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=-5.2 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 529EBC4338F for ; Thu, 29 Jul 2021 19:24:57 +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 E34FF60560 for ; Thu, 29 Jul 2021 19:24:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org E34FF60560 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:36980 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1m9BeJ-0004ts-PM for qemu-devel@archiver.kernel.org; Thu, 29 Jul 2021 15:24:55 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42096) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1m9BcJ-000391-DC for qemu-devel@nongnu.org; Thu, 29 Jul 2021 15:22:51 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:43811) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1m9BcH-0007nD-Nk for qemu-devel@nongnu.org; Thu, 29 Jul 2021 15:22:51 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1627586569; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=/W6V/QwFbfmSoI18mcFu5r7Qthog7nUKOqiwQjODHm4=; b=ExhQ3sWissWzYS8ZUs6bs09TE0lK52nN9em+h5/2SoNphP0LB78WqQiRSSMHELVBvgfFOa zK8M6N3lLBmkUUznsoLniOoedcfX+MlcvzFq5TtmeWAbqIiTdrvSJj7yZS1sLMKUAoOQWZ FUJ+KvDzXUEBSmX9C4EpjXutUmiy1qg= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-396-Zj3_nk-RMrmKBklU8QnhhA-1; Thu, 29 Jul 2021 15:22:47 -0400 X-MC-Unique: Zj3_nk-RMrmKBklU8QnhhA-1 Received: by mail-wm1-f70.google.com with SMTP id u14-20020a7bcb0e0000b0290248831d46e4so2312867wmj.6 for ; Thu, 29 Jul 2021 12:22:47 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:organization :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=/W6V/QwFbfmSoI18mcFu5r7Qthog7nUKOqiwQjODHm4=; b=s9ax8omWlvv8EP1aU8CEW9hp0gyBumsBPHIJhriQoVflg1SfAFzlqVdb7S2fGYvy5+ 0WAF5pG0gQ+V/uUYlwpzBhBKzJ3ebJhCx0S2txkTJpKh8dkS7tEnA42o3OWsXxVYsHQJ HXlfYNw6sDxxRlw+6GFxHwDekYFsXG/nPLW5fydyuZQKY5kGJG9Xp+gfTi4+pn78yS7Z OvEaD4N1J8Oe7fUWzy3ltQmbVOcC9YKU4+zgkUN9anvCyev+NaPfWXZPfTOVWQcFZXlW SH977/6ydWWJAOHMa4nyjBVOjGrarqSm9T3bl09ZfJYi5aYlg+e7jzHCYdKgvzZUhsz3 pviA== X-Gm-Message-State: AOAM531/79Qas62XN+csJFd9nHoHpe7qU7lwYVchWmHdgSPSKjjQSFqa GxL6I/g84fpJ5C5R8/EFp7Ko1TYTqSq4axGsanH0ImKYWMC5AkdJ7jpwmQSbOaMYWVMd/WR2rTR SaHDNcfrdIU91inU= X-Received: by 2002:adf:f351:: with SMTP id e17mr6614163wrp.360.1627586566669; Thu, 29 Jul 2021 12:22:46 -0700 (PDT) X-Google-Smtp-Source: ABdhPJweGU10mga25+BOncguqQncreCN0U6xFodeRvuZJ0PK+34zKrBO0edNecWpvgXTsq0prXSLBA== X-Received: by 2002:adf:f351:: with SMTP id e17mr6614138wrp.360.1627586566451; Thu, 29 Jul 2021 12:22:46 -0700 (PDT) Received: from ?IPv6:2003:d8:2f0a:7f00:fad7:3bc9:69d:31f? (p200300d82f0a7f00fad73bc9069d031f.dip0.t-ipconnect.de. [2003:d8:2f0a:7f00:fad7:3bc9:69d:31f]) by smtp.gmail.com with ESMTPSA id j140sm4269135wmj.37.2021.07.29.12.22.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 29 Jul 2021 12:22:45 -0700 (PDT) Subject: Re: [PATCH v2 5/6] migration/postcopy: Handle RAMBlocks with a RamDiscardManager on the destination To: Peter Xu References: <20210721092759.21368-1-david@redhat.com> <20210721092759.21368-6-david@redhat.com> <2ce949f2-6950-5404-70e4-73a2e41b4ca8@redhat.com> <124693ef-5595-85c9-da5a-8f8e6a827c19@redhat.com> <5ede7b00-1048-c124-e239-eeff21d9adb0@redhat.com> From: David Hildenbrand Organization: Red Hat Message-ID: Date: Thu, 29 Jul 2021 21:22:44 