From patchwork Tue Mar 7 12:54:50 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Joao Martins X-Patchwork-Id: 13163392 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 00415C678D5 for ; Tue, 7 Mar 2023 12:57:01 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pZWrt-0006wv-V6; Tue, 07 Mar 2023 07:56:41 -0500 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 1pZWrY-0006XR-IG for qemu-devel@nongnu.org; Tue, 07 Mar 2023 07:56:21 -0500 Received: from mx0a-00069f02.pphosted.com ([205.220.165.32]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pZWrW-00058j-Qu for qemu-devel@nongnu.org; Tue, 07 Mar 2023 07:56:16 -0500 Received: from pps.filterd (m0246627.ppops.net [127.0.0.1]) by mx0b-00069f02.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 32783uVZ007683; Tue, 7 Mar 2023 12:56:13 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : mime-version : content-type : content-transfer-encoding; s=corp-2022-7-12; bh=Xel4ecbEPawZ38P8TKB/h9sUQWvBI6R7FLZBmhXQ7Bw=; b=kWFTIOxlYmwyIJKMQRKlvKrqLRNM+gNAgnbLFcCllO+kQKpu1wJcgxSWQ7R1im1eOehW 4STyuDOLMNYE+0UIPW6Ws99loEoQntvKfqmdT0LES0dLcq0ehQPTS5o7b+5/U8+vQ6O6 V1dLIsyJcJijuPXSswflfMyIOh3o4tZbjL9bDEcDf2oYJhTW0SzjK6x/JKeRYioIwqeX eJFwzP2LkOt8Rc97NZbqcFv9v5c2nico9wMZa2MOO/ugfKLDzFXJ2FUBKxOZMnjulPzg kCiW7FrJugxN1v6+yycKKg31E7XxPILefkvCb0P6HJ0rcNiM2enNV5QPFBtCAUAbDQVN cQ== Received: from iadpaimrmta02.imrmtpd1.prodappiadaev1.oraclevcn.com (iadpaimrmta02.appoci.oracle.com [147.154.18.20]) by mx0b-00069f02.pphosted.com (PPS) with ESMTPS id 3p5nn91pvq-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 07 Mar 2023 12:56:13 +0000 Received: from pps.filterd (iadpaimrmta02.imrmtpd1.prodappiadaev1.oraclevcn.com [127.0.0.1]) by iadpaimrmta02.imrmtpd1.prodappiadaev1.oraclevcn.com (8.17.1.5/8.17.1.5) with ESMTP id 327C8dnB029280; Tue, 7 Mar 2023 12:56:12 GMT Received: from pps.reinject (localhost [127.0.0.1]) by iadpaimrmta02.imrmtpd1.prodappiadaev1.oraclevcn.com (PPS) with ESMTPS id 3p4u1eyf7k-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 07 Mar 2023 12:56:12 +0000 Received: from iadpaimrmta02.imrmtpd1.prodappiadaev1.oraclevcn.com (iadpaimrmta02.imrmtpd1.prodappiadaev1.oraclevcn.com [127.0.0.1]) by pps.reinject (8.17.1.5/8.17.1.5) with ESMTP id 327CtV5T004358; Tue, 7 Mar 2023 12:56:11 GMT Received: from joaomart-mac.uk.oracle.com (dhcp-10-175-196-64.vpn.oracle.com [10.175.196.64]) by iadpaimrmta02.imrmtpd1.prodappiadaev1.oraclevcn.com (PPS) with ESMTP id 3p4u1eyefv-16; Tue, 07 Mar 2023 12:56:11 +0000 From: Joao Martins To: qemu-devel@nongnu.org Cc: Alex Williamson , Cedric Le Goater , Yishai Hadas , Jason Gunthorpe , Maor Gottlieb , Kirti Wankhede , Tarun Gupta , Avihai Horon , Joao Martins Subject: [PATCH v5 15/15] docs/devel: Document VFIO device dirty page tracking Date: Tue, 7 Mar 2023 12:54:50 +0000 Message-Id: <20230307125450.62409-16-joao.m.martins@oracle.com> In-Reply-To: <20230307125450.62409-1-joao.m.martins@oracle.com> References: <20230307125450.62409-1-joao.m.martins@oracle.com> MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.219,Aquarius:18.0.942,Hydra:6.0.573,FMLib:17.11.170.22 definitions=2023-03-07_06,2023-03-07_01,2023-02-09_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxscore=0 phishscore=0 bulkscore=0 adultscore=0 suspectscore=0 spamscore=0 mlxlogscore=990 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2212070000 definitions=main-2303070117 X-Proofpoint-GUID: FIGetVEgc3P-rAaqPRilCMbO_Ubuj6L3 X-Proofpoint-ORIG-GUID: FIGetVEgc3P-rAaqPRilCMbO_Ubuj6L3 Received-SPF: pass client-ip=205.220.165.32; envelope-from=joao.m.martins@oracle.com; helo=mx0a-00069f02.pphosted.