> 
>  > regarding the usage of pmap_kenter and its interaction with
>  > mod/ref bits and VAC aliases: you are only supposed to use
>  > pmap_kenter() for mapping where those issues don't matter
>  > (e.g. private kernel mappings).   John Dyson's message clearly
>  > explained it the way i was thinking about it so i won't bother 
>  > to repeat it again.
> 
> Hm, okay.
> 
> But, what happens on VAC systems if you e.g. mmap /dev/mem, and happen
> to mmap one of those pages?
> 
> Regarding the use of pmap_kenter() and uvm_loan(), perhaps I misunderstood
> something you said when we discussed that in private e-mail all those
> months ago.  "Dave, my mind is going..."
> 
No problem -- if you need to support a machine with aliasing problems, then
it means that supporting the aliasing might require addition of some
cap-abilities to pmap_kenter/pmap_kremove...

Mapping /dev/(k)mem on machines without aliasing problems isn't a real
problem, because the user mappings will have the pv entries.  A modification
required to pmap_kremove (even in the FreeBSD codebase), would be to chase
down the pv entries.  That overhead would be needed only if there were any pv
entries, which would be an exceptional circumstance.

-- 
John                  | Never try to teach a pig to sing,
dyson@iquest.net      | it makes one look stupid
jdyson@nc.com         | and it irritates the pig.