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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 6247CC76192 for ; Wed, 17 Jul 2019 11:07:11 +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 3B3332173B for ; Wed, 17 Jul 2019 11:07:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3B3332173B 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]:55970 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hnhmA-0000F3-B4 for qemu-devel@archiver.kernel.org; Wed, 17 Jul 2019 07:07:10 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:37777) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hnhlu-0007rU-1d for qemu-devel@nongnu.org; Wed, 17 Jul 2019 07:06:55 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hnhls-0006gB-OA for qemu-devel@nongnu.org; Wed, 17 Jul 2019 07:06:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44138) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hnhls-0006ek-Fi; Wed, 17 Jul 2019 07:06:52 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id B1634C055673; Wed, 17 Jul 2019 11:06:51 +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 ED6D1600D1; Wed, 17 Jul 2019 11:06:42 +0000 (UTC) Date: Wed, 17 Jul 2019 07:06:40 -0400 From: "Michael S. Tsirkin" To: David Hildenbrand Message-ID: <20190717070323-mutt-send-email-mst@kernel.org> References: <20190717084255.17173-1-david@redhat.com> <20190717054727-mutt-send-email-mst@kernel.org> <5a5d6f86-04f2-4e61-473c-d8a4b0ed5045@redhat.com> <5d50ddb0-b1ac-0bd1-6466-6e605b804809@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5d50ddb0-b1ac-0bd1-6466-6e605b804809@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Wed, 17 Jul 2019 11:06:51 +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] virtio-balloon: fix QEMU crashes on pagesize > BALLOON_PAGE_SIZE 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 , David Gibson , qemu-devel@nongnu.org, Stefan Hajnoczi , qemu-stable@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jul 17, 2019 at 12:17:57PM +0200, David Hildenbrand wrote: > On 17.07.19 12:04, David Hildenbrand wrote: > > On 17.07.19 11:57, Michael S. Tsirkin wrote: > >> On Wed, Jul 17, 2019 at 10:42:55AM +0200, David Hildenbrand wrote: > >>> We are using the wrong functions to set/clear bits, effectively touching > >>> multiple bits, writing out of range of the bitmap, resulting in memory > >>> corruptions. We have to use set_bit()/clear_bit() instead. > >>> > >>> Can easily be reproduced by starting a qemu guest on hugetlbfs memory, > >>> inflating the balloon. QEMU crashes. This never could have worked > >>> properly - especially, also pages would have been discarded when the > >>> first sub-page would be inflated (the whole bitmap would be set). > >>> > >>> While testing I realized, that on hugetlbfs it is pretty much impossible > >>> to discard a page - the guest just frees the 4k sub-pages in random order > >>> most of the time. I was only able to discard a hugepage a handful of > >>> times - so I hope that now works correctly. > >>> > >>> Fixes: ed48c59875b6 ("virtio-balloon: Safely handle BALLOON_PAGE_SIZE < > >>> host page size") > >>> Fixes: b27b32391404 ("virtio-balloon: Fix possible guest memory corruption > >>> with inflates & deflates") > >>> 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 > >>> --- > >>> hw/virtio/virtio-balloon.c | 10 ++++------ > >>> 1 file changed, 4 insertions(+), 6 deletions(-) > >>> > >>> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c > >>> index e85d1c0d5c..669067d661 100644 > >>> --- a/hw/virtio/virtio-balloon.c > >>> +++ b/hw/virtio/virtio-balloon.c > >>> @@ -94,9 +94,8 @@ static void balloon_inflate_page(VirtIOBalloon *balloon, > >>> balloon->pbp->base = host_page_base; > >>> } > >>> > >>> - bitmap_set(balloon->pbp->bitmap, > >>> - (ram_offset - balloon->pbp->base) / BALLOON_PAGE_SIZE, > >>> - subpages); > >>> + set_bit((ram_offset - balloon->pbp->base) / BALLOON_PAGE_SIZE, > >>> + balloon->pbp->bitmap); > >>> > >>> if (bitmap_full(balloon->pbp->bitmap, subpages)) { > >>> /* We've accumulated a full host page, we can actually discard > >>> @@ -140,9 +139,8 @@ static void balloon_deflate_page(VirtIOBalloon *balloon, > >>> * for a guest to do this in practice, but handle it anyway, > >>> * since getting it wrong could mean discarding memory the > >>> * guest is still using. */ > >>> - bitmap_clear(balloon->pbp->bitmap, > >>> - (ram_offset - balloon->pbp->base) / BALLOON_PAGE_SIZE, > >>> - subpages); > >>> + clear_bit((ram_offset - balloon->pbp->base) / BALLOON_PAGE_SIZE, > >>> + balloon->pbp->bitmap); > >>> > >>> if (bitmap_empty(balloon->pbp->bitmap, subpages)) { > >>> g_free(balloon->pbp); > >> > >> I also started to wonder about this: > >> > >> if (!balloon->pbp) { > >> /* Starting on a new host page */ > >> size_t bitlen = BITS_TO_LONGS(subpages) * sizeof(unsigned long); > >> balloon->pbp = g_malloc0(sizeof(PartiallyBalloonedPage) + bitlen); > >> balloon->pbp->rb = rb; > >> balloon->pbp->base = host_page_base; > >> } > >> > >> Is keeping a pointer to a ram block like this safe? what if the ramblock > >> gets removed? > >> > > > > David added > > > > if (balloon->pbp > > && (rb != balloon->pbp->rb ) ... > > > > So in case the rb changes (IOW replaced - delete old one, new one > > added), we reset the data. > > > > After a ram block was deleted, there will be no more deflation requests > > coming in for it. This should be fine I guess. I think it might happen that an old dangling pointer happens to match a newly allocated one. I think we really should just cache all data we want to take into account and compare that. > > > > > > However, there is another possible issue: Resets. > > > > If the balloon was inflated and we reboot, the old balloon->pbp will > > remain intact. The guest will continue using all memory until > > virtio-balloon guest driver comes up. If the stars align, it could > > happen that new inflation requests by the guests will result in a > > discard of a big chunk, although the guest is re-using some parts > > already again. > > > > We would have to reset balloon->pbp during virtio_balloon_device_reset(). > > > > ... also, I think balloon->pbp is not freed when unrealizing, resulting > in a memory leak ... > > will craft some more patches. Ught. > -- > > Thanks, > > David / dhildenb