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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: BN9PR11MB5276.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: fb1acf96-5417-42b5-f5e1-08da08a2c691 X-MS-Exchange-CrossTenant-originalarrivaltime: 18 Mar 2022 05:47:23.4119 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: sKITXmdHnMpj32SPN8Xe375P5/iUoJPpoVPf3Ws1G/UrqMUp9nuDqORKKJRgiA5Bi1M4rbugzV48/4ucxkYzdw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN2PR11MB4351 X-OriginatorOrg: intel.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > From: Jason Gunthorpe > Sent: Thursday, March 17, 2022 8:04 AM >=20 > On Wed, Mar 16, 2022 at 10:23:26PM +0000, Luck, Tony wrote: >=20 > > Kernel users (ring0) can supply any PASID when they use > > the ENQCMDS instruction. Is that what you mean when you > > say "real applications"? >=20 > I'm not talking about ENQCMD at all >=20 > I'm saying I don't see much utility to have two PASIDs assigned to the > same device that perform the same IOVA translation. >=20 > So I would expect the list of attachments in an iommu_domain to have > exactly one device in it and multiple PASIDs to the same device from > the same iommu_domain is a oddball corner case we don't need to > optimize for, beyond being able to allow it to happen. >=20 In theory we do have one example with SIOV. Say two mdev's of a same parent device are assigned to a guest and each mdev gets a unique PASID to tag the vRID requests. Then the guest attaches both mdev's to a stage-1 IOVA domain via vIOMMU, e.g. when it further assigns them to an user application. In this case the host iommu_domain wrapping the stage-1 page table is attached by two PASIDs of the same device. However iirc there are other tricky issues blocking this usage (Jacob may remember more detail here) and we didn't hear strong interest from customer on it. So this is just FYI for theoretical possibility and=20 I'm fine with even disallowing it before those issues are resolved. Thanks Kevin 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 smtp3.osuosl.org (smtp3.osuosl.org [140.211.166.136]) (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 2A234C433EF for ; Fri, 18 Mar 2022 05:47:35 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by smtp3.osuosl.org (Postfix) with ESMTP id B48FF60B54; Fri, 18 Mar 2022 05:47:34 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp3.osuosl.org ([127.0.0.1]) by localhost (smtp3.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id q0nw9fvx5XPR; Fri, 18 Mar 2022 05:47:33 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [IPv6:2605:bc80:3010:104::8cd3:938]) by smtp3.osuosl.org (Postfix) with ESMTPS id 8788D60B29; Fri, 18 Mar 2022 05:47:33 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 4F2E7C0033; 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charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" > From: Jason Gunthorpe > Sent: Thursday, March 17, 2022 8:04 AM > > On Wed, Mar 16, 2022 at 10:23:26PM +0000, Luck, Tony wrote: > > > Kernel users (ring0) can supply any PASID when they use > > the ENQCMDS instruction. Is that what you mean when you > > say "real applications"? > > I'm not talking about ENQCMD at all > > I'm saying I don't see much utility to have two PASIDs assigned to the > same device that perform the same IOVA translation. > > So I would expect the list of attachments in an iommu_domain to have > exactly one device in it and multiple PASIDs to the same device from > the same iommu_domain is a oddball corner case we don't need to > optimize for, beyond being able to allow it to happen. > In theory we do have one example with SIOV. Say two mdev's of a same parent device are assigned to a guest and each mdev gets a unique PASID to tag the vRID requests. Then the guest attaches both mdev's to a stage-1 IOVA domain via vIOMMU, e.g. when it further assigns them to an user application. In this case the host iommu_domain wrapping the stage-1 page table is attached by two PASIDs of the same device. However iirc there are other tricky issues blocking this usage (Jacob may remember more detail here) and we didn't hear strong interest from customer on it. So this is just FYI for theoretical possibility and I'm fine with even disallowing it before those issues are resolved. Thanks Kevin _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu