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-rw-r--r--Documentation/dev-tools/kfence.rst12
-rw-r--r--lib/Kconfig.kfence26
2 files changed, 23 insertions, 15 deletions
diff --git a/Documentation/dev-tools/kfence.rst b/Documentation/dev-tools/kfence.rst
index d45f952986ae..ac6b89d1a8c3 100644
--- a/Documentation/dev-tools/kfence.rst
+++ b/Documentation/dev-tools/kfence.rst
@@ -231,10 +231,14 @@ Guarded allocations are set up based on the sample interval. After expiration
of the sample interval, the next allocation through the main allocator (SLAB or
SLUB) returns a guarded allocation from the KFENCE object pool (allocation
sizes up to PAGE_SIZE are supported). At this point, the timer is reset, and
-the next allocation is set up after the expiration of the interval. To "gate" a
-KFENCE allocation through the main allocator's fast-path without overhead,
-KFENCE relies on static branches via the static keys infrastructure. The static
-branch is toggled to redirect the allocation to KFENCE.
+the next allocation is set up after the expiration of the interval.
+
+When using ``CONFIG_KFENCE_STATIC_KEYS=y``, KFENCE allocations are "gated"
+through the main allocator's fast-path by relying on static branches via the
+static keys infrastructure. The static branch is toggled to redirect the
+allocation to KFENCE. Depending on sample interval, target workloads, and
+system architecture, this may perform better than the simple dynamic branch.
+Careful benchmarking is recommended.
KFENCE objects each reside on a dedicated page, at either the left or right
page boundaries selected at random. The pages to the left and right of the
diff --git a/lib/Kconfig.kfence b/lib/Kconfig.kfence
index e641add33947..912f252a41fc 100644
--- a/lib/Kconfig.kfence
+++ b/lib/Kconfig.kfence
@@ -25,17 +25,6 @@ menuconfig KFENCE
if KFENCE
-config KFENCE_STATIC_KEYS
- bool "Use static keys to set up allocations"
- default y
- depends on JUMP_LABEL # To ensure performance, require jump labels
- help
- Use static keys (static branches) to set up KFENCE allocations. Using
- static keys is normally recommended, because it avoids a dynamic
- branch in the allocator's fast path. However, with very low sample
- intervals, or on systems that do not support jump labels, a dynamic
- branch may still be an acceptable performance trade-off.
-
config KFENCE_SAMPLE_INTERVAL
int "Default sample interval in milliseconds"
default 100
@@ -56,6 +45,21 @@ config KFENCE_NUM_OBJECTS
pages are required; with one containing the object and two adjacent
ones used as guard pages.
+config KFENCE_STATIC_KEYS
+ bool "Use static keys to set up allocations" if EXPERT
+ depends on JUMP_LABEL
+ help
+ Use static keys (static branches) to set up KFENCE allocations. This
+ option is only recommended when using very large sample intervals, or
+ performance has carefully been evaluated with this option.
+
+ Using static keys comes with trade-offs that need to be carefully
+ evaluated given target workloads and system architectures. Notably,
+ enabling and disabling static keys invoke IPI broadcasts, the latency
+ and impact of which is much harder to predict than a dynamic branch.
+
+ Say N if you are unsure.
+
config KFENCE_STRESS_TEST_FAULTS
int "Stress testing of fault handling and error reporting" if EXPERT
default 0