Mapping Physical Memory without a Device?

[cd_freebsd]

jmallett at freebsd.org writes

>> You may also want to consider pmap_map.  It depends on what your >>requirements are?

while Bruce M Simpson [bms at spc.org] writes

>>It's quite evil and not machine independent..avoid.

-Who is right? (I like Juli's answer and she has FreeBSD.org in her name :) ) 
-Why is pmap_mapdev bad? 
-What makes it machine dependent?
-What is the difference between pmap_devmap and pmap_map?

My requirements would be to map some or all of the following memory areas that are not associated with any device I own:
1) BIOS & UMB ram (0xC0000-0xFFFFF)
2) VGA Video buffer (0xA0000-0xBFFFF)
3) Video Frame buffer (0x????0000-0x????0000)