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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 48148C282DD for ; Fri, 10 Jan 2020 14:21:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1F8FF20838 for ; Fri, 10 Jan 2020 14:21:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="UpAtD92W" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728080AbgAJOVi (ORCPT ); Fri, 10 Jan 2020 09:21:38 -0500 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:57740 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727746AbgAJOVh (ORCPT ); Fri, 10 Jan 2020 09:21:37 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1578666095; 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=XGXWI3monwW6hEW9z+N5Xg8fGIxYQC8MXY9UwxRNWf8=; b=UpAtD92WAvoyCIPlIyE3FVwtwQHeVxB2K7WmdN6dP1HPbee3OWuJHS14aD8qAVgq+l59zB YHAa54lSDHTEUYeXfk56YyNJ34GDGiRCJq5xZ9G/UAnb7Xn3RTt6o0MAqbuJoTrIb1TFjd CyM4lfWELi2drK0XkBpCHH3N7+zKblo= 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-344-3p3V5eZ6M_yHk9YIo3GFMg-1; Fri, 10 Jan 2020 09:21:22 -0500 X-MC-Unique: 3p3V5eZ6M_yHk9YIo3GFMg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7FDD218C35BC; Fri, 10 Jan 2020 14:21:20 +0000 (UTC) Received: from gondolin (dhcp-192-245.str.redhat.com [10.33.192.245]) by smtp.corp.redhat.com (Postfix) with ESMTP id C70EE87EC0; Fri, 10 Jan 2020 14:21:13 +0000 (UTC) Date: Fri, 10 Jan 2020 15:21:11 +0100 From: Cornelia Huck To: Alex Williamson Cc: Kirti Wankhede , "Dr. David Alan Gilbert" , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v10 Kernel 1/5] vfio: KABI for migration interface for device state Message-ID: <20200110152111.74c87595.cohuck@redhat.com> In-Reply-To: <20200108154428.02bb312d@w520.home> References: <1576527700-21805-1-git-send-email-kwankhede@nvidia.com> <1576527700-21805-2-git-send-email-kwankhede@nvidia.com> <20191216154406.023f912b@x1.home> <20191217114357.6496f748@x1.home> <3527321f-e310-8324-632c-339b22f15de5@nvidia.com> <20191219102706.0a316707@x1.home> <928e41b5-c3fd-ed75-abd6-ada05cda91c9@nvidia.com> <20191219140929.09fa24da@x1.home> <20200102182537.GK2927@work-vm> <20200106161851.07871e28@w520.home> <20200107100923.2f7b5597@w520.home> <08b7f953-6ac5-cd79-b1ff-54338da32d1e@nvidia.com> <20200107115602.25156c41@w520.home> <20200108155955.78e908c1.cohuck@redhat.com> <20200108113134.05c08470@w520.home> <46ac2d9e-4f4e-27d5-2a96-932c444e3461@nvidia.com> <20200108154428.02bb312d@w520.home> Organization: Red Hat GmbH MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, 8 Jan 2020 15:44:28 -0700 Alex Williamson wrote: > On Thu, 9 Jan 2020 02:11:11 +0530 > Kirti Wankhede wrote: > > > On 1/9/2020 12:01 AM, Alex Williamson wrote: > > > On Wed, 8 Jan 2020 15:59:55 +0100 > > > Cornelia Huck wrote: > > >> I think one thing we could do is start to tie the meaning more to the > > >> actual state (bit combination) and less to the individual bits. I.e. > > >> > > >> - bit 0 indicates 'running', > > >> - bit 1 indicates 'saving', > > >> - bit 2 indicates 'resuming', > > >> - bits 3-31 are reserved. [Aside: reserved-and-ignored or > > >> reserved-and-must-be-zero?] > > > > > > This version specified them as: > > > > > > Bits 3 - 31 are reserved for future use. User should perform > > > read-modify-write operation on this field. > > > > > > The intention is that the user should not make any assumptions about > > > the state of the reserved bits, but should preserve them when changing > > > known bits. Therefore I think it's ignored but preserved. If we > > > specify them as zero, then I think we lose any chance to define them > > > later. Nod. What about extending the description to: "Bits 3-31 are reserved for future use. In order to preserve them, a read-modify-write operation on this field should be used when modifying the specified bits." ? > > > > > >> [Note that I don't specify what happens when a bit is set or unset.] > > >> > > >> States are then defined as: > > >> 000b => stopped state (not saving or resuming) > > >> 001b => running state (not saving or resuming) > > >> 010b => stop-and-copy state > > >> 011b => pre-copy state > > >> 100b => resuming state > > >> > > >> [Transitions between these states defined, as before.] > > >> > > >> 101b => reserved [for post-copy; no transitions defined] > > >> 111b => reserved [state does not make sense; no transitions defined] > > >> 