the kernel's direct map instead of the pmap's recursive mapping to access
the lowest level in the page table. The direct map is preferable for two
reasons: (1) The TLB is more likely to hold the required direct mapping
because pmap_enter() has already used the direct map to access a nearby
PTE and (2) loading a direct mapping into the TLB involves walking only 2
or 3 levels of the page table instead of 4.
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