From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 43F7144E64F; Mon, 21 Sep 2026 07:58:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789977506; cv=none; b=EeB5xtFcW/2zNN2vSEn46Z+iXK+QKe4zhBxvR/m6eLKViJoaZjnDZ4qno0AaqvNb91lcBnchOX6xSAn2M7+0BCGyEMIjqkkvt6pxYSp4Irigq2UA63e0i6DUkgI2PmseuVS8d6hyH8pkrjF5G3r36AcO56DHUT8ysFS981GJxFo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789977506; c=relaxed/simple; bh=JttRvJ5Bt7Z1wv5k3OeZaQLY1XifIpQ6GOQSBGFqk9c=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=mfBlKtZtSA9Nm+Yrr5lwzNorxg+6MTXO4VRCjqPKncxPm3LB8RR2P+Nc92bL98p2LB2wEUrj7Mci513sN7C93D9LFizAIeJsi7TOMCePMx1n0B0cBL1lRT3mPxqpRGLgmSU0Zb/YFVPDHEFXohmmAXziwBcFpRIruc7I/niOLIQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=F7gaLOOy; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="F7gaLOOy" Received: by smtp.kernel.org (Postfix) with ESMTPSA id ADF991F0089F; Mon, 21 Sep 2026 07:58:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789977500; bh=yijECeyPSWNw4ynQbXuj4ormaGJLP5eNf5p0NnJNYTA=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=F7gaLOOyxLvwBiW7gSUta9X63c8Dgm/E8HGRTY2VHCQMCjFT/ne11cizs+X+lvWkG wX1KjpOQEm+9px1QueJc++e57qYKlyBU9gfNJ/OnikvetwQJbBfgovwi/TYYvlSyYT s+Q39M9FmFVZJKK2GA7JYy+8Zz/vsJI5AjF6joWESIutRegzES931DIQ1J47nZE6Zm oDYYtzbpGB3Gyi4+f7vp2e4FbaWzWCyfS1mNPJWuAXvHKJ6HyX1fo/SqyJzTgCxk9E mOQe/tKjsAHoRk7mMrUxL3fOXIhZGF/4he05kJ1a86y6olq9/s3BVPdjhFxOUuClPD m6RNtXsEiz+VQ== From: Kees Cook To: Vlastimil Babka Cc: Kees Cook , Harry Yoo , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , linux-mm@kvack.org, Pedro Falcato , Kuniyuki Iwashima , linux-hardening@vger.kernel.org, Jakub Kicinski , "David S. Miller" , Eric Dumazet , Paolo Abeni , Simon Horman , Jason Xing , =?UTF-8?q?Bj=C3=B6rn=20T=C3=B6pel?= , Jiayuan Chen , Willem de Bruijn , linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: [PATCH v4 5/7] mm/slab: Provide kmalloc type fallback for bucket allocations Date: Mon, 21 Sep 2026 00:58:16 -0700 Message-Id: <20260921075820.1718334-5-kees@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260921075811.too.775-kees@kernel.org> References: <20260921075811.too.775-kees@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=6106; i=kees@kernel.org; h=from:subject; bh=JttRvJ5Bt7Z1wv5k3OeZaQLY1XifIpQ6GOQSBGFqk9c=; b=owGbwMvMwCVmps19z/KJym7G02pJDFkbHs906rW+v3eOw4TVFQofjDkNs+Xbee77upmkZh9NU T2y7pJYRykLgxgXg6yYIkuQnXuci8fb9nD3uYowc1iZQIYwcHEKwETCOBj+x/c9ThZ6eXPZWZMJ qx8J/r41+aG0x+EkdlaPxb5G3Bo3pRkZ9py0ZZ9T75xktja5xzL9Tojb0ektIf16vUxb6gu3Kv3 gAQA= X-Developer-Key: i=kees@kernel.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Content-Transfer-Encoding: 8bit kmem_buckets_create() clones kmalloc_caches[KMALLOC_NORMAL]. kmalloc_slab() figures out the kmalloc type the caller asks for, but then ignored it whenever a bucket set was in use, returning a normal cache regardless. This would be a problem if a caller asked for GFP_DMA, __GFP_ACCOUNT, etc. None of the current users do this, so there is problem, but it makes adding new users fragile. For example, skb data[1] needs to handle GFP_DMA (rarely) and __GFP_ACCOUNT (often). Send those allocations to the general caches instead so nothing breaks and regular allocations remain isolated with the bucket. The kmem_bucket_type enum contains only a single item here, but will be expanded in the next patch. Built and tests pass with ARCH=x86_64 defconfig with GCC 16.2.0, with CONFIG_SLAB_BUCKETS as y and n. Assisted-by: LLM Link: https://lore.kernel.org/all/04debe19-bbe8-4b5f-9668-753d1f97832d@redhat.com/ [1] Signed-off-by: Kees Cook --- Cc: Vlastimil Babka Cc: Harry Yoo Cc: Andrew Morton Cc: Hao Li Cc: Christoph Lameter Cc: David Rientjes Cc: Roman Gushchin Cc: Cc: Pedro Falcato Cc: Kuniyuki Iwashima Cc: --- include/linux/slab.h | 13 +++++++++++ mm/slab.h | 23 ++++++++++++++++-- lib/tests/slub_kunit.c | 53 ++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 87 insertions(+), 2 deletions(-) diff --git a/include/linux/slab.h b/include/linux/slab.h index 18a2351f9084..ab9ab3d34847 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -742,6 +742,19 @@ typedef struct kmem_cache * kmem_buckets[KMALLOC_SHIFT_HIGH + 1]; extern kmem_buckets kmalloc_caches[NR_KMALLOC_TYPES]; +/* + * The kmalloc types a bucket set can hold a copy of. This is deliberately not + * enum kmalloc_cache_type: the KMALLOC_PARTITION copies are all "normal" to a + * bucket set, which already separates what they were there to separate, so + * indexing by those would mean up to KMALLOC_PARTITION_CACHES_NR unusable + * rows per set. Allocations of any type not listed here are served by the + * general caches. + */ +enum kmem_bucket_type { + KMEM_BUCKET_NORMAL = 0, + NR_KMEM_BUCKET_TYPES +}; + /* * Define gfp bits that should not be set for KMALLOC_NORMAL. */ diff --git a/mm/slab.h b/mm/slab.h index 8fd6835e4235..7f1bfee83b92 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -421,6 +421,26 @@ static inline unsigned int size_index_elem(unsigned int bytes) return (bytes - 1) / 8; } +/* + * Which set of buckets to use for the given kmalloc_cache_type. If not + * handled by the kmem_buckets, fall back to general caches. + */ +static inline kmem_buckets * +kmalloc_choose_bucket(kmem_buckets *bucket, enum kmalloc_cache_type type) +{ + enum kmem_bucket_type btype; + + if (!bucket) + return &kmalloc_caches[type]; + + if (type <= KMALLOC_PARTITION_END) + btype = KMEM_BUCKET_NORMAL; + else + return &kmalloc_caches[type]; /* No set holds a row for it. */ + + return &bucket[btype]; +} + /* * Find the kmem_cache structure that serves a given size of * allocation @@ -438,8 +458,7 @@ kmalloc_slab(size_t size, kmem_buckets *b, gfp_t flags, kmalloc_token_t token, if (alloc_flags & SLAB_ALLOC_NO_OBJ_EXT) type = KMALLOC_NO_OBJ_EXT; - if (!b) - b = &kmalloc_caches[type]; + b = kmalloc_choose_bucket(b, type); if (size <= 192) index = kmalloc_size_index[size_index_elem(size)]; else diff --git a/lib/tests/slub_kunit.c b/lib/tests/slub_kunit.c index d6467dd5cf9b..823607e06248 100644 --- a/lib/tests/slub_kunit.c +++ b/lib/tests/slub_kunit.c @@ -683,6 +683,58 @@ static void test_kmem_buckets_destroy(struct kunit *test) KUNIT_EXPECT_EQ(test, 2, slab_errors); } +/* + * A bucket set holds only the kmalloc types it was created with, so an + * allocation that asks for a different one has to come from the general + * caches. Check that it does, rather than being served a normal cache that + * does not satisfy what the flags asked for. + */ +static void test_kmem_buckets_type_fallback(struct kunit *test) +{ + struct kmem_cache *c; + kmem_buckets *b; + void *p; + + if (!IS_ENABLED(CONFIG_SLAB_BUCKETS)) + kunit_skip(test, "needs CONFIG_SLAB_BUCKETS"); + + b = kmem_buckets_create("test_buckets", 0, 0, INT_MAX, NULL); + KUNIT_ASSERT_BUCKETS_CREATED(test, b); + + /* A plain allocation stays isolated in the bucket set. */ + p = kmem_buckets_alloc(b, 128, GFP_KERNEL); + KUNIT_ASSERT_NOT_NULL(test, p); + c = cache_of(p); + kfree(p); + KUNIT_ASSERT_NOT_NULL(test, c); + + KUNIT_EXPECT_TRUE_MSG(test, strstarts(c->name, "test_buckets-"), + "expected a bucket cache, got %s", c->name); + + /* One that needs ZONE_DMA cannot, so it falls back. */ + if (IS_ENABLED(CONFIG_ZONE_DMA)) { + p = kmem_buckets_alloc(b, 128, GFP_KERNEL | GFP_DMA); + KUNIT_ASSERT_NOT_NULL(test, p); + c = cache_of(p); + kfree(p); + KUNIT_ASSERT_NOT_NULL(test, c); + + KUNIT_EXPECT_TRUE_MSG(test, strstarts(c->name, "dma-kmalloc-"), + "expected a DMA cache, got %s", c->name); + } + + /* Nor can one that has to be accounted. */ + if (IS_ENABLED(CONFIG_MEMCG) && !mem_cgroup_kmem_disabled()) { + p = kmem_buckets_alloc(b, 128, GFP_KERNEL | __GFP_ACCOUNT); + KUNIT_ASSERT_NOT_NULL(test, p); + c = virt_to_slab(p)->slab_cache; + kfree(p); + + KUNIT_EXPECT_TRUE_MSG(test, strstarts(c->name, "kmalloc-cg-"), + "expected an accounted cache, got %s", c->name); + } +} + static struct kunit_case test_cases[] = { KUNIT_CASE(test_clobber_zone), @@ -709,6 +761,7 @@ static struct kunit_case test_cases[] = { KUNIT_CASE(test_kmem_buckets_alignment), KUNIT_CASE(test_kmem_buckets_disabled), KUNIT_CASE(test_kmem_buckets_destroy), + KUNIT_CASE(test_kmem_buckets_type_fallback), {} }; -- 2.34.1