110b => error state [state does not make sense per se, but it does not > > >> indicate running; transitions into this state *are* possible] > > >> > > >> To a 'reserved' state, we can later assign a different meaning (we > > >> could even re-use 111b for a different error state, if needed); while > > >> the error state must always stay the error state. > > >> > > >> We should probably use some kind of feature indication to signify > > >> whether a 'reserved' state actually has a meaning. Also, maybe we also > > >> should designate the states > 111b as 'reserved'. > > >> > > >> Does that make sense? > > > > > > It seems you have an opinion to restrict this particular error state to > > > 110b rather than 11Xb, reserving 111b for some future error condition. > > > That's fine and I think we agree that using the state with _RUNNING set > > > to zero is more logical as we expect the device to be non-operational > > > in this state. Good. > > > > > > I'm also thinking more of these as states, but at the same time we're > > > not doing away with the bit definitions. I think the states are much > > > easier to decode and use if we think about the function of each bit, > > > which leads to the logical incongruity that the 11Xb states are > > > impossible and therefore must be error states. Yes, that's fine. > > > > > > > I agree on bit definition is better. > > > > Ok. Should there be a defined value for error, which can be used by > > vendor driver for error state? > > > > #define VFIO_DEVICE_STATE_ERROR \ > > (VFIO_DEVICE_STATE_SAVING | VFIO_DEVICE_STATE_RESUMING) > > Seems like a good idea for consistency. Thanks, > > Alex Agreed, I like that as well. 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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 21536C282DD for ; Fri, 10 Jan 2020 14:22:17 +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 DDA7F2077C for ; Fri, 10 Jan 2020 14:22:16 +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="UpAtD92W" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DDA7F2077C 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]:46094 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ipvB2-000663-3Q for qemu-devel@archiver.kernel.org; Fri, 10 Jan 2020 09:22:16 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:50531) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ipvAP-0005Tm-KD for qemu-devel@nongnu.org; Fri, 10 Jan 2020 09:21:38 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ipvAO-0000Xz-Ba for qemu-devel@nongnu.org; Fri, 10 Jan 2020 09:21:37 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:57137 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 1ipvAO-0000W4-6E for qemu-devel@nongnu.org; Fri, 10 Jan 2020 09:21:36 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1578666095; 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=XGXWI3monwW6hEW9z+N5Xg8fGIxYQC8MXY9UwxRNWf8=; b=UpAtD92WAvoyCIPlIyE3FVwtwQHeVxB2K7WmdN6dP1HPbee3OWuJHS14aD8qAVgq+l59zB YHAa54lSDHTEUYeXfk56YyNJ34GDGiRCJq5xZ9G/UAnb7Xn3RTt6o0MAqbuJoTrIb1TFjd CyM4lfWELi2drK0XkBpCHH3N7+zKblo= 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-344-3p3V5eZ6M_yHk9YIo3GFMg-1; Fri, 10 Jan 2020 09:21:22 -0500 X-MC-Unique: 3p3V5eZ6M_yHk9YIo3GFMg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7FDD218C35BC; Fri, 10 Jan 2020 14:21:20 +0000 (UTC) Received: from gondolin (dhcp-192-245.str.redhat.com [10.33.192.245]) by smtp.corp.redhat.com (Postfix) with ESMTP id C70EE87EC0; Fri, 10 Jan 2020 14:21:13 +0000 (UTC) Date: Fri, 10 Jan 2020 15:21:11 +0100 From: Cornelia Huck To: Alex Williamson Subject: Re: [PATCH v10 Kernel 1/5] vfio: KABI for migration interface for device state Message-ID: <20200110152111.74c87595.cohuck@redhat.com> In-Reply-To: <20200108154428.02bb312d@w520.home> References: <1576527700-21805-1-git-send-email-kwankhede@nvidia.com> <1576527700-21805-2-git-send-email-kwankhede@nvidia.com> <20191216154406.023f912b@x1.home> <20191217114357.6496f748@x1.home> <3527321f-e310-8324-632c-339b22f15de5@nvidia.com> <20191219102706.0a316707@x1.home> <928e41b5-c3fd-ed75-abd6-ada05cda91c9@nvidia.com> <20191219140929.09fa24da@x1.home> <20200102182537.GK2927@work-vm> <20200106161851.07871e28@w520.home> <20200107100923.2f7b5597@w520.home> <08b7f953-6ac5-cd79-b1ff-54338da32d1e@nvidia.com> <20200107115602.25156c41@w520.home> <20200108155955.78e908c1.cohuck@redhat.com> <20200108113134.05c08470@w520.home> <46ac2d9e-4f4e-27d5-2a96-932c444e3461@nvidia.com> <20200108154428.02bb312d@w520.home> Organization: