+ kfence-add-note-to-documentation-about-skipping-covered-allocations.patch added to -mm tree

+ kfence-add-note-to-documentation-about-skipping-covered-allocations.patch added to -mm tree

[akpm]

The patch titled
     Subject: kfence: add note to documentation about skipping covered allocations
has been added to the -mm tree.  Its filename is
     kfence-add-note-to-documentation-about-skipping-covered-allocations.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/kfence-add-note-to-documentation-about-skipping-covered-allocations.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/kfence-add-note-to-documentation-about-skipping-covered-allocations.patch

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------------------------------------------------------
From: Marco Elver <elver@google.com>
Subject: kfence: add note to documentation about skipping covered allocations

Add a note briefly mentioning the new policy about "skipping currently
covered allocations if pool close to full." Since this has a notable
impact on KFENCE's bug-detection ability on systems with large uptimes, it
is worth pointing out the feature.

Link: https://lkml.kernel.org/r/20210923104803.2620285-5-elver@google.com
Signed-off-by: Marco Elver <elver@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Alexander Potapenko <glider@google.com>
Cc: Aleksandr Nogikh <nogikh@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Taras Madan <tarasmadan@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 Documentation/dev-tools/kfence.rst |   11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/Documentation/dev-tools/kfence.rst~kfence-add-note-to-documentation-about-skipping-covered-allocations
+++ a/Documentation/dev-tools/kfence.rst
@@ -269,6 +269,17 @@ tail of KFENCE's freelist, so that the l
 first, and the chances of detecting use-after-frees of recently freed objects
 is increased.
 
+If pool utilization reaches 75% (default) or above, to reduce the risk of the
+pool eventually being fully occupied by allocated objects yet ensure diverse
+coverage of allocations, KFENCE limits currently covered allocations of the
+same source from further filling up the pool. The "source" of an allocation is
+based on its partial allocation stack trace. A side-effect is that this also
+limits frequent long-lived allocations (e.g. pagecache) of the same source
+filling up the pool permanently, which is the most common risk for the pool
+becoming full and the sampled allocation rate dropping to zero. The threshold
+at which to start limiting currently covered allocations can be configured via
+the boot parameter ``kfence.skip_covered_thresh`` (pool usage%).
+
 Interface
 ---------
 
_

Patches currently in -mm which might be from elver@google.com are

kasan-fix-kconfig-check-of-cc_has_working_nosanitize_address.patch
lib-stackdepot-include-gfph.patch
lib-stackdepot-remove-unused-function-argument.patch
lib-stackdepot-introduce-__stack_depot_save.patch
kasan-common-provide-can_alloc-in-kasan_save_stack.patch
kasan-generic-introduce-kasan_record_aux_stack_noalloc.patch
workqueue-kasan-avoid-alloc_pages-when-recording-stack.patch
mm-fix-data-race-in-pagepoisoned.patch
stacktrace-move-filter_irq_stacks-to-kernel-stacktracec.patch
kfence-count-unexpectedly-skipped-allocations.patch
kfence-move-saving-stack-trace-of-allocations-into-__kfence_alloc.patch
kfence-limit-currently-covered-allocations-when-pool-nearly-full.patch
kfence-add-note-to-documentation-about-skipping-covered-allocations.patch