diff options
| -rw-r--r-- | Documentation/dev-tools/kfence.rst | 12 | ||||
| -rw-r--r-- | lib/Kconfig.kfence | 26 |
2 files changed, 23 insertions, 15 deletions
diff --git a/Documentation/dev-tools/kfence.rst b/Documentation/dev-tools/kfence.rst index 0fbe3308bf37..48244d32780f 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 |