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Re: Introducing non-RAM managed page ("device page")
On Wed, 16 Sep 2009, Masao Uebayashi wrote:
> > The VM subsystem does not fiddle with the MMU. pmap does. The VM
> > subsystem just keeps track of how pages are used. It's been this way
> > since at least BSD 4.4.
> And we don't have API to tell pmap(9) extra information how to map the region.
> Device pages are always mapped as non-cached now. There're cases you want
> to map devices with cache enabled, or other configurations like
> I think such configuration informations should be kept in UVM (== struct
> vm_page *), other than calling cdev_mmap() each time when it's mapped. By
> making device pages as struct vm_page * and teach the generic uvm_fault()
> how to handle them, udv_fault() can go away in the long-run.
Well, you need to be a bit careful about that. On some machines if you
try to enable caching on anything other than RAM the machine will trap.
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