From aa8e21c053d72b6639ea5a7f1d3a1d0209534c94 Mon Sep 17 00:00:00 2001
From: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Date: Wed, 25 Nov 2020 02:26:55 -0500
Subject: [PATCH] powerpc/perf: Exclude kernel samples while counting events in
 user space.

References: bsc#1065729
Patch-mainline: v5.11-rc1
Git-commit: aa8e21c053d72b6639ea5a7f1d3a1d0209534c94

Perf event attritube supports exclude_kernel flag to avoid
sampling/profiling in supervisor state (kernel). Based on this event
attr flag, Monitor Mode Control Register bit is set to freeze on
supervisor state. But sometimes (due to hardware limitation), Sampled
Instruction Address Register (SIAR) locks on to kernel address even
when freeze on supervisor is set. Patch here adds a check to drop
those samples.

Cc: stable@vger.kernel.org
Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1606289215-1433-1-git-send-email-atrajeev@linux.vnet.ibm.com
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
 arch/powerpc/perf/core-book3s.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index c0e5ea3d6b25..b027884173ee 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -2158,6 +2158,16 @@ static void record_and_restart(struct perf_event *event, unsigned long val,
 	local64_set(&event->hw.period_left, left);
 	perf_event_update_userpage(event);
 
+	/*
+	 * Due to hardware limitation, sometimes SIAR could sample a kernel
+	 * address even when freeze on supervisor state (kernel) is set in
+	 * MMCR2. Check attr.exclude_kernel and address to drop the sample in
+	 * these cases.
+	 */
+	if (event->attr.exclude_kernel && record)
+		if (is_kernel_addr(mfspr(SPRN_SIAR)))
+			record = 0;
+
 	/*
 	 * Finally record data if requested.
 	 */
-- 
2.26.2