From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9E77FC433E1 for ; Thu, 27 Aug 2020 11:22:50 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5454F22CBB for ; Thu, 27 Aug 2020 11:22:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5454F22CBB Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id BA9856B0028; Thu, 27 Aug 2020 07:22:49 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B32CF6B0029; Thu, 27 Aug 2020 07:22:49 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9FBE16B002A; Thu, 27 Aug 2020 07:22:49 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0037.hostedemail.com [216.40.44.37]) by kanga.kvack.org (Postfix) with ESMTP id 8659B6B0028 for ; Thu, 27 Aug 2020 07:22:49 -0400 (EDT) Received: from smtpin11.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 41BA21E05 for ; Thu, 27 Aug 2020 11:22:49 +0000 (UTC) X-FDA: 77196111258.11.snail44_1108b6e2706c Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin11.hostedemail.com (Postfix) with ESMTP id 11400180F8B81 for ; Thu, 27 Aug 2020 11:22:49 +0000 (UTC) X-HE-Tag: snail44_1108b6e2706c X-Filterd-Recvd-Size: 4457 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf29.hostedemail.com (Postfix) with ESMTP for ; Thu, 27 Aug 2020 11:22:48 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 9DFD211B3; Thu, 27 Aug 2020 04:22:47 -0700 (PDT) Received: from [192.168.1.190] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 84D723F68F; Thu, 27 Aug 2020 04:22:45 -0700 (PDT) Subject: Re: [PATCH 20/35] arm64: mte: Add in-kernel MTE helpers To: Catalin Marinas Cc: Andrey Konovalov , Dmitry Vyukov , kasan-dev@googlegroups.com, Andrey Ryabinin , Alexander Potapenko , Marco Elver , Evgenii Stepanov , Elena Petrova , Branislav Rankov , Kevin Brodsky , Will Deacon , Andrew Morton , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <2cf260bdc20793419e32240d2a3e692b0adf1f80.1597425745.git.andreyknvl@google.com> <20200827093808.GB29264@gaia> <588f3812-c9d0-8dbe-fce2-1ea89f558bd2@arm.com> <20200827111027.GJ29264@gaia> From: Vincenzo Frascino Message-ID: <921c4ed0-b5b5-bc01-5418-c52d80f1af59@arm.com> Date: Thu, 27 Aug 2020 12:24:58 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200827111027.GJ29264@gaia> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 11400180F8B81 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 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 8/27/20 12:10 PM, Catalin Marinas wrote: > On Thu, Aug 27, 2020 at 11:31:56AM +0100, Vincenzo Frascino wrote: >> On 8/27/20 10:38 AM, Catalin Marinas wrote: >>> On Fri, Aug 14, 2020 at 07:27:02PM +0200, Andrey Konovalov wrote: >>>> +void * __must_check mte_set_mem_tag_range(void *addr, size_t size, u8 tag) >>>> +{ >>>> + void *ptr = addr; >>>> + >>>> + if ((!system_supports_mte()) || (size == 0)) >>>> + return addr; >>>> + >>>> + tag = 0xF0 | (tag & 0xF); >>>> + ptr = (void *)__tag_set(ptr, tag); >>>> + size = ALIGN(size, MTE_GRANULE_SIZE); >>> >>> I think aligning the size is dangerous. Can we instead turn it into a >>> WARN_ON if not already aligned? At a quick look, the callers of >>> kasan_{un,}poison_memory() already align the size. >> >> The size here is used only for tagging purposes and if we want to tag a >> subgranule amount of memory we end up tagging the granule anyway. Why do you >> think it can be dangerous? > > In principle, I don't like expanding the size unless you are an > allocator. Since this code doesn't control the placement of the object > it was given, a warn seems more appropriate. > That's a good point. Ok, we can change this in a warning. >>>> +/* >>>> + * Assign allocation tags for a region of memory based on the pointer tag >>>> + * x0 - source pointer >>>> + * x1 - size >>>> + * >>>> + * Note: size is expected to be MTE_GRANULE_SIZE aligned >>>> + */ >>>> +SYM_FUNC_START(mte_assign_mem_tag_range) >>>> + /* if (src == NULL) return; */ >>>> + cbz x0, 2f >>>> + /* if (size == 0) return; */ >>> >>> You could skip the cbz here and just document that the size should be >>> non-zero and aligned. The caller already takes care of this check. >> >> I would prefer to keep the check here, unless there is a valid reason, since >> allocate(0) is a viable option hence tag(x, 0) should be as well. The caller >> takes care of it in one place, today, but I do not know where the API will be >> used in future. > > That's why I said just document it in the comment above the function. > > The check is also insufficient if the size is not aligned to an MTE > granule, so it's not really consistent. This function should end with a > subs followed by b.gt as cbnz will get stuck in a loop for unaligned > size. > That's correct. Thanks for pointing this out. I currently used it only in places where the caller took care to align the size. But in future we cannot know hence we should harden the function with what you are suggesting. -- Regards, Vincenzo