perf/x86/msr: Fix SMI overflow

We compute 'delta' and properly sign extend it and then ignore it and
recompute the raw value, loosing the sign extention.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: kan.liang@intel.com
Cc: linux-kernel@vger.kernel.org
Cc: luto@kernel.org
Cc: ray.huang@amd.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/events/msr.c

@@ -166,7 +166,7 @@ static void msr_event_update(struct perf_event *event)
 	if (unlikely(event->hw.event_base == MSR_SMI_COUNT))
 		delta = sign_extend64(delta, 31);
 
-	local64_add(now - prev, &event->count);
+	local64_add(delta, &event->count);
 }
 
 static void msr_event_start(struct perf_event *event, int flags)