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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=VaCIY3e1mM/3lajYRe+4kEeATPJjHgU8XC8DGOZ/gGNs4k32VM9U6XL3g1QNFwMX7 aiE1mChsAlQuWiG6dtlqRE2QG1uwezLRN5eWNRz4nneCDgGMRgbFGO85Pk32T8U+pL 1qRkiXei4Y3UKQbNxNmYYSp43V/UdA6VLpVX9moM= Message-ID: <794cc60f-4d51-40e3-9e06-4848d05a0f07@arm.com> Date: Thu, 14 May 2026 15:52:43 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/3] kasan: hw_tags: some micro-optimizations To: "Harry Yoo (Oracle)" Cc: akpm@linux-foundation.org, vbabka@kernel.org, ryabinin.a.a@gmail.com, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, hao.li@linux.dev, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, glider@google.com, andreyknvl@gmail.com, dvyukov@google.com, vincenzo.frascino@arm.com, kasan-dev@googlegroups.com, ryan.roberts@arm.com, anshuman.khandual@arm.com, catalin.marinas@arm.com References: <20260513105734.3380544-1-dev.jain@arm.com> Content-Language: en-US From: Dev Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: ABA831C0010 X-Rspam-User: X-Stat-Signature: jsm7xqd54en94rw4mpp4rnp9ewbg8uj8 X-HE-Tag: 1778754183-595365 X-HE-Meta: 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 pqaNhugp uwvAJVD0ydmyzqg6FUoKNH6xsUyH/jLdRrSgPDTtyvzNd7aRa3kXt+pC74FFdDkgtEVQihdyUm/6qzJLM0P5LbUjbu3EDB8CoewyJkjbtMt8rUNTAS/7yoGrSfKGaa8oRtt8btvuBCB4itp5SFBOrWIJeDrggPFqAAD0Xs2+Iu7Uhip6ZCfrSicjIb/nMKpkC6u8iyng5tVsHdF5oxyjTyWBpfDjXoyEkXL0j7/NOWWUbS9lHHODSRDQUeVjgkQlmnZ7LsvE1DOG2sA/9UJudHRCkZJdbYL3vMoXLZn6ao3WDxJx216FbgvOtGtq/2gdlMJOfZgVoAedLapE8KDtDspt4/T/MgavwMifn Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 14/05/26 3:26 pm, Harry Yoo (Oracle) wrote: > I have a few questions... > > Does the performance of KASAN_HW_TAGS matter? > > Yes, the performance of Hardware Tag-Based KASAN matters because > it is meant to be used in production on mobile devices as it utilizes > cutting-edge (to me) hardware support instead of compiler > instrumentation. > > Do you have data or are you planning to measure the performance > impact of this work? I will get back on this. > > On Wed, May 13, 2026 at 04:27:31PM +0530, Dev Jain wrote: >> Patch 1 uses GFP_SKIP_KASAN to skip unpoisoning of a slab page in the page >> allocator, since slab allocator itself poisons the slab page immediately. > > If __GFP_SKIP_KASAN skips unpoisoning, why should the slab allocator > poison the whole page (kasan_poison_slab())? It's already poisoned. Nice observation! Although it may not always be the case that the slab page is already poisoned. If should_skip_kasan_poison() in the buddy code triggers, then a freed page is not poisoned. But, the point of kasan_poison_slab() is still served without it - an OOB for a slab object is still caught probabilistically because the allocation has a random tag. > >> Patch 2 and 3 remove wasted work while poisoning the tail end of the >> vmalloc/slab allocation. > >> --- >> Based on 7.1-rc2. >> >> Dev Jain (3): >> mm/slub: hw_tags: skip page-allocator unpoisoning on slab allocation >> kasan: avoid re-poisoning tag-based kmalloc redzones >> vmalloc: hw_tags: optimize vmalloc redzoning >> >> include/linux/kasan.h | 17 +++++++++---- >> mm/kasan/common.c | 55 +++++++++++++++++++++++++++++++++---------- >> mm/kasan/hw_tags.c | 13 ++++++---- >> mm/page_alloc.c | 2 +- >> mm/slub.c | 22 ++++++++++++----- >> 5 files changed, 79 insertions(+), 30 deletions(-) >> >> -- >> 2.43.0 >> >