perf: 'perf kvm' tool for monitoring guest performance from host

Here is the patch of userspace perf tool.

Signed-off-by: Zhang Yanmin <yanmin_zhang@linux.intel.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/tools/perf/perf.h b/tools/perf/perf.h
index ec21274..02821fe 100644
--- a/tools/perf/perf.h
+++ b/tools/perf/perf.h
@@ -131,4 +131,6 @@
 	u64 ips[0];
 };
 
+extern int perf_host, perf_guest;
+
 #endif