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charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Wed, Mar 30, 2022 at 02:12:57PM +0000, Tian, Kevin wrote: > > From: Jason Gunthorpe > > Sent: Wednesday, March 30, 2022 7:58 PM > > > > On Wed, Mar 30, 2022 at 06:50:11AM +0000, Tian, Kevin wrote: > > > > > One thing that I'm not very sure is about DMA alias. Even when physically > > > there is only a single device within the group the aliasing could lead > > > to multiple RIDs in the group making it non-singleton. But probably we > > > don't need support SVA on such device until a real demand comes? > > > > How can we have multiple RIDs in the same group and have only one > > device in the group? > > Alex may help throw some insight here. Per what I read from the code > looks like certain device can generate traffic with multiple RIDs. IIRC "dma alias" refers to things like legacy PCI to PCIe bridges that do still have multiple PCI ID's behind the bridge used in configuration cycles however the PCI to PCIe bridge will tag all PCIe TLPs with its own RID because classic PCI has no way for the requestor to convey a RID to the bridge. So, from a Linux perspective the group should have have multiple struct devices behind the bridge, the bridge itself, and the RID the IOMMU HW matches on is only the RID of the PCI bridge. But we know this because we know there is classic PCI stuff in the heigharchy, so we can just mark that group as incompatible. > > Add a flag to the group that positively indicates the group can never > > have more than one member, even after hot plug. eg because it is > > impossible due to ACS, or lack of bridges, and so on. > > OK, I see your point. It essentially refers to a singleton group which > is immutable to hotplug. Yes, known at creation time, not retroactively enforced because someone used SVA Jason _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu 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 6D6B1C433F5 for ; Wed, 30 Mar 2022 14:30:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346862AbiC3Ob6 (ORCPT ); Wed, 30 Mar 2022 10:31:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60016 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230040AbiC3Ob5 (ORCPT ); Wed, 30 Mar 2022 10:31:57 -0400 Received: from NAM11-DM6-obe.outbound.protection.outlook.com (mail-dm6nam11on2071.outbound.protection.outlook.com [40.107.223.71]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0515240926 for ; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?0shwvUipBsPO6sEvDnOuVdfbSP/R7WcHnEXiEwgi0Ik2/79qfmK8yaHFsgIT?= =?us-ascii?Q?c4ZJAUOPs52hqEwuWgrJukdoL18WNPYwcCERoYQMLx+bTLV6tlhypLcE+M7Q?= =?us-ascii?Q?SBpfD64X+BQNMlOOzLUEwTn1tNLaUhHU5wbxheJMPlsFEkawDPyC7BitGDWA?= =?us-ascii?Q?F9COf8NqMoOBKKSgdxm9vj+adt3kdUyIrYYQw+SOB4wfGivEuKXlYT8FHdW8?= =?us-ascii?Q?9/sF40LUEDe+Rt5EWam3U6kCHziO+EOpkLuzqpg4DgLqLSZynnBvRXqDby89?= =?us-ascii?Q?kzDin/GYh+xR/NzizBw3vxgEpESy2gwIuEp6sH1vKXjUj2UfQlZb64Js/3n/?= =?us-ascii?Q?9e4wv4Pu/ZV5r0bVXliod0/twQZgH0iSniyfZpGdV7JpiLuZOdn0m+N5B0tI?= =?us-ascii?Q?YMcmN+RpA/+i3ChVC3UGNl7+V90mVQRdFQWemeeeJKUeQIQsTpBEcaDI50Xx?= =?us-ascii?Q?xrilzd7RYXuYxMTTlvRg+k81kK5gesV+U2hMQa4JZryZHSLobwBYsx/lDMpr?= =?us-ascii?Q?Wu1Bj8A6XcLVqjXwgPePUYd9fUNcxJOlSNr66ik1BhXLI7U7Q6VXSX8iFCj3?= =?us-ascii?Q?gensJKI453EHytHsBvSprLfegqrJ6FZgRFVZ+ADusXmH/zmTxeCE6zYfPNip?= =?us-ascii?Q?3jtHcWogkW+uYU9dGpy/l7DQOOqEKUfGXtxxhSrX0HTor4u1Q1LQS/JusAF7?= =?us-ascii?Q?DuX2ihWS3j6iiu0fxqWOgk7OD4SyzNJ2a1K2BYVA991IMchXM2X+LjHQjEny?= =?us-ascii?Q?0bTlRRgLGSCesb61SqgApt0cUYRZOo26/KLcs7dWeeIFsdmPS7ZjL79lD3eK?= =?us-ascii?Q?CvdlDQPDUWKfTMNwzhQ32vg+Bd64LWKUx0m4jA3Hw17neaW6WmplapksGKpG?= =?us-ascii?Q?PsVHNyFPnubzl7llWMaV8ZR/w0L2fEt19XknF/7uRAX20EqtBOLP8odUmblY?= =?us-ascii?Q?bryQTy1GD6ijGvdsci2XsNCoQaT3bdeDVJB8/I4YdrlCCFr7FTLyplqu1ZEy?= =?us-ascii?Q?Yqg0/XdOOE0dF6FCSiI7Kmzcg+kWR1blno4n3QX23jsbFV811WSnACORXWtx?= =?us-ascii?Q?SfUSDi6i9yUcaCPg5wEjguZr0ZUQVz14kQA+2Ym5e6IwzXuBTRuwYw69la0w?= =?us-ascii?Q?PFx0rueYR8rz0MvI2aZC1pLu62/NoFzV91GJP7VLXjcyHTQP7dvgcCsg3sKY?= =?us-ascii?Q?Yt6UbmQyRVMCn/zPK3EtVzMi//7XwjyZ9H3a1gB4at3xd0loHS2orbNCmU6M?= =?us-ascii?Q?3H+fr/qgD6eQoc1gAyCGVofJEPyvnn0oUYHKGO7pN/PfG3PmISI+wXutlnto?= =?us-ascii?Q?hbaKEeRqKBtd79MjUI/l+vwyug5bf6Boi+6Bgw287SlD8UbcWIprY9y1qWOv?= =?us-ascii?Q?3RLVqeikhfjjo8wRu9yd5muCWunwmGIkZ2Yl2TKDI5DKdYY9J96gC2zVqJHl?= =?us-ascii?Q?mhYlpdl9ZRpIKC7Czwg8AfeX1tEaaz3FL5wHM/96sm8keHo30VCsNoudWPb5?= =?us-ascii?Q?jDn35bfkU3TN/azINL33nsrlKgGUwhv7k3dIz9b4+P97ohRD+oFKbzVjV7z/?= =?us-ascii?Q?DQWsHW0R/8gqHyDC/JroQl0yZLQJHy8OrcrMjjjbaI6yzVRAyc4MHz8b9Qsj?= =?us-ascii?Q?IsHMjxhrBIpcmdhk5QjS16iMjYZPg/EhaKhyAGcWU69X9A01vz5dFBpv2edC?= =?us-ascii?Q?+3ujxn3hyGFdIc3FI05C0GVul5BK4R1L4xOe4QGVagiuBKVcgBLqf+s9PSKo?= =?us-ascii?Q?MQ/ojIQDUQ=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: a4d04116-715a-4cb7-70d5-08da1259cb4c X-MS-Exchange-CrossTenant-AuthSource: MN2PR12MB4192.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Mar 2022 14:30:10.0082 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: Gv8x8UmjCstkeG1OCzhagjJ2s7RWAgFFDWnuCUNU9acJ0MbjzHYnZstpg3aXsCfd X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR12MB4602 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 30, 2022 at 02:12:57PM +0000, Tian, Kevin wrote: > > From: Jason Gunthorpe > > Sent: Wednesday, March 30, 2022 7:58 PM > > > > On Wed, Mar 30, 2022 at 06:50:11AM +0000, Tian, Kevin wrote: > > > > > One thing that I'm not very sure is about DMA alias. Even when physically > > > there is only a single device within the group the aliasing could lead > > > to multiple RIDs in the group making it non-singleton. But probably we > > > don't need support SVA on such device until a real demand comes? > > > > How can we have multiple RIDs in the same group and have only one > > device in the group? > > Alex may help throw some insight here. Per what I read from the code > looks like certain device can generate traffic with multiple RIDs. IIRC "dma alias" refers to things like legacy PCI to PCIe bridges that do still have multiple PCI ID's behind the bridge used in configuration cycles however the PCI to PCIe bridge will tag all PCIe TLPs with its own RID because classic PCI has no way for the requestor to convey a RID to the bridge. So, from a Linux perspective the group should have have multiple struct devices behind the bridge, the bridge itself, and the RID the IOMMU HW matches on is only the RID of the PCI bridge. But we know this because we know there is classic PCI stuff in the heigharchy, so we can just mark that group as incompatible. > > Add a flag to the group that positively indicates the group can never > > have more than one member, even after hot plug. eg because it is > > impossible due to ACS, or lack of bridges, and so on. > > OK, I see your point. It essentially refers to a singleton group which > is immutable to hotplug. Yes, known at creation time, not retroactively enforced because someone used SVA Jason