perf/x86/intel/pt: Use pointer arithmetics instead in ToPA entry calculation

Currently, pt_buffer_reset_offsets() calculates the current ToPA entry by
casting pointers to addresses and performing ungainly subtractions and
divisions instead of a simpler pointer arithmetic, which would be perfectly
applicable in that case. Fix that.
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
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>
Link: http://lkml.kernel.org/r/20190821124727.73310-4-alexander.shishkin@linux.intel.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/events/intel/pt.c

@@ -1030,8 +1030,7 @@ static void pt_buffer_reset_offsets(struct pt_buffer *buf, unsigned long head)
 	pg = pt_topa_next_entry(buf, pg);
 
 	buf->cur = (struct topa *)((unsigned long)buf->topa_index[pg] & PAGE_MASK);
-	buf->cur_idx = ((unsigned long)buf->topa_index[pg] -
-			(unsigned long)buf->cur) / sizeof(struct topa_entry);
+	buf->cur_idx = buf->topa_index[pg] - TOPA_ENTRY(buf->cur, 0);
 	buf->output_off = head & (pt_buffer_region_size(buf) - 1);
 
 	local64_set(&buf->head, head);