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=-3.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 D05A5C76186 for ; Wed, 17 Jul 2019 11:29:42 +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 A164520880 for ; Wed, 17 Jul 2019 11:29:42 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A164520880 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:56122 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hni7x-0002qy-Ue for qemu-devel@archiver.kernel.org; Wed, 17 Jul 2019 07:29:41 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:44479) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hni7n-0002SF-AZ for qemu-devel@nongnu.org; Wed, 17 Jul 2019 07:29:32 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hni7m-0006Io-6e for qemu-devel@nongnu.org; Wed, 17 Jul 2019 07:29:31 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39868) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hni7k-0006Hn-KI; Wed, 17 Jul 2019 07:29:29 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 92C62308A9BE; Wed, 17 Jul 2019 11:29:27 +0000 (UTC) Received: from redhat.com (ovpn-120-247.rdu2.redhat.com [10.10.120.247]) by smtp.corp.redhat.com (Postfix) with SMTP id 2E33B608A6; Wed, 17 Jul 2019 11:29:20 +0000 (UTC) Date: Wed, 17 Jul 2019 07:29:19 -0400 From: "Michael S. Tsirkin" To: David Hildenbrand Message-ID: <20190717072551-mutt-send-email-mst@kernel.org> References: <20190717103550.24657-1-david@redhat.com> <20190717103550.24657-4-david@redhat.com> <20190717063902-mutt-send-email-mst@kernel.org> <0828606b-4cdf-63ea-9211-dc5905b00f4b@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0828606b-4cdf-63ea-9211-dc5905b00f4b@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Wed, 17 Jul 2019 11:29:27 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH-for-4.1 v2 3/3] virtio-balloon: reset pbp on device resets 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: Igor Mammedov , qemu-stable@nongnu.org, qemu-devel@nongnu.org, Stefan Hajnoczi , David Gibson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jul 17, 2019 at 01:06:29PM +0200, David Hildenbrand wrote: > On 17.07.19 12:48, Michael S. Tsirkin wrote: > > On Wed, Jul 17, 2019 at 12:35:50PM +0200, David Hildenbrand wrote: > >> When a guest reboots (ordinary reboots, but also via kexec), it will > >> happily reuse any system memory, including previously inflated memory. > >> > >> We could have tracking data for a pbp (PartiallyBalloonedPage). It could > >> happen that a new inflation request from the guest will result in a > >> discard of such a pbp, although the guest is (again) reusing some > >> memory. > >> > >> We should reset the pbp on any device resets. > >> > >> Fixes: ed48c59875b6 ("virtio-balloon: Safely handle BALLOON_PAGE_SIZE < > >> host page size") > >> Cc: qemu-stable@nongnu.org #v4.0.0 > >> Cc: Stefan Hajnoczi > >> Cc: David Gibson > >> Cc: Michael S. Tsirkin > >> Cc: Igor Mammedov > >> Signed-off-by: David Hildenbrand > > > > Can't something else remove a ramblock besides a reset? > > Yes, however this patch is not about ramblocks getting removed. > > Take a close look, "balloon->pbp->rb" is only used as a token, it is > never used besides for comparisons. You are right but that's still not safe :) E.g. the bit we are going to set could be out of range of the bitmap because the backing page size changed. > -- > > Thanks, > > David / dhildenb