rv: Add rtapp_pagefault monitor

Userspace real-time applications may have design flaws that they raise
page faults in real-time threads, and thus have unexpected latencies.

Add an linear temporal logic monitor to detect this scenario.

Cc: John Ogness <john.ogness@linutronix.de>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/78fea8a2de6d058241d3c6502c1a92910772b0ed.1752088709.git.namcao@linutronix.de
Reviewed-by: Gabriele Monaco <gmonaco@redhat.com>
Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

1 files changed, 88 insertions, 0 deletions

diff --git a/kernel/trace/rv/monitors/pagefault/pagefault.c b/kernel/trace/rv/monitors/pagefault/pagefault.c
new file mode 100644
index 000000000000..9fe6123b2200
--- /dev/null
+++ b/kernel/trace/rv/monitors/pagefault/pagefault.c
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/ftrace.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/rv.h>
+#include <linux/sched/deadline.h>
+#include <linux/sched/rt.h>
+#include <linux/tracepoint.h>
+#include <rv/instrumentation.h>
+
+#define MODULE_NAME "pagefault"
+
+#include <rv_trace.h>
+#include <trace/events/exceptions.h>
+#include <monitors/rtapp/rtapp.h>
+
+#include "pagefault.h"
+#include <rv/ltl_monitor.h>
+
+static void ltl_atoms_fetch(struct task_struct *task, struct ltl_monitor *mon)
+{
+	/*
+	 * This includes "actual" real-time tasks and also PI-boosted
+	 * tasks. A task being PI-boosted means it is blocking an "actual"
+	 * real-task, therefore it should also obey the monitor's rule,
+	 * otherwise the "actual" real-task may be delayed.
+	 */
+	ltl_atom_set(mon, LTL_RT, rt_or_dl_task(task));
+}
+
+static void ltl_atoms_init(struct task_struct *task, struct ltl_monitor *mon, bool task_creation)
+{
+	if (task_creation)
+		ltl_atom_set(mon, LTL_PAGEFAULT, false);
+}
+
+static void handle_page_fault(void *data, unsigned long address, struct pt_regs *regs,
+			      unsigned long error_code)
+{
+	ltl_atom_pulse(current, LTL_PAGEFAULT, true);
+}
+
+static int enable_pagefault(void)
+{
+	int retval;
+
+	retval = ltl_monitor_init();
+	if (retval)
+		return retval;
+
+	rv_attach_trace_probe("rtapp_pagefault", page_fault_kernel, handle_page_fault);
+	rv_attach_trace_probe("rtapp_pagefault", page_fault_user, handle_page_fault);
+
+	return 0;
+}
+
+static void disable_pagefault(void)
+{
+	rv_detach_trace_probe("rtapp_pagefault", page_fault_kernel, handle_page_fault);
+	rv_detach_trace_probe("rtapp_pagefault", page_fault_user, handle_page_fault);
+
+	ltl_monitor_destroy();
+}
+
+static struct rv_monitor rv_pagefault = {
+	.name = "pagefault",
+	.description = "Monitor that RT tasks do not raise page faults",
+	.enable = enable_pagefault,
+	.disable = disable_pagefault,
+};
+
+static int __init register_pagefault(void)
+{
+	return rv_register_monitor(&rv_pagefault, &rv_rtapp);
+}
+
+static void __exit unregister_pagefault(void)
+{
+	rv_unregister_monitor(&rv_pagefault);
+}
+
+module_init(register_pagefault);
+module_exit(unregister_pagefault);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Nam Cao <namcao@linutronix.de>");
+MODULE_DESCRIPTION("pagefault: Monitor that RT tasks do not raise page faults");