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=-7.1 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,URG_BIZ,URIBL_BLOCKED,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 B14DAC35646 for ; Fri, 21 Feb 2020 15:41:21 +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 6A72F206E2 for ; Fri, 21 Feb 2020 15:41:21 +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="RQCf/W56" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6A72F206E2 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]:59994 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j5AQa-0002Ud-LK for qemu-devel@archiver.kernel.org; Fri, 21 Feb 2020 10:41:20 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:38931) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j5APq-0001zW-R1 for qemu-devel@nongnu.org; Fri, 21 Feb 2020 10:40:36 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1j5APp-0007iy-2y for qemu-devel@nongnu.org; Fri, 21 Feb 2020 10:40:34 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:52153 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 1j5APo-0007iB-TI for qemu-devel@nongnu.org; Fri, 21 Feb 2020 10:40:33 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1582299632; 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=w6sr7yRZF7qq5UE75Jg+44q1+YXuHEB0zJNbkxL3gTM=; b=RQCf/W56GPIKFj7PTlewHzDknqCn3sjzet3ebAdUer0zIscV/QqofxTPXy7WblXrUbBSAr YdF3Ziz94AWQXwwjQNXN4+hDp5z766z3vB6BfUcz/kbn9ijl78hrLcQNMxpdoBVJU8zgVL SdHnC/cNI5kon0o/Ts9cfM3AJpjFe6Y= 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-310-kfGQlPNOObWslniWl93S4Q-1; Fri, 21 Feb 2020 10:40:30 -0500 X-MC-Unique: kfGQlPNOObWslniWl93S4Q-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A7BF4800D53; Fri, 21 Feb 2020 15:40:29 +0000 (UTC) Received: from work-vm (unknown [10.36.118.1]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 040F31001B07; Fri, 21 Feb 2020 15:40:19 +0000 (UTC) Date: Fri, 21 Feb 2020 15:40:17 +0000 From: "Dr. David Alan Gilbert" To: David Hildenbrand Subject: Re: [PATCH v1 05/13] migrate/ram: Handle RAM block resizes during precopy Message-ID: <20200221154017.GG2931@work-vm> References: <20200219161725.115218-1-david@redhat.com> <20200219161725.115218-6-david@redhat.com> <20200221151447.GF2931@work-vm> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.13.3 (2020-01-12) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 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: > On 21.02.20 16:14, Dr. David Alan Gilbert wrote: > > * 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 = does > >> not expect this to change at random points in time. > >> > >> In the case of precopy, the ram block size must not change on the sour= ce, > >> after syncing the RAM block list in ram_save_setup(), so as long as th= e > >> guest is still running on the source. > >> > >> 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() > >> > >> Use the ram block notifier to get notified about resizes. Let's simply > >> cancel migration and indicate the reason. We'll continue running on th= e > >> source. No harm done. > >> > >> Update the documentation. Postcopy will be handled separately. > >> > >> 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 > >> --- > >> exec.c | 5 +++-- > >> include/exec/memory.h | 10 ++++++---- > >> migration/migration.c | 9 +++++++-- > >> migration/migration.h | 1 + > >> migration/ram.c | 41 +++++++++++++++++++++++++++++++++++++++++ > >> 5 files changed, 58 insertions(+), 8 deletions(-) > >> > >> diff --git a/exec.c b/exec.c > >> index b75250e773..8b015821d6 100644 > >> --- a/exec.c > >> +++ b/exec.c > >> @@ -2120,8 +2120,9 @@ static int memory_try_enable_merging(void *addr,= size_t len) > >> return qemu_madvise(addr, len, QEMU_MADV_MERGEABLE); > >> } > >> =20 > >> -/* Only legal before guest might have detected the memory size: e.g. = on > >> - * incoming migration, or right after reset. > >> +/* > >> + * Resizing RAM while migrating can result in the migration being can= celed. > >> + * Care has to be taken if the guest might have already detected the = memory. > >> * > >> * As memory core doesn't know how is memory accessed, it is up to > >> * resize callback to update device state and/or add assertions to de= tect > >> diff --git a/include/exec/memory.h b/include/exec/memory.h > >> index e85b7de99a..de111347e8 100644 > >> --- a/include/exec/memory.h > >> +++ b/include/exec/memory.h > >> @@ -113,7 +113,7 @@ typedef struct IOMMUNotifier IOMMUNotifier; > >> #define RAM_SHARED (1 << 1) > >> =20 > >> /* Only a portion of RAM (used_length) is actually used, and migrated= . > >> - * This used_length size can change across reboots. > >> + * Resizing RAM while migrating can result in the migration being can= celed. > >> */ > >> #define RAM_RESIZEABLE (1 << 2) > >> =20 > >> @@ -843,7 +843,9 @@ void memory_region_init_ram_shared_nomigrate(Memor= yRegion *mr, > >> * RAM. Accesses into the region= will > >> * modify memory directly. Only = an initial > >> * portion of this RAM is actuall= y used. > >> - * The used size can change acros= s reboots. > >> + * Changing the size while migrat= ing > >> + * can result in the migration be= ing > >> + * canceled. > >> * > >> * @mr: the #MemoryRegion to be initialized. > >> * @owner: