MFC r330511:

MFC r330511:
  We shouldn't need to execute code in the recursive page table mappings;
  therefore, it should be safe to set the NX bit on the PML4E for the
  recursive page table mappings.  According to the Intel docs, the effect
  of the NX bit should propogate to any page reached through a PML4E which
  has the NX bit set.

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