[PATCH v8 19/22] rv: Add rtapp_pagefault monitor

Nam Cao
2025-05-12T10:51:22Z

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.

Reviewed-by: Gabriele Monaco <gmonaco@redhat.com>
Signed-off-by: Nam Cao <namcao@linutronix.de>
---
kernel/trace/rv/Kconfig | 1 +
kernel/trace/rv/Makefile | 1 +
kernel/trace/rv/monitors/pagefault/Kconfig | 11 +++
.../trace/rv/monitors/pagefault/pagefault.c | 87 +++++++++++++++++++
.../trace/rv/monitors/pagefault/pagefault.h | 57 ++++++++++++
.../rv/monitors/pagefault/pagefault_trace.h | 14 +++
kernel/trace/rv/rv_trace.h | 1 +
tools/verification/models/rtapp/pagefault.ltl | 1 +
8 files changed, 173 insertions(+)
create mode 100644 kernel/trace/rv/monitors/pagefault/Kconfig
create mode 100644 kernel/trace/rv/monitors/pagefault/pagefault.c
create mode 100644 kernel/trace/rv/monitors/pagefault/pagefault.h
create mode 100644 kernel/trace/rv/monitors/pagefault/pagefault_trace.h
create mode 100644 tools/verification/models/rtapp/pagefault.ltl

diff --git a/kernel/trace/rv/Kconfig b/kernel/trace/rv/Kconfig
index 5c407d291661..6f86d8501e87 100644
--- a/kernel/trace/rv/Kconfig
+++ b/kernel/trace/rv/Kconfig
@@ -42,6 +42,7 @@ source "kernel/trace/rv/monitors/scpd/Kconfig"
source "kernel/trace/rv/monitors/snep/Kconfig"
source "kernel/trace/rv/monitors/sncid/Kconfig"
source "kernel/trace/rv/monitors/rtapp/Kconfig"
+source "kernel/trace/rv/monitors/pagefault/Kconfig"
# Add new monitors here

