Dave,
A most hearty thanks for the help. It appears that the solution was to
change:
MmProbeAndLockPages(…);
MmGetSystemAddressForMdl(…);
to simply
MmProbeAndLockPages(…);
Now I’m not burning PTEs when I don’t need to and things are happy in
Mudville, once more. 
Thanks again, and a happy holidays to you and yours.
Gary
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