Yes, Ericsson, Siemens and possibly many other telco manufacturers use the same solution for
decades. So MS's patent is likely to be invalid.
Patching is a very good thing, as long as you apply the right patches. Just remember the
Ericsson scandal: http://www.spectrum.ieee.org/print/5280
So being able to patch a running kernel is a double edged sword. If someone gains root rights
he can apply a nasty patch secretly and leave immediately.
In most HA systems there is an alternative of patching. On resilient systems you have quite
enough hardware, so all you need to do is update the code (even the most frequently used ones)
on a spare computer, move all the data (incl. data from RAM) there and continue the execution
using the new code (or new hardware, if you had HW issues instead of SW ones). That is how
Nokia DX200 switches work. The same restrictions apply for data structure changes as for