config RV_REACTORS
diff --git a/kernel/trace/rv/Makefile b/kernel/trace/rv/Makefile
index 9b28c2419995..353ecf939d0e 100644
--- a/kernel/trace/rv/Makefile
+++ b/kernel/trace/rv/Makefile
@@ -13,6 +13,7 @@ obj-$(CONFIG_RV_MON_SCPD) += monitors/scpd/scpd.o
obj-$(CONFIG_RV_MON_SNEP) += monitors/snep/snep.o
obj-$(CONFIG_RV_MON_SNCID) += monitors/sncid/sncid.o
obj-$(CONFIG_RV_MON_RTAPP) += monitors/rtapp/rtapp.o
+obj-$(CONFIG_RV_MON_PAGEFAULT) += monitors/pagefault/pagefault.o
# Add new monitors here
obj-$(CONFIG_RV_REACTORS) += rv_reactors.o
obj-$(CONFIG_RV_REACT_PRINTK) += reactor_printk.o
diff --git a/kernel/trace/rv/monitors/pagefault/Kconfig b/kernel/trace/rv/monitors/pagefault/Kconfig
new file mode 100644
index 000000000000..b31dee208459
--- /dev/null
+++ b/kernel/trace/rv/monitors/pagefault/Kconfig
@@ -0,0 +1,11 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+config RV_MON_PAGEFAULT
+ depends on RV
+ select RV_LTL_MONITOR
+ depends on RV_MON_RTAPP
+ default y
+ select LTL_MON_EVENTS_ID
+ bool "pagefault monitor"
+ help
+ Monitor that real-time tasks do not raise page faults
diff --git a/kernel/trace/rv/monitors/pagefault/pagefault.c b/kernel/trace/rv/monitors/pagefault/pagefault.c
new file mode 100644
index 000000000000..80f6d7ecf5cf
--- /dev/null
+++ b/kernel/trace/rv/monitors/pagefault/pagefault.c
@@ -0,0 +1,87 @@
+// 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");
diff --git a/kernel/trace/rv/monitors/pagefault/pagefault.h b/kernel/trace/rv/monitors/pagefault/pagefault.h
new file mode 100644
index 000000000000..94c0fe4fdaa5
--- /dev/null
+++ b/kernel/trace/rv/monitors/pagefault/pagefault.h
@@ -0,0 +1,57 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <linux/rv.h>
+
+#define MONITOR_NAME pagefault
+
+enum ltl_atom {
+ LTL_PAGEFAULT,
+ LTL_RT,
+ LTL_NUM_ATOM
+};
+static_assert(LTL_NUM_ATOM <= RV_MAX_LTL_ATOM);
+
+static const char *ltl_atom_str(enum ltl_atom atom)
+{
+ static const char *const names[] = {
+ "pa",
+ "rt",
+ };
+
+ return names[atom];
+}
+
+enum ltl_buchi_state {
+ S0,
+ RV_NUM_BA_STATES
+};
+static_assert(RV_NUM_BA_STATES <= RV_MAX_BA_STATES);
+
+static void ltl_start(struct task_struct *task, struct ltl_monitor *mon)
+{
+ bool pagefault = test_bit(LTL_PAGEFAULT, mon->atoms);
+ bool val3 = !pagefault;
+ bool rt = test_bit(LTL_RT, mon->atoms);
+ bool val1 = !rt;
+ bool val4 = val1 || val3;
+
+ if (val4)
+ __set_bit(S0, mon->states);
+}
+
+static void
+ltl_possible_next_states(struct ltl_monitor *mon, unsigned int state, unsigned long *next)
+{
+ bool pagefault = test_bit(LTL_PAGEFAULT, mon->atoms);
+ bool val3 = !pagefault;
+ bool rt = test_bit(LTL_RT, mon->atoms);
+ bool val1 = !rt;
+ bool val4 = val1 || val3;
+
+ switch (state) {
+ case S0:
+ if (val4)
+ __set_bit(S0, next);
+ break;
+ }
+}
diff --git a/kernel/trace/rv/monitors/pagefault/pagefault_trace.h b/kernel/trace/rv/monitors/pagefault/pagefault_trace.h
new file mode 100644
index 000000000000..fe1f82597b1a
--- /dev/null
+++ b/kernel/trace/rv/monitors/pagefault/pagefault_trace.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Snippet to be included in rv_trace.h
+ */
+
+#ifdef CONFIG_RV_MON_PAGEFAULT
+DEFINE_EVENT(event_ltl_monitor_id, event_pagefault,
+ TP_PROTO(struct task_struct *task, char *states, char *atoms, char *next),
+ TP_ARGS(task, states, atoms, next));
+DEFINE_EVENT(error_ltl_monitor_id, error_pagefault,
+ TP_PROTO(struct task_struct *task),
+ TP_ARGS(task));
+#endif /* CONFIG_RV_MON_PAGEFAULT */
diff --git a/kernel/trace/rv/rv_trace.h b/kernel/trace/rv/rv_trace.h
index 12fe926ea853..cfa34af5551b 100644
--- a/kernel/trace/rv/rv_trace.h
+++ b/kernel/trace/rv/rv_trace.h
@@ -172,6 +172,7 @@ TRACE_EVENT(error_ltl_monitor_id,

TP_printk("%s[%d]: violation detected", __get_str(comm), __entry->pid)
);
+#include <monitors/pagefault/pagefault_trace.h>
// Add new monitors based on CONFIG_LTL_MON_EVENTS_ID here
#endif /* CONFIG_LTL_MON_EVENTS_ID */
#endif /* _TRACE_RV_H */
diff --git a/tools/verification/models/rtapp/pagefault.ltl b/tools/verification/models/rtapp/pagefault.ltl
new file mode 100644
index 000000000000..d7ce62102733
--- /dev/null
+++ b/tools/verification/models/rtapp/pagefault.ltl
@@ -0,0 +1 @@
+RULE = always (RT imply not PAGEFAULT)
--
2.39.5