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=-13.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 2BEB9C433DF for ; Fri, 21 Aug 2020 13:08:27 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 00E01207BB for ; Fri, 21 Aug 2020 13:08:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 00E01207BB Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:48638 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1k96mQ-0007v4-93 for qemu-devel@archiver.kernel.org; Fri, 21 Aug 2020 09:08:26 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:40550) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1k96lU-0007CI-5z for qemu-devel@nongnu.org; Fri, 21 Aug 2020 09:07:28 -0400 Received: from szxga06-in.huawei.com ([45.249.212.32]:56916 helo=huawei.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1k96lQ-0005Td-Od for qemu-devel@nongnu.org; Fri, 21 Aug 2020 09:07:27 -0400 Received: from DGGEMS413-HUB.china.huawei.com (unknown [172.30.72.59]) by Forcepoint Email with ESMTP id B49CDFDF395FBEC6619E; Fri, 21 Aug 2020 21:07:17 +0800 (CST) Received: from [127.0.0.1] (10.174.186.4) by DGGEMS413-HUB.china.huawei.com (10.3.19.213) with Microsoft SMTP Server id 14.3.487.0; Fri, 21 Aug 2020 21:07:09 +0800 Subject: Re: [PATCH v3 05/10] migration/dirtyrate: Record hash results for each sampled page To: "Dr. David Alan Gilbert" , =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= References: <1597634433-18809-1-git-send-email-zhengchuan@huawei.com> <1597634433-18809-6-git-send-email-zhengchuan@huawei.com> <20200820173009.GM2664@work-vm> <20200820175149.GA244434@redhat.com> <20200820175512.GQ2664@work-vm> <95894cf7-ba09-9862-357a-1073a192e934@huawei.com> <20200821123014.GK348677@redhat.com> <20200821123910.GC2655@work-vm> From: Zheng Chuan Message-ID: <5d74c849-e7dd-63c5-db07-3471b3f8183e@huawei.com> Date: Fri, 21 Aug 2020 21:07:09 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200821123910.GC2655@work-vm> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.186.4] X-CFilter-Loop: Reflected Received-SPF: pass client-ip=45.249.212.32; envelope-from=zhengchuan@huawei.com; helo=huawei.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/21 09:07:18 X-ACL-Warn: Detected OS = Linux 3.11 and newer [fuzzy] X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_MSPIKE_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: zhang.zhanghailiang@huawei.com, quintela@redhat.com, linyilu@huawei.com, qemu-devel@nongnu.org, alex.chen@huawei.com, ann.zhuangyanying@huawei.com, fangying1@huawei.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2020/8/21 20:39, Dr. David Alan Gilbert wrote: > * Daniel P. Berrangé (berrange@redhat.com) wrote: >> On Fri, Aug 21, 2020 at 08:22:06PM +0800, Zheng Chuan wrote: >>> >>> >>> On 2020/8/21 1:55, Dr. David Alan Gilbert wrote: >>>> * Daniel P. Berrangé (berrange@redhat.com) wrote: >>>>> On Thu, Aug 20, 2020 at 06:30:09PM +0100, Dr. David Alan Gilbert wrote: >>>>>> * Chuan Zheng (zhengchuan@huawei.com) wrote: >>>>>>> Record hash results for each sampled page. >>>>>>> >>>>>>> Signed-off-by: Chuan Zheng >>>>>>> Signed-off-by: YanYing Zhuang >>>>>>> --- >>>>>>> migration/dirtyrate.c | 144 ++++++++++++++++++++++++++++++++++++++++++++++++++ >>>>>>> migration/dirtyrate.h | 7 +++ >>>>>>> 2 files changed, 151 insertions(+) >>>>>>> >>>>>>> diff --git a/migration/dirtyrate.c b/migration/dirtyrate.c >>>>>>> index c4304ef..62b6f69 100644 >>>>>>> --- a/migration/dirtyrate.c >>>>>>> +++ b/migration/dirtyrate.c >>>>>>> @@ -25,6 +25,7 @@ >>>>>>> #include "dirtyrate.h" >>>>>>> >>>>>>> CalculatingDirtyRateState CalculatingState = CAL_DIRTY_RATE_INIT; >>>>>>> +static unsigned long int qcrypto_hash_len = QCRYPTO_HASH_LEN; >>>>>> >>>>>> Why do we need this static rather than just using the QCRYPTO_HASH_LEN ? >>>>>> It's never going to change is it? >>>>>> (and anyway it's just a MD5 len?) >>>>> >>>>> I wouldn't want to bet on that given that this is use of MD5. We might >>>>> claim this isn't security critical, but surprises happen, and we will >>>>> certainly be dinged on security audits for introducing new use of MD5 >>>>> no matter what. >>>>> >>>>> If a cryptographic hash is required, then sha256 should be the choice >>>>> for any new code that doesn't have back compat requirements. >>>>> >>>>> If a cryptographic hash is not required then how about crc32 >>>> >>>> It doesn't need to be cryptographic; is crc32 the fastest reasonable hash for use >>>> in large areas? >>>> >>>> Dave >>>> >>>>> IOW, it doesn't make a whole lot of sense to say we need a cryptographic >>>>> hash, but then pick the most insecure one. >>>>> >>>>> sha256 is slower than md5, but it is conceivable that in future we might >>>>> gain support for something like Blake2b which is similar security level >>>>> to SHA3, while being faster than MD5. >>>>> >>>>> Overall I'm pretty unethusiastic about use of MD5 being introduced and >>>>> worse, being hardcoded as the only option. >>>>> >>>>> Regards, >>>>> Daniel >>>>> -- >>>>> |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| >>>>> |: https://libvirt.org -o- https://fstop138.berrange.com :| >>>>> |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| >>> >>> Hi, Daniel, Dave. >>> >>> I do compare MD5 and SHA256 with vm memory of 128G under mempress of 100G. >>> >>> 1. Calculation speed >>> 1） MD5 takes about 500ms to sample and hash all pages by record_ramblock_hash_info(). >>> 2) SHA256 takes about 750ms to sample all pages by record_ramblock_hash_info(). >>> >>> 2. CPU Consumption >>> 1) MD5 may have instant rise up to 48% for dirtyrate thread >>> 2) SHA256 may have instant rise up to 75% for dirtyrate thread >>> >>> 3. Memory Consumption >>> SHA256 may need twice memory than MD5 due to its HASH_LEN. >>> >>> I am trying to consider if crc32 is more faster and takes less memory and is more safer than MD5? >> >> No, crc32 is absolutely *weaker* than MD5. It is NOT a cryptographic >> hash so does not try to guarantee collision resistance. It only has >> 2^32 possible outputs. >> >> MD5 does try to guarantee collision resistance, but MD5 is considered >> broken these days, so a malicious attacker can cause collisions if they >> are motivated enough. >> >> IOW if you need collision resistance that SHA256 should be used. > > There's no need to guard against malicious behaviour here - this is just > a stat to guide migration. > If CRC32 is likely to be faster than md5 I suspect it's enough. > > Dave > OK, i'll take a test by crc32. >> >> Regards, >> Daniel >> -- >> |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| >> |: https://libvirt.org -o- https://fstop138.berrange.com :| >> |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|