+ kfence-move-the-size-check-to-the-beginning-of-__kfence_alloc.patch added to -mm tree

+ kfence-move-the-size-check-to-the-beginning-of-__kfence_alloc.patch added to -mm tree

[akpm]

The patch titled
     Subject: kfence: move the size check to the beginning of __kfence_alloc()
has been added to the -mm tree.  Its filename is
     kfence-move-the-size-check-to-the-beginning-of-__kfence_alloc.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/kfence-move-the-size-check-to-the-beginning-of-__kfence_alloc.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/kfence-move-the-size-check-to-the-beginning-of-__kfence_alloc.patch

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
From: Alexander Potapenko <glider@google.com>
Subject: kfence: move the size check to the beginning of __kfence_alloc()

Check the allocation size before toggling kfence_allocation_gate.  This
way allocations that can't be served by KFENCE will not result in waiting
for another CONFIG_KFENCE_SAMPLE_INTERVAL without allocating anything.

Link: https://lkml.kernel.org/r/20210714092222.1890268-1-glider@google.com
Signed-off-by: Alexander Potapenko <glider@google.com>
Suggested-by: Marco Elver <elver@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: <stable@vger.kernel.org>	[5.12+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/kfence/core.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/mm/kfence/core.c~kfence-move-the-size-check-to-the-beginning-of-__kfence_alloc
+++ a/mm/kfence/core.c
@@ -734,6 +734,13 @@ void kfence_shutdown_cache(struct kmem_c
 void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags)
 {
 	/*
+	 * Perform size check before switching kfence_allocation_gate, so that
+	 * we don't disable KFENCE without making an allocation.
+	 */
+	if (size > PAGE_SIZE)
+		return NULL;
+
+	/*
 	 * allocation_gate only needs to become non-zero, so it doesn't make
 	 * sense to continue writing to it and pay the associated contention
 	 * cost, in case we have a large number of concurrent allocations.
@@ -757,9 +764,6 @@ void *__kfence_alloc(struct kmem_cache *
 	if (!READ_ONCE(kfence_enabled))
 		return NULL;
 
-	if (size > PAGE_SIZE)
-		return NULL;
-
 	return kfence_guarded_alloc(s, size, flags);
 }
 
_

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

kfence-move-the-size-check-to-the-beginning-of-__kfence_alloc.patch
kfence-skip-all-gfp_zonemask-allocations.patch