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Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.0 Subject: Re: [PATCH v2 2/2] mm/slub, kunit: Add a test case for kmalloc redzone check Content-Language: en-US To: Marco Elver Cc: Feng Tang , Andrew Morton , Oliver Glitta , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20221129063358.3012362-1-feng.tang@intel.com> <20221129063358.3012362-2-feng.tang@intel.com> <67e6ebce-f8cc-7d28-5e85-8a3909c2d180@suse.cz> From: Vlastimil Babka In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1669723374; a=rsa-sha256; cv=none; b=0nAHxLbpjEoGzyBtwhFeyPUpSYDgIbiyqaCv2T8Kre9s2Us10/K55zBD5HcC+ly40SIpVm ktYisyLkeb8Dm9Q7tcLKwNczP6kkjHrGWHKp5LPIKVYAGuqv+/Q391r9JzEu+gAJKpvjXC xHz/6cW3h011bc9TptwDtMHhBI7PCtY= ARC-Authentication-Results: i=1; imf12.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=qqpcbvqq; 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dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=UcQe1LxJ; spf=pass (imf12.hostedemail.com: domain of vbabka@suse.cz designates 195.135.220.28 as permitted sender) smtp.mailfrom=vbabka@suse.cz; dmarc=none X-Rspamd-Server: rspam05 X-HE-Tag: 1669723373-96549 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 11/29/22 12:48, Marco Elver wrote: > On Tue, 29 Nov 2022 at 12:01, Vlastimil Babka wrote: >> >> On 11/29/22 10:31, Marco Elver wrote: >> > On Tue, 29 Nov 2022 at 07:37, Feng Tang wrote: > >> For SLAB_SKIP_KFENCE, we could also add the flag after creation to avoid >> this trouble? After all there is a sysfs file to control it at runtime >> anyway (via skip_kfence_store()). >> In that case patch 1 would have to wrap kmem_cache_create() and the flag >> addition with a new function to avoid repeating. That function could also be >> adding SLAB_NO_USER_FLAGS to kmem_cache_create(), instead of the #define >> DEFAULT_FLAGS. > > I wouldn't overcomplicate it, all we need is a way to say "this flag > should not be used directly" - and only have it available via an > indirect step. Availability via sysfs is one such step. > > And for tests, there are 2 options: > > 1. we could provide a function "kmem_cache_set_test_flags(cache, > gfp_flags)" and define SLAB_TEST_FLAGS (which would include > SLAB_SKIP_KFENCE). This still allows to set it generally, but should > make abuse less likely due to the "test" in the name of that function. > > 2. just set it directly, s->flags |= SLAB_SKIP_KFENCE. > > If you're fine with #2, that seems simplest and would be my preference. Yeah, that's what I meant. But slub_kunit.c could still have own internal cache creation function so the "|SLAB_NO_USER_FLAGS" and "s->flags |= SLAB_SKIP_KFENCE" is not repeated X times. > >> For SLAB_KMALLOC there's probably no such way unless we abuse the internal >> APIs even more and call e.g. create_boot_cache() instead of >> kmem_cache_create(). But that one is __init, so probably not. If we do >> instead allow the flag, I wouldn't add it to SLAB_CORE_FLAGS but rather >> SLAB_CACHE_FLAGS and SLAB_FLAGS_PERMITTED. > > I'd probably go with the simplest solution here. Agreed.