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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=P9xMpzZA3w4Ud4GhNZYAR7rMtLEydQwCTF5BmTXmZvPjLCv1UXfUP8+r8Iq8CbCLQ nRrOkqVf1Wr8M0pq84KEAZLTFtdvS80erxNi0JgM/Kw6LvYGCLadma1qHOiO2oStX9 L5zWdZrvA5KAhMLYETPu4C+RFIalR3vIj8I+cxO0= Message-ID: <7b4f284c-9659-4422-a452-e67dcbfb0140@arm.com> Date: Fri, 19 Jun 2026 10:14:33 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 2/2] kasan: hw_tags: Add boot option to elide free time poisoning To: Isaac Manjarres Cc: ryabinin.a.a@gmail.com, akpm@linux-foundation.org, corbet@lwn.net, glider@google.com, andreyknvl@gmail.com, dvyukov@google.com, vincenzo.frascino@arm.com, kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, skhan@linuxfoundation.org, workflows@vger.kernel.org, linux-doc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, kaleshsingh@google.com, 21cnbao@gmail.com, david@kernel.org, will@kernel.org, catalin.marinas@arm.com References: <20260612044425.763060-1-dev.jain@arm.com> <20260612044425.763060-3-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: rspam03 X-Rspamd-Queue-Id: 8A4161C000B X-Stat-Signature: sxncr7oq3iw5uoiyd5mr4uxjuh1mozio X-Rspam-User: X-HE-Tag: 1781844290-697287 X-HE-Meta: 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 Ve5J6i7M hINt/umTz5cULlKMlm8e5VTydNwX3d3jDBNR4eluT0qeiw1JXnqVNXby0k9BfFd9zyoZf8y1/1litrODxXmHeBVZO0kBJBapcDya0u2d4EjDEDMkq8xVXdjjhKOkV2Ne3mxwqtl2Z1zGfcpppV5tc8b4oF/wRGjUFVAdoJqUVt9/6xJkmiuxgpH7ZD410SkOyTruzQHSiKReWcVGYkJhZyvPcsVD0Vx5hrgYHqDF8XZYmMwUC1TIIL1BGtWT0ZZ/FHT2IcYZV1lvrMEhyegvcDObqWvZxAyC9SxC4XTwyoAykK2U1Kg1WGN23xWAzfUYIPmvP2+BbhF2m6KRxFcqZeTDvMlqLQlfRF1Icd1C7ImJEZlo= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 13/06/26 5:53 am, Isaac Manjarres wrote: > On Fri, Jun 12, 2026 at 04:44:24AM +0000, Dev Jain wrote: >> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h >> index fc9169a547662..4fa8abb312faa 100644 >> --- a/mm/kasan/kasan.h >> +++ b/mm/kasan/kasan.h >> #ifdef CONFIG_KASAN_GENERIC >> @@ -478,6 +489,16 @@ static inline u8 kasan_random_tag(void) { return 0; } >> >> static inline void kasan_poison(const void *addr, size_t size, u8 value, bool init) >> { >> + if (kasan_tag_only_on_alloc_enabled()) { >> + if ((value != KASAN_SLAB_REDZONE) && (value != KASAN_PAGE_REDZONE)) { >> + if (init) >> + memset((void *)kasan_reset_tag(addr), 0, size); >> + return; >> + } >> + } >> + >> + value |= 0xF0; >> + > > I wonder if it would make more sense to have this as: > > if (kasan_tag_only_on_alloc_enabled() && (value == KASAN_SLAB_FREE || > value == KASAN_PAGE_FREE)) { > if (init) > memset((void *)kasan_reset_tag(addr), 0, size); > return; > } > > That seems a bit clearer to me as to what it is that you're doing, and > also makes it so that you don't have to do any bit manipulation > on the value when you're filling in the redzones. Ah so you mean, we can define KASAN_SLAB_FREE and KASAN_PAGE_FREE to be different values, leaving KASAN_SLAB_REDZONE and KASAN_PAGE_REDZONE to be 0xFE, the poison value. Yep I'll do that. > > Thanks, > Isaac