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=david@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.717, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.125, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, 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: Eduardo Habkost , Juan Quintela , Pankaj Gupta , "Michael S. Tsirkin" , teawater , qemu-devel@nongnu.org, "Dr. David Alan Gilbert" , Alex Williamson , Marek Kedzierski , Paolo Bonzini , Andrey Gruzdev , Wei Yang Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 29.07.21 21:20, Peter Xu wrote: > On Thu, Jul 29, 2021 at 06:15:58PM +0200, David Hildenbrand wrote: >> On 29.07.21 17:52, Peter Xu wrote: >>> On Thu, Jul 29, 2021 at 02:14:41PM +0200, David Hildenbrand wrote: >>>> On 24.07.21 00:10, Peter Xu wrote: >>>>> On Fri, Jul 23, 2021 at 09:01:42PM +0200, David Hildenbrand wrote: >>>>>> It can happen in corner cases and is valid: with the current virtio-mem >>>>>> spec, guests are allowed to read unplugged memory. This will, for example, >>>>>> happen on older Linux guests when reading /proc/kcore or (with even older >>>>>> guests) when dumping guest memory via kdump. These corner cases were the >>>>>> main reason why the spec allows for it -- until we have guests properly >>>>>> adjusted such that it won't happen even in corner cases. >>>>>> >>>>>> A future feature bit will disallow it for the guest: required for supporting >>>>>> shmem/hugetlb cleanly. With that in place, I agree that we would want to >>>>>> warn in this case! >>>>> >>>>> OK that makes sense; with the page_size change, feel free to add: >>>> >>>> I just realized that relying on the page_size would be wrong. >>>> >>>> We migrate TARGET_PAGE_SIZE chunks and the offset might not be page_size >>>> aligned. So if we were to replace TARGET_PAGE_SIZE by rb->page_size, we >>>> might accidentally cover a "too big" range. >>> >>> I'm wondering whether we should make the offset page size aligned instead. For >>> example, note that postcopy_place_page_zero() should only take page_size >>> aligned host addr or UFFDIO_COPY could fail (hugetlb doesn't support >>> UFFDIO_ZEROPAGE yet). >> >> That is true indeed. I'd assume in that case that we would get called with >> the proper offset already, right? Because uffd would only report properly >> aligned pages IIRC. > > Nop; it should return the faulted address. So postcopy_request_page() may need > some alignment work, as it was handled in migrate_send_rp_req_pages(). > Right, figured that out myself just now: static int postcopy_request_page(MigrationIncomingState *mis, RAMBlock *rb, ram_addr_t start, uint64_t haddr) { void *aligned = (void *)(uintptr_t)(haddr & -qemu_ram_pagesize(rb)); /* * Discarded pages (via RamDiscardManager) are never migrated. On unlikely * access, place a zeropage, which will also set the relevant bits in the * recv_bitmap accordingly, so we won't try placing a zeropage twice. * * Checking a single bit is sufficient to handle pagesize > TPS as either * all relevant bits are set or not. */ assert(QEMU_IS_ALIGNED(start, qemu_ram_pagesize(rb))); if (ramblock_page_is_discarded(rb, start)) { bool received = ramblock_recv_bitmap_test_byte_offset(rb, start); return received ? 0 : postcopy_place_page_zero(mis, aligned, rb); } return migrate_send_rp_req_pages(mis, rb, start, haddr); } -- Thanks, David / dhildenb