[PATCH] x86_64: fix last_tsc calculation of PM timer

From: "Jan Beulich" <jbeulich@novell.com>

The PM timer code updates vxtime.last_tsc, but this update was done
incorrectly in two ways:
- offset_delay being in microseconds requires multiplying with cpu_mhz
  rather than cpu_khz
- the multiplication of offset_delay and cpu_khz (both being 32-bit
  values) on most current CPUs would overflow (observed value of the
  delay was approximately 4000us, yielding an overflow for frequencies
  starting a little above 1GHz)
Signed-off-by: NJan Beulich <jbeulich@novell.com>
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

arch/x86_64/kernel/pmtimer.c

@@ -68,7 +68,7 @@ int pmtimer_mark_offset(void)
 	offset_delay = delta % (USEC_PER_SEC / HZ);
 
 	rdtscll(tsc);
-	vxtime.last_tsc = tsc - offset_delay * cpu_khz;
+	vxtime.last_tsc = tsc - offset_delay * (u64)cpu_khz / 1000;
 
 	/* don't calculate delay for first run,
 	   or if we've got less then a tick */