Begin weaning user-only away from PageDesc.
Since, for user-only, all TB (and page) manipulation is done with
a single mutex, and there is no virtual/physical discontinuity to
split a TB across discontinuous pages, place all of the TBs into
a single IntervalTree. This makes it trivial to find all of the
TBs intersecting a range.
Retain the existing PageDesc + linked list implementation for
system mode. Move the portion of the implementation that overlaps
the new user-only code behind the common ifdef.
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
a97d5d2c8b