the object that tracks the region's reference count > >> @@ -1464,8 +1466,8 @@ void *memory_region_get_ram_ptr(MemoryRegion *mr= ); > >> =20 > >> /* memory_region_ram_resize: Resize a RAM region. > >> * > >> - * Only legal before guest might have detected the memory size: e.g. = on > >> - * incoming migration, or right after reset. > >> + * Resizing RAM while migrating can result in the migration being can= celed. > >> + * Care has to be taken if the guest might have already detected the = memory. > >> * > >> * @mr: a memory region created with @memory_region_init_resizeable_r= am. > >> * @newsize: the new size the region > >> diff --git a/migration/migration.c b/migration/migration.c > >> index 8fb68795dc..ac9751dbe5 100644 > >> --- a/migration/migration.c > >> +++ b/migration/migration.c > >> @@ -175,13 +175,18 @@ void migration_object_init(void) > >> } > >> } > >> =20 > >> +void migration_cancel(void) > >> +{ > >> + migrate_fd_cancel(current_migration); > >> +} > >> + > >> void migration_shutdown(void) > >> { > >> /* > >> * Cancel the current migration - that will (eventually) > >> * stop the migration using this structure > >> */ > >> - migrate_fd_cancel(current_migration); > >> + migration_cancel(); > >> object_unref(OBJECT(current_migration)); > >> } > >> =20 > >> @@ -2019,7 +2024,7 @@ void qmp_migrate(const char *uri, bool has_blk, = bool blk, > >> =20 > >> void qmp_migrate_cancel(Error **errp) > >> { > >> - migrate_fd_cancel(migrate_get_current()); > >> + migration_cancel(); > >> } > >> =20 > >> void qmp_migrate_continue(MigrationStatus state, Error **errp) > >> diff --git a/migration/migration.h b/migration/migration.h > >> index 8473ddfc88..79fd74afa5 100644 > >> --- a/migration/migration.h > >> +++ b/migration/migration.h > >> @@ -343,5 +343,6 @@ int foreach_not_ignored_block(RAMBlockIterFunc fun= c, void *opaque); > >> void migration_make_urgent_request(void); > >> void migration_consume_urgent_request(void); > >> bool migration_rate_limit(void); > >> +void migration_cancel(void); > >> =20 > >> #endif > >> diff --git a/migration/ram.c b/migration/ram.c > >> index ed23ed1c7c..57f32011a3 100644 > >> --- a/migration/ram.c > >> +++ b/migration/ram.c > >> @@ -52,6 +52,7 @@ > >> #include "migration/colo.h" > >> #include "block.h" > >> #include "sysemu/sysemu.h" > >> +#include "sysemu/runstate.h" > >> #include "savevm.h" > >> #include "qemu/iov.h" > >> #include "multifd.h" > >> @@ -3710,8 +3711,48 @@ static SaveVMHandlers savevm_ram_handlers =3D { > >> .resume_prepare =3D ram_resume_prepare, > >> }; > >> =20 > >> +static void ram_mig_ram_block_resized(RAMBlockNotifier *n, void *host= , > >> + size_t old_size, size_t new_siz= e) > >> +{ > >> + ram_addr_t offset; > >> + Error *err =3D NULL; > >> + RAMBlock *rb =3D qemu_ram_block_from_host(host, false, &offset); > >> + > >> + if (ramblock_is_ignored(rb)) { > >> + return; > >> + } > >> + > >> + /* > >> + * Some resizes are triggered on the migration target by precopy = code, > >> + * when synchronizing RAM block sizes. In these cases, the VM is = not > >> + * running and migration is not idle. We have to ignore these res= izes, > >> + * as we only care about resizes during precopy on the migration = source. > >> + * This handler is always registered, so ignore when migration is= idle. > >> + */ > >> + if (migration_is_idle() || !runstate_is_running() || > >> + postcopy_is_running()) { > >> + return; > >> + } > >> + > >> + /* > >> + * Precopy code cannot deal with the size of ram blocks changing = at > >> + * random points in time. We're still running on the source, abor= t > >> + * the migration and continue running here. Make sure to wait unt= il > >> + * migration was canceled. > >> + */ > >> + error_setg(&err, "RAM block '%s' resized during precopy.", rb->id= str); > >> + migrate_set_error(migrate_get_current(), err); > >> + error_free(err); > >> + migration_cancel(); > >> +} > >> + > >> +static RAMBlockNotifier ram_mig_ram_notifier =3D { > >> + .ram_block_resized =3D ram_mig_ram_block_resized, > >> +}; > >> + > >> void ram_mig_init(void) > >> { > >> qemu_mutex_init(&XBZRLE.lock); > >> register_savevm_live("ram", 0, 4, &savevm_ram_handlers, &ram_stat= e); > >> + ram_block_notifier_add(&ram_mig_ram_notifier); > >=20 > > Can we avoid the question of the 'is_idle' checks by doing this > > registration in save_setup/load_setup and unregistering in > > save_cleanup/load_cleanup? >=20 > Well, I figured it out now :) >=20 > migration_is_idle() is enough to handle it in this patch. >=20 > >=20 > > That means if we land in the handler we know we're in either an incomin= g > > or outgoing migration and then you just have to check which? >=20 > Can save/load race with other QEMU code that might register/unregister > notifiers? I want to avoid having to introduce locking just for that. It looks like it can; qemu_savevm_state_setup is called from near the top of migration_thread, so I don't think it's holding locks at that point; and all the existing notifier changes on this notifier seem to be done from either init or vfio_open which I guess is under the big lock (?) Dave > --=20 > Thanks, >=20 > David / dhildenb -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK