The reason for cpu_reload_memory_map()'s RCU operations is not
so much because the guest could make the critical section very
long, but that it could have a critical section within which
it made an arbitrary number of changes to the memory map and
thus accumulate an unbounded amount of memory data structures
awaiting reclamation. Clarify the comment to make this clearer.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <1443709790-25180-3-git-send-email-peter.maydell@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>