Allow the use of a deferrable timer, which does not force CPU wake-ups
when the system is idle. A consequence is that the sample interval
becomes very unpredictable, to the point that it is not guaranteed that
the KFENCE KUnit test still passes.
Nevertheless, on power-constrained systems this may be preferable, so
let's give the user the option should they accept the above trade-off.
Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
---
lib/Kconfig.kfence | 12 ++++++++++++
mm/kfence/core.c | 15 +++++++++++++--
2 files changed, 25 insertions(+), 2 deletions(-)
diff --git a/lib/Kconfig.kfence b/lib/Kconfig.kfence
index 912f252a41fc..1cf2ea2a1ac7 100644
--- a/lib/Kconfig.kfence
+++ b/lib/Kconfig.kfence
@@ -45,6 +45,18 @@ config KFENCE_NUM_OBJECTS
pages are required; with one containing the object and two adjacent
ones used as guard pages.
+config KFENCE_DEFERRABLE
+ bool "Use a deferrable timer to trigger allocations" if EXPERT
+ help
+ Use a deferrable timer to trigger allocations. This avoids forcing
+ CPU wake-ups if the system is idle, at the risk of a less predictable
+ sample interval.
+
+ Warning: The KUnit test suite fails with this option enabled - due to
+ the unpredictability of the sample interval!
+
+ Say N if you are unsure.
+
config KFENCE_STATIC_KEYS
bool "Use static keys to set up allocations" if EXPERT
depends on JUMP_LABEL
diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index f126b53b9b85..451277b41bfb 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -95,6 +95,10 @@ module_param_cb(sample_interval, &sample_interval_param_ops, &kfence_sample_inte
static unsigned long kfence_skip_covered_thresh __read_mostly = 75;
module_param_named(skip_covered_thresh, kfence_skip_covered_thresh, ulong, 0644);
+/* If true, use a deferrable timer at the risk of unpredictable sample intervals. */
+static bool kfence_deferrable __read_mostly = IS_ENABLED(CONFIG_KFENCE_DEFERRABLE);
+module_param_named(deferrable, kfence_deferrable, bool, 0444);
+
/* The pool of pages used for guard pages and objects. */
char *__kfence_pool __read_mostly;
EXPORT_SYMBOL(__kfence_pool); /* Export for test modules. */
@@ -740,6 +744,8 @@ late_initcall(kfence_debugfs_init);
/* === Allocation Gate Timer ================================================ */
+static struct delayed_work kfence_timer;
+
#ifdef CONFIG_KFENCE_STATIC_KEYS
/* Wait queue to wake up allocation-gate timer task. */
static DECLARE_WAIT_QUEUE_HEAD(allocation_wait);
@@ -762,7 +768,6 @@ static DEFINE_IRQ_WORK(wake_up_kfence_timer_work, wake_up_kfence_timer);
* avoids IPIs, at the cost of not immediately capturing allocations if the
* instructions remain cached.
*/
-static struct delayed_work kfence_timer;
static void toggle_allocation_gate(struct work_struct *work)
{
if (!READ_ONCE(kfence_enabled))
@@ -790,7 +795,6 @@ static void toggle_allocation_gate(struct work_struct *work)
queue_delayed_work(system_unbound_wq, &kfence_timer,
msecs_to_jiffies(kfence_sample_interval));
}
-static DECLARE_DELAYED_WORK(kfence_timer, toggle_allocation_gate);
/* === Public interface ===================================================== */
@@ -809,8 +813,15 @@ static void kfence_init_enable(void)
{
if (!IS_ENABLED(CONFIG_KFENCE_STATIC_KEYS))
static_branch_enable(&kfence_allocation_key);
+
+ if (kfence_deferrable)
+ INIT_DEFERRABLE_WORK(&kfence_timer, toggle_allocation_gate);
+ else
+ INIT_DELAYED_WORK(&kfence_timer, toggle_allocation_gate);
+
WRITE_ONCE(kfence_enabled, true);
queue_delayed_work(system_unbound_wq, &kfence_timer, 0);
+
pr_info("initialized - using %lu bytes for %d objects at 0x%p-0x%p\n", KFENCE_POOL_SIZE,
CONFIG_KFENCE_NUM_OBJECTS, (void *)__kfence_pool,
(void *)(__kfence_pool + KFENCE_POOL_SIZE));
--
2.35.1.616.g0bdcbb4464-goog
