perf kvm: Finding struct machine fails for PERF_RECORD_MMAP

Running 'perf kvm --host --guest --guestmount /tmp/guestmount record -a -g -- sleep 2'

Was resulting in a segfault. For event type PERF_RECORD_MMAP,
event->ip.pid is being used in perf_session__find_machine_for_cpumode,
which is not correct.

The event->ip.pid field happens to be 0 in this case and results in
returning a NULL machine object. Finally, access to self->pid in
machine__mmap_name, results in a segfault later.

For PERF_RECORD_MMAP type, pass event->mmap.pid.
Signed-off-by: Nikunj A. Dadhania <nikunj@linux.vnet.ibm.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Tested-by: David Ahern <dsahern@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Cc: Nikunj A. Dadhania <nikunj@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20120409081835.10576.22018.stgit@abhimanyu.in.ibm.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/session.c

@@ -826,8 +826,16 @@ static struct machine *
 {
 	const u8 cpumode = event->header.misc & PERF_RECORD_MISC_CPUMODE_MASK;
 
-	if (cpumode == PERF_RECORD_MISC_GUEST_KERNEL && perf_guest)
-		return perf_session__find_machine(session, event->ip.pid);
+	if (cpumode == PERF_RECORD_MISC_GUEST_KERNEL && perf_guest) {
+		u32 pid;
+
+		if (event->header.type == PERF_RECORD_MMAP)
+			pid = event->mmap.pid;
+		else
+			pid = event->ip.pid;
+
+		return perf_session__find_machine(session, pid);
+	}
 
 	return perf_session__find_host_machine(session);
 }