6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Adrian Hunter <adrian.hunter@xxxxxxxxx>
commit d92792a4b26e50b96ab734cbe203d8a4c932a7a9 upstream.
pt_event_snapshot_aux() uses pt->handle_nmi to determine if tracing
needs to be stopped, however tracing can still be going because
pt->handle_nmi is set to zero before tracing is stopped in pt_event_stop,
whereas pt_event_snapshot_aux() requires that tracing must be stopped in
order to copy a sample of trace from the buffer.
Instead call pt_config_stop() always, which anyway checks config for
RTIT_CTL_TRACEEN and does nothing if it is already clear.
Note pt_event_snapshot_aux() can continue to use pt->handle_nmi to
determine if the trace needs to be restarted afterwards.
Fixes: 25e8920b301c ("perf/x86/intel/pt: Add sampling support")
Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20240715160712.127117-2-adrian.hunter@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/events/intel/pt.c | 15 +++++++--------
1 file changed, 7 insertions(+), 8 deletions(-)
--- a/arch/x86/events/intel/pt.c
+++ b/arch/x86/events/intel/pt.c
@@ -1602,6 +1602,7 @@ static void pt_event_stop(struct perf_ev
* see comment in intel_pt_interrupt().
*/
WRITE_ONCE(pt->handle_nmi, 0);
+ barrier();
pt_config_stop(event);
@@ -1653,11 +1654,10 @@ static long pt_event_snapshot_aux(struct
return 0;
/*
- * Here, handle_nmi tells us if the tracing is on
+ * There is no PT interrupt in this mode, so stop the trace and it will
+ * remain stopped while the buffer is copied.
*/
- if (READ_ONCE(pt->handle_nmi))
- pt_config_stop(event);
-
+ pt_config_stop(event);
pt_read_offset(buf);
pt_update_head(pt);
@@ -1669,11 +1669,10 @@ static long pt_event_snapshot_aux(struct
ret = perf_output_copy_aux(&pt->handle, handle, from, to);
/*
- * If the tracing was on when we turned up, restart it.
- * Compiler barrier not needed as we couldn't have been
- * preempted by anything that touches pt->handle_nmi.
+ * Here, handle_nmi tells us if the tracing was on.
+ * If the tracing was on, restart it.
*/
- if (pt->handle_nmi)
+ if (READ_ONCE(pt->handle_nmi))
pt_config_start(event);
return ret;
