[PATCH v2 4/4] selftests/ftrace: Add persistent ring buffer testcases

["Masami Hiramatsu (Google)" <mhiramat@kernel.org>]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Add test cases for persistent ring buffer (reserve_mem= combined
with trace_instance=) and backup instance (trace_instance=backup=boot_map).

These test cases verify:
 - persistent-01-reserve-mem: Memory reservation via reserve_mem=
   and trace_instance=boot_map@trace. Verifies trace data retention in
   the boot_map instance across guest crash/reboot via sysrq-trigger.
 - persistent-02-backup-instance: Backup instance creation via
   trace_instance=backup=boot_map. Verifies that previous boot trace
   log is preserved in the backup instance on the subsequent boot.

These test cases specify '# REBOOT: 1' to enable multi-boot guest
crash/reboot testing with doubled QEMU timeout.

Assisted-by: Antigravity:gemini-3.6-flash
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
Changes in v2:
 - Increase reserve_mem alignment to 32M (reserve_mem=12M:32M:trace) to
   ensure stable physical memory placement across KASLR reboots.
---
 .../cmdlines/persistent-01-reserve-mem.cmdline     |    1 +
 .../cmdlines/persistent-02-backup-instance.cmdline |    1 +
 .../boottime/tests/persistent-01-reserve-mem.sh    |   28 ++++++++++++++
 .../tests/persistent-02-backup-instance.sh         |   40 ++++++++++++++++++++
 4 files changed, 70 insertions(+)
 create mode 100644 tools/testing/selftests/ftrace/boottime/cmdlines/persistent-01-reserve-mem.cmdline
 create mode 100644 tools/testing/selftests/ftrace/boottime/cmdlines/persistent-02-backup-instance.cmdline
 create mode 100644 tools/testing/selftests/ftrace/boottime/tests/persistent-01-reserve-mem.sh
 create mode 100644 tools/testing/selftests/ftrace/boottime/tests/persistent-02-backup-instance.sh

diff --git a/tools/testing/selftests/ftrace/boottime/cmdlines/persistent-01-reserve-mem.cmdline b/tools/testing/selftests/ftrace/boottime/cmdlines/persistent-01-reserve-mem.cmdline
new file mode 100644
index 000000000000..c69eeb27deb6
--- /dev/null
+++ b/tools/testing/selftests/ftrace/boottime/cmdlines/persistent-01-reserve-mem.cmdline
@@ -0,0 +1 @@
+reserve_mem=12M:32M:trace trace_instance=boot_map@trace
diff --git a/tools/testing/selftests/ftrace/boottime/cmdlines/persistent-02-backup-instance.cmdline b/tools/testing/selftests/ftrace/boottime/cmdlines/persistent-02-backup-instance.cmdline
new file mode 100644
index 000000000000..43217c986ca1
--- /dev/null
+++ b/tools/testing/selftests/ftrace/boottime/cmdlines/persistent-02-backup-instance.cmdline
@@ -0,0 +1 @@
+reserve_mem=12M:32M:trace trace_instance=boot_map@trace trace_instance=backup=boot_map
diff --git a/tools/testing/selftests/ftrace/boottime/tests/persistent-01-reserve-mem.sh b/tools/testing/selftests/ftrace/boottime/tests/persistent-01-reserve-mem.sh
new file mode 100644
index 000000000000..49abaf518481
--- /dev/null
+++ b/tools/testing/selftests/ftrace/boottime/tests/persistent-01-reserve-mem.sh
@@ -0,0 +1,28 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2026, Google LLC.
+# Check persistent ring buffer across guest crash/reboot
+# REBOOT: 1
+TRACEDIR="/sys/kernel/tracing"
+
+if [ ! -f "$TRACEDIR/instances/boot_map/trace" ]; then
+	echo "FAIL: persistent trace instance boot_map/trace file missing"
+	exit 1
+fi
+
+# Check if Boot 1 marker was already written
+if grep -q "BOOT1_MARKER" "$TRACEDIR/instances/boot_map/trace" 2>/dev/null; then
+	# Second boot: verify persistent ring buffer content from first boot
+	echo "PASS: persistent-01-reserve-mem"
+	exit 0
+fi
+
+# First boot: write marker to persistent buffer and trigger kernel crash/reboot
+echo "BOOT1_MARKER" > "$TRACEDIR/instances/boot_map/trace_marker"
+sync
+
+# Trigger reboot to restart into second boot
+echo b > /proc/sysrq-trigger 2>/dev/null || echo c > /proc/sysrq-trigger 2>/dev/null || true
+sleep 5
+echo "FAIL: reboot trigger failed on first boot"
+exit 1
diff --git a/tools/testing/selftests/ftrace/boottime/tests/persistent-02-backup-instance.sh b/tools/testing/selftests/ftrace/boottime/tests/persistent-02-backup-instance.sh
new file mode 100644
index 000000000000..0b2a2f03ce4f
--- /dev/null
+++ b/tools/testing/selftests/ftrace/boottime/tests/persistent-02-backup-instance.sh
@@ -0,0 +1,40 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2026, Google LLC.
+# Check persistent backup instance across guest crash/reboot
+# REBOOT: 1
+TRACEDIR="/sys/kernel/tracing"
+
+# Ensure both boot_map/trace and backup/trace files exist
+if [ ! -f "$TRACEDIR/instances/boot_map/trace" ]; then
+	echo "FAIL: boot_map/trace file missing"
+	exit 1
+fi
+
+if [ ! -f "$TRACEDIR/instances/backup/trace" ]; then
+	echo "FAIL: backup/trace file missing"
+	exit 1
+fi
+
+# Check if BOOT1_MARKER is in boot_map/trace (indicates second boot)
+if grep -q "BOOT1_MARKER" "$TRACEDIR/instances/boot_map/trace" 2>/dev/null; then
+	# Second boot: verify BOOT1_MARKER was copied into backup/trace from Boot 1
+	if grep -q "BOOT1_MARKER" "$TRACEDIR/instances/backup/trace" 2>/dev/null; then
+		echo "PASS: persistent-02-backup-instance"
+		exit 0
+	else
+		echo "FAIL: BOOT1_MARKER found in boot_map/trace" \
+			"but missing from backup/trace on second boot"
+		exit 1
+	fi
+fi
+
+# First boot: write BOOT1_MARKER to boot_map and reboot via sysrq-trigger
+echo "BOOT1_MARKER" > "$TRACEDIR/instances/boot_map/trace_marker"
+sync
+
+# Trigger reboot to restart into second boot
+echo b > /proc/sysrq-trigger 2>/dev/null || echo c > /proc/sysrq-trigger 2>/dev/null || true
+sleep 5
+echo "FAIL: reboot trigger failed on first boot"
+exit 1