linux-kernel - [PATCH v4 2/2] kfence: skip all GFP

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Date:   Wed, 30 Jun 2021 17:02:34 +0200
From:   Alexander Potapenko <glider@...gle.com>
To:     akpm@...ux-foundation.org
Cc:     dvyukov@...gle.com, elver@...gle.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, stable@...r.kernel.org,
        gregkh@...uxfoundation.org, jrdr.linux@...il.com,
        Alexander Potapenko <glider@...gle.com>
Subject: [PATCH v4 2/2] kfence: skip all GFP_ZONEMASK allocations

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
SLAB_CACHE_DMA32).

Fixes: 0ce20dd84089 ("mm: add Kernel Electric-Fence infrastructure")
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Marco Elver <elver@...gle.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Souptick Joarder <jrdr.linux@...il.com>
Cc: stable@...r.kernel.org # 5.12+
Signed-off-by: Alexander Potapenko <glider@...gle.com>
Reviewed-by: Marco Elver <elver@...gle.com>

---

v2:
 - added parentheses around the GFP clause, as requested by Marco
v3:
 - 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
v4:
 - 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
-- 
2.32.0.93.g670b81a890-goog