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 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 DA16CCE79AD for ; Wed, 20 Sep 2023 07:46:12 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qiruH-0005Br-Cl; Wed, 20 Sep 2023 03:45:57 -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 1qiruC-0005Am-AW for qemu-devel@nongnu.org; Wed, 20 Sep 2023 03:45:55 -0400 Received: from mgamail.intel.com ([134.134.136.20]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qiru9-0007Cb-Ge for qemu-devel@nongnu.org; Wed, 20 Sep 2023 03:45:51 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1695195949; x=1726731949; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=9aISSy5Y6tM/5Mn3uS24TYyGdedLlI00cbNXlchHbQU=; b=HSNdF5ElFmOsVX/T4jDLvm+m+GQS5PetBLhWpG4l41DS2tHUmRbQD8gu tdN0hrT71/aTSMZ+/+uOivvweqhtCymUW6jDA9BREex9FhG+ie562DdJv 5VKznWEPlTagvp+lj+/D4bZNYHwkWJZuG0w1QiHY+3SvRlv+ZHWjt/grL Kynwu/1v7smbL0uPHXZU5T9CTOrXohgrdbWuwQ4xGeYmRP91fFuX4Gl3P c+U7HJ1APMNw4MaDIdZzsatjHvPO1gO3sKZO4CCHlk/2MEuU6HqvADF+w LxZ/njKybD6jJezLp3pUrf8N5aYn7w/pryx+xLrRV4Px5nWjpqPPcQRcr g==; X-IronPort-AV: E=McAfee;i="6600,9927,10838"; a="370468081" X-IronPort-AV: E=Sophos;i="6.02,161,1688454000"; d="scan'208";a="370468081" 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 Received-SPF: pass client-ip=134.134.136.20; envelope-from=lingshan.zhu@intel.com; helo=mgamail.intel.com X-Spam_score_int: -58 X-Spam_score: -5.9 X-Spam_bar: ----- X-Spam_report: (-5.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-1.473, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=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 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. >