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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BBA14CE79AC for ; Wed, 20 Sep 2023 07:46:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233998AbjITHqu (ORCPT ); Wed, 20 Sep 2023 03:46:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35506 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234001AbjITHqU (ORCPT ); Wed, 20 Sep 2023 03:46:20 -0400 Received: from mgamail.intel.com (mgamail.intel.com [134.134.136.20]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C9ACFE8 for ; Wed, 20 Sep 2023 00:45:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1695195947; x=1726731947; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=9aISSy5Y6tM/5Mn3uS24TYyGdedLlI00cbNXlchHbQU=; b=l2Xh1rwslYrzpiC9dAqARlRahanGE3c9AzAnOMGswCW9Onjo00YJoWEY riLhZXvySb5whOa16Gqd85cl/3PWjg+dv5gjccARCr72sIm2idczr6gxf tbF6MOaAriHCxWa15WukMPOn7sJQk3j9WY4pWdwqr7NL0c8VVCG3uzcYg SpV1846pID3a3RsF91ci0MM4v1bF2ZJszvM3yCKWTjGJMYpOAK6NsYORx bzIRcU3WMRf2IBh5nb0uGyI3WUXMVu9XxAeWrMMsJQQ3uWe4xR1Un/G+h T2zaRFyEAi6kUFln8vQLG47jZeQOdpeVzC/cnDULhB74KJtWPvvaUMREs g==; X-IronPort-AV: E=McAfee;i="6600,9927,10838"; a="370468073" X-IronPort-AV: E=Sophos;i="6.02,161,1688454000"; d="scan'208";a="370468073" Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Sep 2023 00:45:47 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10838"; a="749789384" X-IronPort-AV: E=Sophos;i="6.02,161,1688454000"; d="scan'208";a="749789384" Received: from lingshan-mobl.ccr.corp.intel.com (HELO [10.93.14.5]) ([10.93.14.5]) by fmsmga007-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Sep 2023 00:45:41 -0700 Message-ID: <1a2537e9-b70c-0d85-20f5-e8ef5c8a9bb8@intel.com> Date: Wed, 20 Sep 2023 15:45:38 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Firefox/102.0 Thunderbird/102.15.1 Subject: Re: [virtio-dev] Re: [virtio-comment] Re: [VIRTIO PCI PATCH v5 1/1] transport-pci: Add freeze_mode to virtio_pci_common_cfg Content-Language: en-US To: Parav Pandit , "Chen, Jiqian" , "Michael S. Tsirkin" Cc: Gerd Hoffmann , Jason Wang , Xuan Zhuo , David Airlie , Gurchetan Singh , Chia-I Wu , =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= , Robert Beckett , Mikhail Golubev-Ciuchea , "virtio-comment@lists.oasis-open.org" , "virtio-dev@lists.oasis-open.org" , "qemu-devel@nongnu.org" , "linux-kernel@vger.kernel.org" , Stefano Stabellini , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , "Deucher, Alexander" , "Koenig, Christian" , "Hildebrand, Stewart" , Xenia Ragiadakou , "Huang, Honglei1" , "Zhang, Julia" , "Huang, Ray" References: <20230919114242.2283646-1-Jiqian.Chen@amd.com> <20230919114242.2283646-2-Jiqian.Chen@amd.com> <20230919082802-mutt-send-email-mst@kernel.org> <701bb67c-c52d-4eb3-a6ed-f73bd5d0ff33@intel.com> <91c3e7ec-d702-ee61-c420-59ddc8dac6dc@intel.com> From: "Zhu, Lingshan" In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/20/2023 3:32 PM, Parav Pandit wrote: > >> From: Zhu, Lingshan >> Sent: Wednesday, September 20, 2023 12:58 PM >> >> On 9/20/2023 3:10 PM, Parav Pandit wrote: >>>> From: Zhu, Lingshan >>>> Sent: Wednesday, September 20, 2023 12:37 PM >>>>> The problem to overcome in [1] is, resume operation needs to be >>>>> synchronous >>>> as it involves large part of context to resume back, and hence just >>>> asynchronously setting DRIVER_OK is not enough. >>>>> The sw must verify back that device has resumed the operation and >>>>> ready to >>>> answer requests. >>>> this is not live migration, all device status and other information >>>> still stay in the device, no need to "resume" context, just resume running. >>>> >>> I am aware that it is not live migration. :) >>> >>> "Just resuming" involves lot of device setup task. The device implementation >> does not know for how long a device is suspended. >>> So for example, a VM is suspended for 6 hours, hence the device context >> could be saved in a slow disk. >>> Hence, when the resume is done, it needs to setup things again and driver got >> to verify before accessing more from the device. >> The restore procedures should perform by the hypervisor and done before set >> DRIVER_OK and wake up the guest. > Which is the signal to trigger the restore? Which is the trigger in physical device when there is no hypervisor? > > In my view, setting the DRIVER_OK is the signal regardless of hypervisor or physical device. > Hence the re-read is must. Yes, as I said below, should verify by re-read. > >> And the hypervisor/driver needs to check the device status by re-reading. >>>> Like resume from a failed LM. >>>>> This is slightly different flow than setting the DRIVER_OK for the >>>>> first time >>>> device initialization sequence as it does not involve large restoration. >>>>> So, to merge two ideas, instead of doing DRIVER_OK to resume, the >>>>> driver >>>> should clear the SUSPEND bit and verify that it is out of SUSPEND. >>>>> Because driver is still in _OK_ driving the device flipping the SUSPEND bit. >>>> Please read the spec, it says: >>>> The driver MUST NOT clear a device status bit >>>> >>> Yes, this is why either DRIER_OK validation by the driver is needed or Jiqian's >> synchronous new register.. >> so re-read > Yes. re-read until set, Thanks. >