[PATCH v3 2/2] selftests/powerpc: Test for spurious kernel memory faults on radix

[Jordan Niethe]

Previously when mapping kernel memory on radix, no ptesync was included
which would periodically lead to unhandled spurious faults. Mapping
kernel memory is used when code patching with Strict RWX enabled.  As
suggested by Chris Riedl, turning ftrace on and off does a large amount
of code patching so is a convenient way to see this kind of fault.

Add a selftest to try and trigger this kind of a spurious fault. It
tests for 30 seconds which is usually long enough for the issue to show
up.

Signed-off-by: Jordan Niethe <jniethe5 at gmail.com>
---
v3: New to series
---
 tools/testing/selftests/powerpc/mm/Makefile   |  1 +
 .../selftests/powerpc/mm/spurious_fault.sh    | 49 +++++++++++++++++++
 2 files changed, 50 insertions(+)
 create mode 100755 tools/testing/selftests/powerpc/mm/spurious_fault.sh

diff --git a/tools/testing/selftests/powerpc/mm/Makefile b/tools/testing/selftests/powerpc/mm/Makefile
index defe488d6bf1..56c2896bed53 100644
--- a/tools/testing/selftests/powerpc/mm/Makefile
+++ b/tools/testing/selftests/powerpc/mm/Makefile
@@ -5,6 +5,7 @@ noarg:
 TEST_GEN_PROGS := hugetlb_vs_thp_test subpage_prot prot_sao segv_errors wild_bctr \
 		  large_vm_fork_separation bad_accesses pkey_exec_prot \
 		  pkey_siginfo stack_expansion_signal stack_expansion_ldst
+TEST_PROGS := spurious_fault.sh
 
 TEST_GEN_PROGS_EXTENDED := tlbie_test
 TEST_GEN_FILES := tempfile
diff --git a/tools/testing/selftests/powerpc/mm/spurious_fault.sh b/tools/testing/selftests/powerpc/mm/spurious_fault.sh
new file mode 100755
index 000000000000..e454509659f6
--- /dev/null
+++ b/tools/testing/selftests/powerpc/mm/spurious_fault.sh
@@ -0,0 +1,49 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+TIMEOUT=30
+
+DEBUFS_DIR=`cat /proc/mounts | grep debugfs | awk '{print $2}'`
+if [ ! -e "$DEBUFS_DIR" ]
+then
+	echo "debugfs not found, skipping" 1>&2
+	exit 4
+fi
+
+if [ ! -e "$DEBUFS_DIR/tracing/current_tracer" ]
+then
+	echo "Tracing files not found, skipping" 1>&2
+	exit 4
+fi
+
+
+echo "Testing for spurious faults when mapping kernel memory..."
+
+if grep -q "FUNCTION TRACING IS CORRUPTED" "$DEBUFS_DIR/tracing/trace"
+then
+	echo "FAILED: Ftrace already dead. Probably due to a spurious fault" 1>&2
+	exit 1
+fi
+
+dmesg -C
+START_TIME=`date +%s`
+END_TIME=`expr $START_TIME + $TIMEOUT`
+while [ `date +%s` -lt $END_TIME ]
+do
+	echo function > $DEBUFS_DIR/tracing/current_tracer
+	echo nop > $DEBUFS_DIR/tracing/current_tracer
+	if dmesg | grep -q 'ftrace bug'
+	then
+		break
+	fi
+done
+
+echo nop > $DEBUFS_DIR/tracing/current_tracer
+if dmesg | grep -q 'ftrace bug'
+then
+	echo "FAILED: Mapping kernel memory causes spurious faults" 1>&2
+	exit 1
+else
+	echo "OK: Mapping kernel memory does not cause spurious faults"
+	exit 0
+fi
-- 
2.25.1