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=-15.2 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,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 B5D6DC4338F for ; Thu, 5 Aug 2021 07:50:39 +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 21BE960E52 for ; Thu, 5 Aug 2021 07:50:39 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 21BE960E52 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]:49148 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mBY9G-0006hx-AF for qemu-devel@archiver.kernel.org; Thu, 05 Aug 2021 03:50:38 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:54226) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mBY7Y-0004LW-7h for qemu-devel@nongnu.org; Thu, 05 Aug 2021 03:48:52 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:37210) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mBY7W-0002ag-L3 for qemu-devel@nongnu.org; Thu, 05 Aug 2021 03:48:52 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1628149730; 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=CcDBk7GZxgB8bFAKx8hY0L3+6fDnaDfWDM0bE8SjWGg=; b=MZ5n+klZuCcbp3/enLwUz8q6gDlZb7RHoZiBZEsT03qZMrda01YduUxE4t+oxJWpkW6/KJ rB7HGex/J/iOxx7MpitqZJIjkAr/n34nxbPF5VsHHqUqadgVBD2yxPx/oZA9BlNiU1T70+ 2Oeb4o8d0dZQ6j9UjrofargEDuMBKAA= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-501-moRneOInMAGiAj6iUg0N0Q-1; Thu, 05 Aug 2021 03:48:49 -0400 X-MC-Unique: moRneOInMAGiAj6iUg0N0Q-1 Received: by mail-wr1-f69.google.com with SMTP id p12-20020a5d68cc0000b02901426384855aso1624127wrw.11 for ; Thu, 05 Aug 2021 00:48:48 -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:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=CcDBk7GZxgB8bFAKx8hY0L3+6fDnaDfWDM0bE8SjWGg=; b=FsIG2gU/v2reBNQYAi6pZgVIw9pocRIXTDATtjnsitKBZjX8UcldLtkcwHl9jnTWUq kYyay3/6H6nobY3aEQHrB/jqnBGljyhUd+5KFnh9XMsEIDQsYn0suOzxlsgvcnrsRFtR /ob9+XU91yqkE+Ih9NIk27M46bVnJTBfAu8pQY/swtzAFclMdfL+jiGXd4UDgmSckJOS 3bn2O47KGEE3+X/yE6K628aFjZtz+V/d8j5/ZRHNe7DfjSJI29Lchym5YS1qUELZY3Z7 03id6K5lTNuQeoe6tOoknOlY6XH+VJQvf9DP8kpH9Ech1Em0rWN2jcGUkhQ/mXxKUUmT iLdg== X-Gm-Message-State: AOAM530Pb+zZZ4IarbgeJ6+a8zwIrSxmoMgVK1Mayv628BuCcWyHDW4w dt7uYn53ZmiZbPtLeMN2Lp7RfuEKM8z48W7+NG311aoXUJ6lq2tFn1fk7TIWbVbc6A2H2xLgUo0 eypmALtT6+weuyEE= X-Received: by 2002:a1c:1b17:: with SMTP id b23mr13584129wmb.178.1628149727878; Thu, 05 Aug 2021 00:48:47 -0700 (PDT) X-Google-Smtp-Source: ABdhPJx28coKpYTwrLEmC0d46C9+/FuRd1DckBUG+ocWI+n3blVtw7Q1zSwhrc0P/37GZuqR6jWfVw== X-Received: by 2002:a1c:1b17:: with SMTP id b23mr13584112wmb.178.1628149727729; Thu, 05 Aug 2021 00:48:47 -0700 (PDT) Received: from [192.168.43.238] (166.red-193-152-126.dynamicip.rima-tde.net. [193.152.126.166]) by smtp.gmail.com with ESMTPSA id n30sm6025601wra.1.2021.08.05.00.48.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Aug 2021 00:48:47 -0700 (PDT) Subject: Re: [PATCH v3 6/7] migration/postcopy: Handle RAMBlocks with a RamDiscardManager on the destination To: David Hildenbrand , qemu-devel@nongnu.org References: <20210730085249.8246-1-david@redhat.com> <20210730085249.8246-7-david@redhat.com> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: <5f8c6173-046d-9fc2-c649-93ede45ca77d@redhat.com> Date: Thu, 5 Aug 2021 09:48:45 +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: <20210730085249.8246-7-david@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=philmd@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=philmd@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=-0.699, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.132, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=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: Alex Williamson , Eduardo Habkost , Juan Quintela , "Michael S. Tsirkin" , "Dr. David Alan Gilbert" , Peter Xu , Andrey Gruzdev , Pankaj Gupta , teawater , Paolo Bonzini , Marek Kedzierski , Wei Yang Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 7/30/21 10:52 AM, David Hildenbrand wrote: > Currently, when someone (i.e., the VM) accesses discarded parts inside a > RAMBlock with a RamDiscardManager managing the corresponding mapped memory > region, postcopy will request migration of the corresponding page from the > source. The source, however, will never answer, because it refuses to > migrate such pages with undefined content ("logically unplugged"): the > pages are never dirty, and get_queued_page() will consequently skip > processing these postcopy requests. > > Especially reading discarded ("logically unplugged") ranges is supposed to > work in some setups (for example with current virtio-mem), although it > barely ever happens: still, not placing a page would currently stall the > VM, as it cannot make forward progress. > > Let's check the state via the RamDiscardManager (the state e.g., > of virtio-mem is migrated during precopy) and avoid sending a request > that will never get answered. Place a fresh zero page instead to keep > the VM working. This is the same behavior that would happen > automatically without userfaultfd being active, when accessing virtual > memory regions without populated pages -- "populate on demand". > > For now, there are valid cases (as documented in the virtio-mem spec) where > a VM might read discarded memory; in the future, we will disallow that. > Then, we might want to handle that case differently, e.g., warning the > user that the VM seems to be mis-behaving. > > Signed-off-by: David Hildenbrand > --- > migration/postcopy-ram.c | 31 +++++++++++++++++++++++++++---- > migration/ram.c | 21 +++++++++++++++++++++ > migration/ram.h | 1 + > 3 files changed, 49 insertions(+), 4 deletions(-) > > diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c > index 2e9697bdd2..38cdfc09c3 100644 > --- a/migration/postcopy-ram.c > +++ b/migration/postcopy-ram.c > @@ -671,6 +671,29 @@ int postcopy_wake_shared(struct PostCopyFD *pcfd, > return ret; > } > > +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)); void *aligned = QEMU_ALIGN_PTR_DOWN(haddr, qemu_ram_pagesize(rb)));