to simultaneously change the PAT setting for the same pages within the
direct map region. This may require the demotion of a 2MB page mapping and
the allocation of a page table page. This revision gives the highest
possible priority (VM_ALLOC_INTERRUPT) to this page allocation, so that
pmap_change_attr() is less likely to fail. (In general, kernel page table
page allocations have the highest priority, so this is not creating a new
precedent.)
(Demotion of 1GB page mappings within the direct map already specifies
VM_ALLOC_INTERRUPT to vm_page_alloc(), so only pmap_demote_pde() must be
changed.)
Approved by: re (kib)
c9ef1e0104