From patchwork Mon Sep 11 07:50:07 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?C=C3=A9dric_Le_Goater?= X-Patchwork-Id: 13378934 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 43AC4EE7FF4 for ; Mon, 11 Sep 2023 07:51:52 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qfbh8-0004Ox-Mw; Mon, 11 Sep 2023 03:50:54 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qfbgy-00047y-5F for qemu-devel@nongnu.org; Mon, 11 Sep 2023 03:50:45 -0400 Received: from gandalf.ozlabs.org ([150.107.74.76]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qfbgv-0008Ej-Sh for qemu-devel@nongnu.org; Mon, 11 Sep 2023 03:50:43 -0400 Received: from gandalf.ozlabs.org (gandalf.ozlabs.org [150.107.74.76]) by gandalf.ozlabs.org (Postfix) with ESMTP id 4Rkf5r4dzjz4xNG; Mon, 11 Sep 2023 17:50:40 +1000 (AEST) Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mail.ozlabs.org (Postfix) with ESMTPSA id 4Rkf5p6JKtz4xM5; Mon, 11 Sep 2023 17:50:38 +1000 (AEST) From: =?utf-8?q?C=C3=A9dric_Le_Goater?= To: qemu-devel@nongnu.org Cc: Alex Williamson , Avihai Horon , Peter Xu , =?utf-8?q?C=C3=A9dric_Le_Goater?= Subject: [PULL 12/13] vfio/migration: Block VFIO migration with background snapshot Date: Mon, 11 Sep 2023 09:50:07 +0200 Message-ID: <20230911075008.462712-13-clg@redhat.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230911075008.462712-1-clg@redhat.com> References: <20230911075008.462712-1-clg@redhat.com> MIME-Version: 1.0 Received-SPF: pass client-ip=150.107.74.76; envelope-from=SRS0=GLJ6=E3=redhat.com=clg@ozlabs.org; helo=gandalf.ozlabs.org X-Spam_score_int: -16 X-Spam_score: -1.7 X-Spam_bar: - X-Spam_report: (-1.7 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.249, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org From: Avihai Horon Background snapshot allows creating a snapshot of the VM while it's running and keeping it small by not including dirty RAM pages. The way it works is by first stopping the VM, saving the non-iterable devices' state and then starting the VM and saving the RAM while write protecting it with UFFD. The resulting snapshot represents the VM state at snapshot start. VFIO migration is not compatible with background snapshot. First of all, VFIO device state is not even saved in background snapshot because only non-iterable device state is saved. But even if it was saved, after starting the VM, a VFIO device could dirty pages without it being detected by UFFD write protection. This would corrupt the snapshot, as the RAM in it would not represent the RAM at snapshot start. To prevent this, block VFIO migration with background snapshot. Signed-off-by: Avihai Horon Reviewed-by: Peter Xu Signed-off-by: Cédric Le Goater --- hw/vfio/migration.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c index 20994dc1d60b1606728415fec17c19cfd00c4dee..da43dcd2fe0734091960e3eb2ffa26750073be72 100644 --- a/hw/vfio/migration.c +++ b/hw/vfio/migration.c @@ -340,7 +340,8 @@ static int vfio_save_prepare(void *opaque, Error **errp) VFIODevice *vbasedev = opaque; /* - * Snapshot doesn't use postcopy, so allow snapshot even if postcopy is on. + * Snapshot doesn't use postcopy nor background snapshot, so allow snapshot + * even if they are on. */ if (runstate_check(RUN_STATE_SAVE_VM)) { return 0; @@ -353,6 +354,14 @@ static int vfio_save_prepare(void *opaque, Error **errp) return -EOPNOTSUPP; } + if (migrate_background_snapshot()) { + error_setg( + errp, + "%s: VFIO migration is not supported with background snapshot", + vbasedev->name); + return -EOPNOTSUPP; + } + return 0; }