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=-8.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 C1AF8C10DCE for ; Fri, 6 Mar 2020 16:57:21 +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 91802208C3 for ; Fri, 6 Mar 2020 16:57:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="C0ZGQb6s" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 91802208C3 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]:39120 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jAGHo-0007rJ-Mw for qemu-devel@archiver.kernel.org; Fri, 06 Mar 2020 11:57:20 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:33454) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jAGH3-0007Sa-UC for qemu-devel@nongnu.org; Fri, 06 Mar 2020 11:56:36 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1jAGH2-0007Bs-B9 for qemu-devel@nongnu.org; Fri, 06 Mar 2020 11:56:33 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:28176 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1jAGH2-00078X-5N for qemu-devel@nongnu.org; Fri, 06 Mar 2020 11:56:32 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1583513791; 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=t5yr1TzEBIlol8WEebzanSBrb5i2ZKuJ8aFfs9+94vU=; b=C0ZGQb6syptVoVbRqGuK766RBxfwJ7rqbvsyUetuia5q4wt1z8tkD2O4wOTf4kYd6ZwhyW qTJ3wx073gZQOyM4OvOSgrTl4L++H9Nn+0RQV2eZzl8vQ+OoGVWczAG5pjToLoBnkmnn4u qJuxmUYZlkZ6cXEdMy1kiEIWtNfxfIQ= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-388-V8ostj0eP4uLmOPjFf2XYA-1; Fri, 06 Mar 2020 11:56:29 -0500 X-MC-Unique: V8ostj0eP4uLmOPjFf2XYA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7A9DB184C80C; Fri, 6 Mar 2020 16:56:28 +0000 (UTC) Received: from work-vm (ovpn-116-247.ams2.redhat.com [10.36.116.247]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 145A45DA2C; Fri, 6 Mar 2020 16:56:18 +0000 (UTC) Date: Fri, 6 Mar 2020 16:56:15 +0000 From: "Dr. David Alan Gilbert" To: David Hildenbrand Subject: Re: [PATCH v3 10/13] migration/ram: Handle RAM block resizes during postcopy Message-ID: <20200306165615.GG3033@work-vm> References: <20200226155304.60219-1-david@redhat.com> <20200226155304.60219-11-david@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200226155304.60219-11-david@redhat.com> User-Agent: Mutt/1.13.3 (2020-01-12) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.120 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 , "Michael S. Tsirkin" , Richard Henderson , qemu-devel@nongnu.org, Peter Xu , Shannon Zhao , Igor Mammedov , Paolo Bonzini , Alex =?iso-8859-1?Q?Benn=E9e?= , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * David Hildenbrand (david@redhat.com) wrote: > Resizing while migrating is dangerous and does not work as expected. > The whole migration code works on the usable_length of ram blocks and doe= s > not expect this to change at random points in time. >=20 > In the case of postcopy, relying on used_length is racy as soon as the > guest is running. Also, when used_length changes we might leave the > uffd handler registered for some memory regions, reject valid pages > when migrating and fail when sending the recv bitmap to the source. >=20 > Resizing can be trigger *after* (but not during) a reset in > ACPI code by the guest > - hw/arm/virt-acpi-build.c:acpi_ram_update() > - hw/i386/acpi-build.c:acpi_ram_update() >=20 > Let's remember the original used_length in a separate variable and > use it in relevant postcopy code. Make sure to update it when we resize > during precopy, when synchronizing the RAM block sizes with the source. >=20 > Reviewed-by: Peter Xu > Cc: "Dr. David Alan Gilbert" > Cc: Juan Quintela > Cc: Eduardo Habkost > Cc: Paolo Bonzini > Cc: Igor Mammedov > Cc: "Michael S. Tsirkin" > Cc: Richard Henderson > Cc: Shannon Zhao > Cc: Alex Benn=E9e > Cc: Peter Xu > Signed-off-by: David Hildenbrand > --- > include/exec/ramblock.h | 10 ++++++++++ > migration/postcopy-ram.c | 15 ++++++++++++--- > migration/ram.c | 11 +++++++++-- > 3 files changed, 31 insertions(+), 5 deletions(-) >=20 > diff --git a/include/exec/ramblock.h b/include/exec/ramblock.h > index 07d50864d8..664701b759 100644 > --- a/include/exec/ramblock.h > +++ b/include/exec/ramblock.h > @@ -59,6 +59,16 @@ struct RAMBlock { > */ > unsigned long *clear_bmap; > uint8_t clear_bmap_shift; > + > + /* > + * RAM block length that corresponds to the used_length on the migra= tion > + * source (after RAM block sizes were synchronized). Especially, aft= er > + * starting to run the guest, used_length and postcopy_length can di= ffer. > + * Used to register/unregister uffd handlers and as the size of the = received > + * bitmap. Receiving any page beyond this length will bail out, as i= t > + * could not have been valid on the source. > + */ > + ram_addr_t postcopy_length; > }; > #endif > #endif > diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c > index a36402722b..c68caf4e42 100644 > --- a/migration/postcopy-ram.c > +++ b/migration/postcopy-ram.c > @@ -17,6 +17,7 @@ > */ > =20 > #include "qemu/osdep.h" > +#include "qemu/rcu.h" > #include "exec/target_page.h" > #include "migration.h" > #include "qemu-file.h" > @@ -31,6 +32,7 @@ > #include "qemu/error-report.h" > #include "trace.h" > #include "hw/boards.h" > +#include "exec/ramblock.h" > =20 > /* Arbitrary limit on size of each discard command, > * keeps them around ~200 bytes > @@ -456,6 +458,13 @@ static int init_range(RAMBlock *rb, void *opaque) > ram_addr_t length =3D qemu_ram_get_used_length(rb); > trace_postcopy_init_range(block_name, host_addr, offset, length); > =20 > + /* > + * Save the used_length before running the guest. In case we have to > + * resize RAM blocks when syncing RAM block sizes from the source du= ring > + * precopy, we'll update it manually via the ram block notifier. > + */ > + rb->postcopy_length =3D length; > + > /* > * We need the whole of RAM to be truly empty for postcopy, so thing= s > * like ROMs and any data tables built during init must be zero'd > @@ -478,7 +487,7 @@ static int cleanup_range(RAMBlock *rb, void *opaque) > const char *block_name =3D qemu_ram_get_idstr(rb); > void *host_addr =3D qemu_ram_get_host_addr(rb); > ram_addr_t offset =3D qemu_ram_get_offset(rb); > - ram_addr_t length =3D qemu_ram_get_used_length(rb); > + ram_addr_t length =3D rb->postcopy_length; > MigrationIncomingState *mis =3D opaque; > struct uffdio_range range_struct; > trace_postcopy_cleanup_range(block_name, host_addr, offset, length); > @@ -600,7 +609,7 @@ static int nhp_range(RAMBlock *rb, void *opaque) > const char *block_name =3D qemu_ram_get_idstr(rb); > void *host_addr =3D qemu_ram_get_host_addr(rb); > ram_addr_t offset =3D qemu_ram_get_offset(rb); > - ram_addr_t length =3D qemu_ram_get_used_length(rb); > + ram_addr_t length =3D rb->postcopy_length; > trace_postcopy_nhp_range(block_name, host_addr, offset, length); > =20 > /* > @@ -644,7 +653,7 @@ static int ram_block_enable_notify(RAMBlock *rb, void= *opaque) > struct uffdio_register reg_struct; > =20 > reg_struct.range.start =3D (uintptr_t)qemu_ram_get_host_addr(rb); > - reg_struct.range.len =3D qemu_ram_get_used_length(rb); > + reg_struct.range.len =3D rb->postcopy_length; > reg_struct.mode =3D UFFDIO_REGISTER_MODE_MISSING; > =20 > /* Now tell our userfault_fd that it's responsible for this area */ > diff --git a/migration/ram.c b/migration/ram.c > index 1a5ff07997..ee5c3d5784 100644 > --- a/migration/ram.c > +++ b/migration/ram.c > @@ -244,7 +244,7 @@ int64_t ramblock_recv_bitmap_send(QEMUFile *file, > return -1; > } > =20 > - nbits =3D block->used_length >> TARGET_PAGE_BITS; > + nbits =3D block->postcopy_length >> TARGET_PAGE_BITS; > =20 > /* > * Make sure the tmp bitmap buffer is big enough, e.g., on 32bit > @@ -3160,7 +3160,13 @@ static int ram_load_postcopy(QEMUFile *f) > break; > } > =20 > - if (!offset_in_ramblock(block, addr)) { > + /* > + * Relying on used_length is racy and can result in false po= sitives. > + * We might place pages beyond used_length in case RAM was s= hrunk > + * while in postcopy, which is fine - trying to place via > + * UFFDIO_COPY/UFFDIO_ZEROPAGE will never segfault. > + */ Is this actually safe? Imagine that the region had got shrunk, would it still be mmap'd in there - or could there now be a space where something else might have landed in? > + if (!block->host || addr >=3D block->postcopy_length) { > error_report("Illegal RAM offset " RAM_ADDR_FMT, addr); > ret =3D -EINVAL; > break; > @@ -3757,6 +3763,7 @@ static void ram_mig_ram_block_resized(RAMBlockNotif= ier *n, void *host, > rb->idstr); > } > } > + rb->postcopy_length =3D new_size; > break; > case POSTCOPY_INCOMING_NONE: > case POSTCOPY_INCOMING_RUNNING: > --=20 > 2.24.1 >=20 -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK