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 7F47EC4345F for ; Wed, 17 Apr 2024 12:00:47 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rx3xM-0001Zt-Rt; Wed, 17 Apr 2024 08:00:05 -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 1rx3xK-0001ZZ-Hi for qemu-devel@nongnu.org; Wed, 17 Apr 2024 08:00:02 -0400 Received: from frasgout.his.huawei.com ([185.176.79.56]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rx3xH-00055A-Ef for qemu-devel@nongnu.org; Wed, 17 Apr 2024 08:00:02 -0400 Received: from mail.maildlp.com (unknown [172.18.186.31]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4VKKD05Wb7z6H6mb; Wed, 17 Apr 2024 19:57:52 +0800 (CST) Received: from lhrpeml500005.china.huawei.com (unknown [7.191.163.240]) by mail.maildlp.com (Postfix) with ESMTPS id A0CE41406AC; Wed, 17 Apr 2024 19:59:52 +0800 (CST) Received: from localhost (10.202.227.76) by lhrpeml500005.china.huawei.com (7.191.163.240) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.1.2507.35; Wed, 17 Apr 2024 12:59:52 +0100 Date: Wed, 17 Apr 2024 12:59:51 +0100 To: fan CC: Gregory Price , , , , , , , , , , , Fan Ni Subject: Re: [PATCH v6 10/12] hw/mem/cxl_type3: Add dpa range validation for accesses to DC regions Message-ID: <20240417125951.00001db1@Huawei.com> In-Reply-To: References: <20240325190339.696686-1-nifan.cxl@gmail.com> <20240325190339.696686-11-nifan.cxl@gmail.com> <20240416160056.0000325c@Huawei.com> Organization: Huawei Technologies Research and Development (UK) Ltd. X-Mailer: Claws Mail 4.1.0 (GTK 3.24.33; x86_64-w64-mingw32) MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Originating-IP: [10.202.227.76] X-ClientProxiedBy: lhrpeml500001.china.huawei.com (7.191.163.213) To lhrpeml500005.china.huawei.com (7.191.163.240) Received-SPF: pass client-ip=185.176.79.56; envelope-from=jonathan.cameron@huawei.com; helo=frasgout.his.huawei.com X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, 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: , Reply-to: Jonathan Cameron From: Jonathan Cameron via Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, 16 Apr 2024 09:37:09 -0700 fan wrote: > On Tue, Apr 16, 2024 at 04:00:56PM +0100, Jonathan Cameron wrote: > > On Mon, 15 Apr 2024 10:37:00 -0700 > > fan wrote: > > =20 > > > On Fri, Apr 12, 2024 at 06:54:42PM -0400, Gregory Price wrote: =20 > > > > On Mon, Mar 25, 2024 at 12:02:28PM -0700, nifan.cxl@gmail.com wrote= : =20 > > > > > From: Fan Ni > > > > >=20 > > > > > All dpa ranges in the DC regions are invalid to access until an e= xtent > > > > > covering the range has been added. Add a bitmap for each region to > > > > > record whether a DC block in the region has been backed by DC ext= ent. > > > > > For the bitmap, a bit in the bitmap represents a DC block. When a= DC > > > > > extent is added, all the bits of the blocks in the extent will be= set, > > > > > which will be cleared when the extent is released. > > > > >=20 > > > > > Reviewed-by: Jonathan Cameron > > > > > Signed-off-by: Fan Ni > > > > > --- > > > > > hw/cxl/cxl-mailbox-utils.c | 6 +++ > > > > > hw/mem/cxl_type3.c | 76 +++++++++++++++++++++++++++++++= ++++++ > > > > > include/hw/cxl/cxl_device.h | 7 ++++ > > > > > 3 files changed, 89 insertions(+) > > > > >=20 > > > > > diff --git a/hw/cxl/cxl-mailbox-utils.c b/hw/cxl/cxl-mailbox-util= s.c > > > > > index 7094e007b9..a0d2239176 100644 > > > > > --- a/hw/cxl/cxl-mailbox-utils.c > > > > > +++ b/hw/cxl/cxl-mailbox-utils.c > > > > > @@ -1620,6 +1620,7 @@ static CXLRetCode cmd_dcd_add_dyn_cap_rsp(c= onst struct cxl_cmd *cmd, > > > > > =20 > > > > > cxl_insert_extent_to_extent_list(extent_list, dpa, len, = NULL, 0); > > > > > ct3d->dc.total_extent_count +=3D 1; > > > > > + ct3_set_region_block_backed(ct3d, dpa, len); > > > > > =20 > > > > > ent =3D QTAILQ_FIRST(&ct3d->dc.extents_pending); > > > > > cxl_remove_extent_from_extent_list(&ct3d->dc.extents_pen= ding, ent); =20 > > > >=20 > > > > while looking at the MHD code, we had decided to "reserve" the bloc= ks in > > > > the bitmap in the call to `qmp_cxl_process_dynamic_capacity` in ord= er to > > > > prevent a potential double-allocation (basically we need to sanity = check > > > > that two hosts aren't reserving the region PRIOR to the host being > > > > notified). > > > >=20 > > > > I did not see any checks in the `qmp_cxl_process_dynamic_capacity` = path > > > > to prevent pending extents from being double-allocated. Is this an > > > > explicit choice? > > > >=20 > > > > I can see, for example, why you may want to allow the following in = the > > > > pending list: [Add X, Remove X, Add X]. I just want to know if thi= s is > > > > intentional or not. If not, you may consider adding a pending check > > > > during the sanity check phase of `qmp_cxl_process_dynamic_capacity` > > > >=20 > > > > ~Gregory =20 > > >=20 > > > First, for remove request, pending list is not involved. See cxl r3.1, > > > 9.13.3.3. Pending basically means "pending to add".=20 > > > So for the above example, in the pending list, you can see [Add x, ad= d x] if the > > > event is not processed in time. > > > Second, from the spec, I cannot find any text saying we cannot issue > > > another add extent X if it is still pending. =20 > >=20 > > I think there is text saying that the capacity is not released for reuse > > by the device until it receives a response from the host. Whilst > > it's not explicit on offers to the same host, I'm not sure that matters. > > So I don't think it is suppose to queue multiple extents... =20 >=20 > Are you suggesting we add a check here to reject the second add when the > first one is still pending? Yes. The capacity is not back with the device to reissue. On an MH-MLD/SLD we'd need to prevent it being added (not shared) to multip= le hosts, this is kind of the temporal equivalent of that. >=20 > Currently, we do not allow releasing an extent when it is still pending, > which aligns with the case you mentioned above "not release for reuse", I > think. > Can the second add mean a retry instead of reuse?=20 No - or at least the device should not be doing that. The FM might try again, but only once it knows try 1 failed. For reasons of this aligning with MHD case where you definitely can't offer it to more than one host, I think we should not do it. Whether we should put any effort into blocking it is a different question. User error :) Note, the host must not remove a log entry until it has dealt with it (sent a response) so there is no obvious reason to bother with a retry. Maybe a booting host would reject all offered extents (because it's not rea= dy for them yet), but then I'd want the FM to explicitly decide to tell the de= vice to offer gain. Whilst this is a custom interface, the equivalent FM API does say. "The command, with selection policy Enable Shared Access, shall also fail w= ith Invalid Input under the following conditions: =E2=80=A2 When the specified region is not Sharable =E2=80=A2 When the tagged capacity is already mapped to any Host ID via a n= on-Sharable region =E2=80=A2 When the tagged capacity cannot be added to the requested region = due to deviceimposed restrictions =E2=80=A2 When the same tagged capacity is currently accessible by the same= LD" Little fuzzy because of the whole pending vs 'mapped / accessible' wording = but I think intent is you can't send again until first one is dealt with. Jonathan >=20 > Fan >=20 > >=20 > > =20 > > > From the kernel side, if the first one is accepted, the second one wi= ll > > > get rejected, and there is no issue there. > > > If the first is reject for some reason, the second one can get > > > accepted or rejected and do not need to worry about the first one. > > >=20 > > >=20 > > > Fan > > > =20 > > =20