[PATCH] perf/x86/intel/pt: Fix crash with stop filters in single-range mode

[Tristan Hume <tristan@thume.ca>]

Add a check for !buf->single before calling pt_buffer_region_size in a
place where a missing check can cause a kernel crash.

Fixes a bug introduced by 670638477aede0d7a355ced04b569214aa3feacd,
which added a support for PT single-range output mode. Since that commit
if a PT stop filter range is hit while tracing, the kernel will crash
because of a null pointer dereference in pt_handle_status due to calling
pt_buffer_region_size without a ToPA configured.

The commit which introduced single-range mode guarded almost all uses of
the ToPA buffer variables with checks of the buf->single variable, but
missed the case where tracing was stopped by the PT hardware, which
happens when execution hits a configured stop filter.

Tested that hitting a stop filter while PT recording successfully
records a trace with this patch but crashes without this patch.

Signed-off-by: Tristan Hume <tristan@thume.ca>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/events/intel/pt.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
index 7f406c14715f..2d33bba9a144 100644
--- a/arch/x86/events/intel/pt.c
+++ b/arch/x86/events/intel/pt.c
@@ -897,8 +897,9 @@ static void pt_handle_status(struct pt *pt)
 		 * means we are already losing data; need to let the decoder
 		 * know.
 		 */
-		if (!intel_pt_validate_hw_cap(PT_CAP_topa_multiple_entries) ||
-		    buf->output_off == pt_buffer_region_size(buf)) {
+		if (!buf->single &&
+		    (!intel_pt_validate_hw_cap(PT_CAP_topa_multiple_entries) ||
+		     buf->output_off == pt_buffer_region_size(buf))) {
 			perf_aux_output_flag(&pt->handle,
 			                     PERF_AUX_FLAG_TRUNCATED);
 			advance++;
-- 
2.21.1 (Apple Git-122.3)