Red Hat GmbH MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] 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: kevin.tian@intel.com, yi.l.liu@intel.com, cjia@nvidia.com, kvm@vger.kernel.org, eskultet@redhat.com, ziye.yang@intel.com, qemu-devel@nongnu.org, Zhengxiao.zx@alibaba-inc.com, shuangtai.tst@alibaba-inc.com, "Dr. David Alan Gilbert" , zhi.a.wang@intel.com, mlevitsk@redhat.com, pasic@linux.ibm.com, aik@ozlabs.ru, Kirti Wankhede , eauger@redhat.com, felipe@nutanix.com, jonathan.davies@nutanix.com, yan.y.zhao@intel.com, changpeng.liu@intel.com, Ken.Xue@amd.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 8 Jan 2020 15:44:28 -0700 Alex Williamson wrote: > On Thu, 9 Jan 2020 02:11:11 +0530 > Kirti Wankhede wrote: > > > On 1/9/2020 12:01 AM, Alex Williamson wrote: > > > On Wed, 8 Jan 2020 15:59:55 +0100 > > > Cornelia Huck wrote: > > >> I think one thing we could do is start to tie the meaning more to the > > >> actual state (bit combination) and less to the individual bits. I.e. > > >> > > >> - bit 0 indicates 'running', > > >> - bit 1 indicates 'saving', > > >> - bit 2 indicates 'resuming', > > >> - bits 3-31 are reserved. [Aside: reserved-and-ignored or > > >> reserved-and-must-be-zero?] > > > > > > This version specified them as: > > > > > > Bits 3 - 31 are reserved for future use. User should perform > > > read-modify-write operation on this field. > > > > > > The intention is that the user should not make any assumptions about > > > the state of the reserved bits, but should preserve them when changing > > > known bits. Therefore I think it's ignored but preserved. If we > > > specify them as zero, then I think we lose any chance to define them > > > later. Nod. What about extending the description to: "Bits 3-31 are reserved for future use. In order to preserve them, a read-modify-write operation on this field should be used when modifying the specified bits." ? > > > > > >> [Note that I don't specify what happens when a bit is set or unset.] > > >> > > >> States are then defined as: > > >> 000b => stopped state (not saving or resuming) > > >> 001b => running state (not saving or resuming) > > >> 010b => stop-and-copy state > > >> 011b => pre-copy state > > >> 100b => resuming state > > >> > > >> [Transitions between these states defined, as before.] > > >> > > >> 101b => reserved [for post-copy; no transitions defined] > > >> 111b => reserved [state does not make sense; no transitions defined] > > >> 110b => error state [state does not make sense per se, but it does not > > >> indicate running; transitions into this state *are* possible] > > >> > > >> To a 'reserved' state, we can later assign a different meaning (we > > >> could even re-use 111b for a different error state, if needed); while > > >> the error state must always stay the error state. > > >> > > >> We should probably use some kind of feature indication to signify > > >> whether a 'reserved' state actually has a meaning. Also, maybe we also > > >> should designate the states > 111b as 'reserved'. > > >> > > >> Does that make sense? > > > > > > It seems you have an opinion to restrict this particular error state to > > > 110b rather than 11Xb, reserving 111b for some future error condition. > > > That's fine and I think we agree that using the state with _RUNNING set > > > to zero is more logical as we expect the device to be non-operational > > > in this state. Good. > > > > > > I'm also thinking more of these as states, but at the same time we're > > > not doing away with the bit definitions. I think the states are much > > > easier to decode and use if we think about the function of each bit, > > > which leads to the logical incongruity that the 11Xb states are > > > impossible and therefore must be error states. Yes, that's fine. > > > > > > > I agree on bit definition is better. > > > > Ok. Should there be a defined value for error, which can be used by > > vendor driver for error state? > > > > #define VFIO_DEVICE_STATE_ERROR \ > > (VFIO_DEVICE_STATE_SAVING | VFIO_DEVICE_STATE_RESUMING) > > Seems like a good idea for consistency. Thanks, > > Alex Agreed, I like that as well.