perf kvm stat live: Enable events copying

perf kvm stat live: Enable events copying

Process of analyzing events caused by 2 functions: mmap_read() and
finished_round().

During mmap_read(), perf receives events from shared memory, queues
their pointers for further processing in finished_round() and notifies
the kernel that the events have been processed.

By the time when finished_round() is invoked, queued events can be
overwritten by the kernel, so the finished_round() occurs on potentially
corrupted memory.

Since there is no place where the event can be safely consumed, let's
copy events when queueing.

Signed-off-by: Alexander Yarygin <[email protected]>
Cc: Christian Borntraeger <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>