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Device page

As I briefly mentioned before, I'll need device page to support XIP.  It's
a struct vm_page *, which is actually a magic value which conveys data from
pgo_get() to pmap_enter().

When a device page is pmap_enter()'ed, pmap checks if it's a device page or
not, if so, stores a PV into a dedicated vm_physseg for devices.  When a
device page is passed to pmap_page_*() (struct vm_page *-oriented functions),
they look for the device vm_physseg, look up a PV header, then look up a PV.

I also want to make these minimal PV handling moved to some MI place - probably
uvm_page.c.  Now we don't define MI PV header yet, I'll allocate struct
vm_page_md *[] for each XIP-capable device.  This will be put in uvm_page.c


Masao Uebayashi / Tombi Inc. / Tel: +81-90-9141-4635

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