the pv lists in the vm_page, even unmanaged kernel mappings. This is so
that the virtual cachability of these mappings can be tracked when a page
is mapped to more than one virtual address. All virtually cachable
mappings of a physical page must have the same virtual colour, or illegal
alises can be created in the data cache. This is a bit tricky because we
still have to recognize managed and unmanaged mappings, even though they
are all on the pv lists.
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