5.15-stable review patch. If anyone has any objections, please let me know.
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From: Marco Elver elver@google.com
[ Upstream commit 737b6a10ac19e41877aa1911bf6b361a72a88ad9 ]
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.
Link: https://lkml.kernel.org/r/20220308141415.3168078-1-elver@google.com Signed-off-by: Marco Elver elver@google.com Reviewed-by: Alexander Potapenko glider@google.com Cc: Dmitry Vyukov dvyukov@google.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Stable-dep-of: e64f81946adf ("kfence: skip __GFP_THISNODE allocations on NUMA systems") Signed-off-by: Sasha Levin sashal@kernel.org --- Documentation/dev-tools/kfence.rst | 12 ++++++++++++ lib/Kconfig.kfence | 12 ++++++++++++ mm/kfence/core.c | 15 +++++++++++++-- 3 files changed, 37 insertions(+), 2 deletions(-)
diff --git a/Documentation/dev-tools/kfence.rst b/Documentation/dev-tools/kfence.rst index 48244d32780f6..b6671d907836a 100644 --- a/Documentation/dev-tools/kfence.rst +++ b/Documentation/dev-tools/kfence.rst @@ -41,6 +41,18 @@ guarded by KFENCE. The default is configurable via the Kconfig option ``CONFIG_KFENCE_SAMPLE_INTERVAL``. Setting ``kfence.sample_interval=0`` disables KFENCE.
+The sample interval controls a timer that sets up KFENCE allocations. By +default, to keep the real sample interval predictable, the normal timer also +causes CPU wake-ups when the system is completely idle. This may be undesirable +on power-constrained systems. The boot parameter ``kfence.deferrable=1`` +instead switches to a "deferrable" timer which does not force CPU wake-ups on +idle systems, at the risk of unpredictable sample intervals. The default is +configurable via the Kconfig option ``CONFIG_KFENCE_DEFERRABLE``. + +.. warning:: + The KUnit test suite is very likely to fail when using a deferrable timer + since it currently causes very unpredictable sample intervals. + The KFENCE memory pool is of fixed size, and if the pool is exhausted, no further KFENCE allocations occur. With ``CONFIG_KFENCE_NUM_OBJECTS`` (default 255), the number of available guarded objects can be controlled. Each object diff --git a/lib/Kconfig.kfence b/lib/Kconfig.kfence index 912f252a41fc6..459dda9ef619b 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" + 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 3eab72fb3d8c9..1a2dc187a72f9 100644 --- a/mm/kfence/core.c +++ b/mm/kfence/core.c @@ -89,6 +89,10 @@ 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. */ +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 __ro_after_init; EXPORT_SYMBOL(__kfence_pool); /* Export for test modules. */ @@ -695,6 +699,8 @@ 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); @@ -717,7 +723,6 @@ 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)) @@ -745,7 +750,6 @@ 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 ===================================================== */
@@ -774,8 +778,15 @@ void __init kfence_init(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));