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_MED=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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 Adjust the VFIO dirty page tracking documentation and add a section to describe device dirty page tracking. Signed-off-by: Avihai Horon Signed-off-by: Joao Martins Reviewed-by: Cédric Le Goater --- docs/devel/vfio-migration.rst | 46 +++++++++++++++++++++++------------ 1 file changed, 31 insertions(+), 15 deletions(-) diff --git a/docs/devel/vfio-migration.rst b/docs/devel/vfio-migration.rst index c214c73e2818..1b68ccf11529 100644 --- a/docs/devel/vfio-migration.rst +++ b/docs/devel/vfio-migration.rst @@ -59,22 +59,37 @@ System memory dirty pages tracking ---------------------------------- A ``log_global_start`` and ``log_global_stop`` memory listener callback informs -the VFIO IOMMU module to start and stop dirty page tracking. A ``log_sync`` -memory listener callback marks those system memory pages as dirty which are -used for DMA by the VFIO device. The dirty pages bitmap is queried per -container. All pages pinned by the vendor driver through external APIs have to -be marked as dirty during migration. When there are CPU writes, CPU dirty page -tracking can identify dirtied pages, but any page pinned by the vendor driver -can also be written by the device. There is currently no device or IOMMU -support for dirty page tracking in hardware. +the VFIO dirty tracking module to start and stop dirty page tracking. A +``log_sync`` memory listener callback queries the dirty page bitmap from the +dirty tracking module and marks system memory pages which were DMA-ed by the +VFIO device as dirty. The dirty page bitmap is queried per container. + +Currently there are two ways dirty page tracking can be done: +(1) Device dirty tracking: +In this method the device is responsible to log and report its DMAs. This +method can be used only if the device is capable of tracking its DMAs. +Discovering device capability, starting and stopping dirty tracking, and +syncing the dirty bitmaps from the device are done using the DMA logging uAPI. +More info about the uAPI can be found in the comments of the +``vfio_device_feature_dma_logging_control`` and +``vfio_device_feature_dma_logging_report`` structures in the header file +linux-headers/linux/vfio.h. + +(2) VFIO IOMMU module: +In this method dirty tracking is done by IOMMU. However, there is currently no +IOMMU support for dirty page tracking. For this reason, all pages are +perpetually marked dirty, unless the device driver pins pages through external +APIs in which case only those pinned pages are perpetually marked dirty. + +If the above two methods are not supported, all pages are perpetually marked +dirty by QEMU. By default, dirty pages are tracked during pre-copy as well as stop-and-copy -phase. So, a page pinned by the vendor driver will be copied to the destination -in both phases. Copying dirty pages in pre-copy phase helps QEMU to predict if -it can achieve its downtime tolerances. If QEMU during pre-copy phase keeps -finding dirty pages continuously, then it understands that even in stop-and-copy -phase, it is likely to find dirty pages and can predict the downtime -accordingly. +phase. So, a page marked as dirty will be copied to the destination in both +phases. Copying dirty pages in pre-copy phase helps QEMU to predict if it can +achieve its downtime tolerances. If QEMU during pre-copy phase keeps finding +dirty pages continuously, then it understands that even in stop-and-copy phase, +it is likely to find dirty pages and can predict the downtime accordingly. QEMU also provides a per device opt-out option ``pre-copy-dirty-page-tracking`` which disables querying the dirty bitmap during pre-copy phase. If it is set to @@ -89,7 +104,8 @@ phase of migration. In that case, the unmap ioctl returns any dirty pages in that range and QEMU reports corresponding guest physical pages dirty. During stop-and-copy phase, an IOMMU notifier is used to get a callback for mapped pages and then dirty pages bitmap is fetched from VFIO IOMMU modules for those -mapped ranges. +mapped ranges. If device dirty tracking is enabled with vIOMMU, live migration +will be blocked. Flow of state changes during Live migration ===========================================