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From: Alexander Potapenko <>
Cc:,,,,,,, Alexander Potapenko <>
Subject: [PATCH v4 2/2] kfence: skip all GFP_ZONEMASK allocations
Date: Wed, 30 Jun 2021 17:02:34 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Allocation requests outside ZONE_NORMAL (MOVABLE, HIGHMEM or DMA) cannot
be fulfilled by KFENCE, because KFENCE memory pool is located in a
zone different from the requested one.

Because callers of kmem_cache_alloc() may actually rely on the
allocation to reside in the requested zone (e.g. memory allocations done
with __GFP_DMA must be DMAable), skip all allocations done with
GFP_ZONEMASK and/or respective SLAB flags (SLAB_CACHE_DMA and

Fixes: 0ce20dd84089 ("mm: add Kernel Electric-Fence infrastructure")
Cc: Andrew Morton <>
Cc: Dmitry Vyukov <>
Cc: Marco Elver <>
Cc: Greg Kroah-Hartman <>
Cc: Souptick Joarder <>
Cc: # 5.12+
Signed-off-by: Alexander Potapenko <>
Reviewed-by: Marco Elver <>


 - added parentheses around the GFP clause, as requested by Marco
 - ignore GFP_ZONEMASK, which also covers __GFP_HIGHMEM and __GFP_MOVABLE
 - move the flag check at the beginning of the function, as requested by
   Souptick Joarder
 - minor fixes to description and comment formatting
 mm/kfence/core.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 33bb20d91bf6a..1cbdb62e6d0fb 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -740,6 +740,15 @@ void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags)
 	if (size > PAGE_SIZE)
 		return NULL;
+	/*
+	 * Skip allocations from non-default zones, including DMA. We cannot
+	 * guarantee that pages in the KFENCE pool will have the requested
+	 * properties (e.g. reside in DMAable memory).
+	 */
+	if ((flags & GFP_ZONEMASK) ||
+	    (s->flags & (SLAB_CACHE_DMA | SLAB_CACHE_DMA32)))
+		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

  reply	other threads:[~2021-06-30 15:02 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-30 15:02 [PATCH v4 1/2] kfence: move the size check to the beginning of __kfence_alloc() Alexander Potapenko
2021-06-30 15:02 ` Alexander Potapenko [this message]
2021-07-05 14:05   ` [PATCH v4 2/2] kfence: skip all GFP_ZONEMASK allocations Marco Elver
2021-07-13 16:19     ` Marco Elver
2021-07-05 18:38   ` Souptick Joarder

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