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=-5.3 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 A268CC4361B for ; Mon, 14 Dec 2020 02:15:47 +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 E51D92376F for ; Mon, 14 Dec 2020 02:15:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E51D92376F 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]:52624 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kodOr-0007Ra-Ij for qemu-devel@archiver.kernel.org; Sun, 13 Dec 2020 21:15:45 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:48506) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kodNh-0006hN-CU for qemu-devel@nongnu.org; Sun, 13 Dec 2020 21:14:33 -0500 Received: from szxga07-in.huawei.com ([45.249.212.35]:2169) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kodNf-0003qq-5g for qemu-devel@nongnu.org; Sun, 13 Dec 2020 21:14:33 -0500 Received: from DGGEMS407-HUB.china.huawei.com (unknown [172.30.72.60]) by szxga07-in.huawei.com (SkyGuard) with ESMTP id 4CvQ123Mphz7FG2; Mon, 14 Dec 2020 10:13:42 +0800 (CST) Received: from [10.174.187.37] (10.174.187.37) by DGGEMS407-HUB.china.huawei.com (10.3.19.207) with Microsoft SMTP Server id 14.3.498.0; Mon, 14 Dec 2020 10:14:11 +0800 Subject: Re: [PATCH] kvm: Take into account the unaligned section size when preparing bitmap To: Peter Xu References: <20201208114013.875-1-yuzenghui@huawei.com> <20201208151654.GA6432@xz-x1> <6dc82702-9246-4684-4f28-e104abc0c11d@huawei.com> <20201210020843.GB3211@xz-x1> <7d46e5ca-24ab-7c44-201c-77e8fc6a2ace@huawei.com> <20201210145006.GD3211@xz-x1> <2607b4cd-524c-2360-6261-224736861fc4@huawei.com> <20201211152518.GD6520@xz-x1> From: zhukeqian Message-ID: <41d9ac96-83af-e8c3-6e54-c702f5527f5e@huawei.com> Date: Mon, 14 Dec 2020 10:14:11 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1 MIME-Version: 1.0 In-Reply-To: <20201211152518.GD6520@xz-x1> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.187.37] X-CFilter-Loop: Reflected Received-SPF: pass client-ip=45.249.212.35; envelope-from=zhukeqian1@huawei.com; helo=szxga07-in.huawei.com 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, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_MSPIKE_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-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: Zenghui Yu , pbonzini@redhat.com, qemu-devel@nongnu.org, wanghaibin.wang@huawei.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2020/12/11 23:25, Peter Xu wrote: > On Fri, Dec 11, 2020 at 09:13:10AM +0800, zhukeqian wrote: >> >> On 2020/12/10 22:50, Peter Xu wrote: >>> On Thu, Dec 10, 2020 at 10:53:23AM +0800, zhukeqian wrote: >>>> >>>> >>>> On 2020/12/10 10:08, Peter Xu wrote: >>>>> Keqian, >>>>> >>>>> On Thu, Dec 10, 2020 at 09:46:06AM +0800, zhukeqian wrote: >>>>>> Hi, >>>>>> >>>>>> I see that if start or size is not PAGE aligned, it also clears areas >>>>>> which beyond caller's expectation, so do we also need to consider this? >>>>> >>>>> Could you elaborate? >>>>> >>>>> If start_delta != 0, kvm_log_clear_one_slot() should already go the slow path. >>>>> >>>>> Thanks, >>>>> >>>> >>>> Hi Peter, >>>> >>>> start_delta /= psize; >>>> >>>> If start is not PAGE aligned, then start_delta is not PAGE aligned. >>>> so I think the above code will implicitly extend our start to be PAGE aligned. >>>> >>>> I suggest that we should shrink the start and (start + size) to be PAGE aligned >>>> at beginning of this function. >>> >>> Callers should be with TARGET_PAGE_SIZE aligned on the size, so at least x86_64 >>> should be pretty safe since host/guest page sizes match. >>> >>> Though indeed I must confess I don't know how it worked in general when host >>> page size != target page size, at least for migration. For example, I believe >>> kvm dirty logging is host page size based, though migration should be migrating >>> pages in guest page size granule when it spots a dirty bit set. >>> >> Hi, >> >> Indeed, we handle target_page_size aligned @start and @size in general. Maybe we'd better >> add explicit function comments about alignment requirement, and explicit alignment assert >> on @start and @size? > Hi Peter, > Yes we can, but I think it's not strongly necessary. As Zenghui pointed out, > the callers of memory_region_clear_dirty_bitmap() should always be aware of the > fact that dirty bitmap is always page size based. Agree. > > OTOH I'm more worried on the other question on how we handle guest psize != > host psize case for migration now... I think it does not matter when guest_psize != host_psize, as we only need to interact with stage2 page tables during migration. Stage2 is enough to tracking guest dirty memory, and even if guest close stage1, we also can do a successful migration. Please point out if I misunderstood what you meant. Thanks, Keqian > > Thanks, >