[PATCH 4/4] powerpc/perf: Exclude kernel samples while counting events in user space.

[Athira Rajeev]

By setting exclude_kernel for user space profiling, we set the
freeze bits in Monitor Mode Control Register. Due to hardware
limitation, sometimes, Sampled Instruction Address register (SIAR)
captures kernel address even when counter freeze bits are set in
Monitor Mode Control Register (MMCR2). Patch adds a check to drop
these samples at such conditions.

Signed-off-by: Athira Rajeev <atrajeev at linux.vnet.ibm.com>
---
 arch/powerpc/perf/core-book3s.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index c018004..10a2d1f 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -2143,6 +2143,18 @@ static void record_and_restart(struct perf_event *event, unsigned long val,
 	perf_event_update_userpage(event);
 
 	/*
+	 * Setting exclude_kernel will only freeze the
+	 * Performance Monitor counters and we may have
+	 * kernel address captured in SIAR. Hence drop
+	 * the kernel sample captured during user space
+	 * profiling. Setting `record` to zero will also
+	 * make sure event throlling is handled.
+	 */
+	if (event->attr.exclude_kernel && record)
+		if (is_kernel_addr(mfspr(SPRN_SIAR)))
+			record = 0;
+
+	/*
 	 * Finally record data if requested.
 	 */
 	if (record) {
-- 
1.8.3.1