From patchwork Mon Feb 17 10:18:21 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Teddy Astie X-Patchwork-Id: 13977472 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.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 C7F4AC021A1 for ; Mon, 17 Feb 2025 10:18:37 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.890003.1299041 (Exim 4.92) (envelope-from ) id 1tjyCn-0000Js-7G; Mon, 17 Feb 2025 10:18:25 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 890003.1299041; Mon, 17 Feb 2025 10:18:25 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1tjyCn-0000HP-2e; Mon, 17 Feb 2025 10:18:25 +0000 Received: by outflank-mailman (input) for mailman id 890003; Mon, 17 Feb 2025 10:18:24 +0000 Received: from se1-gles-flk1-in.inumbo.com ([94.247.172.50] helo=se1-gles-flk1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1tjyCm-0007sm-59 for xen-devel@lists.xenproject.org; Mon, 17 Feb 2025 10:18:24 +0000 Received: from mail178-27.suw51.mandrillapp.com (mail178-27.suw51.mandrillapp.com [198.2.178.27]) by se1-gles-flk1.inumbo.com (Halon) with ESMTPS id 835f7ba5-ed18-11ef-9896-31a8f345e629; Mon, 17 Feb 2025 11:18:21 +0100 (CET) Received: from pmta13.mandrill.prod.suw01.rsglab.com (localhost [127.0.0.1]) by mail178-27.suw51.mandrillapp.com (Mailchimp) with ESMTP id 4YxJWx1wGFz6CSstF for ; Mon, 17 Feb 2025 10:18:21 +0000 (GMT) Received: from [37.26.189.201] by mandrillapp.com id 20bbf2969e814bab919bb8bbf7cff5ee; Mon, 17 Feb 2025 10:18:21 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 835f7ba5-ed18-11ef-9896-31a8f345e629 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mandrillapp.com; s=mte1; t=1739787501; x=1740057501; bh=/PHfFCbkhgewAMWb/3Oro9AHwZl2KWijE79mLerB77A=; h=From:Subject:To:Cc:Message-Id:In-Reply-To:References:Feedback-ID: Date:MIME-Version:Content-Type:Content-Transfer-Encoding:CC:Date: Subject:From; b=Gp+3+rscyaRz66gfi/zO872Bcr/YgmjpwZwzZMOkb6m1IXCIttyF5ur0N7E2v3j6K 0oG8bVlxW857Vgb7L/8H2UTRLFRKU7a32r769nH51GSCV2In9Y3Rz0p14fzlq94dXZ SRITZI7Xiub5cdQYPBAqi5+O5RzC3mjVEtvULBjktJgvxHitb7joUFxka+OCu+KzsN EoXUA6yARHLxsEdbFtp+3/TUHBfB9k8GVUTZC92WIDqSWome+r/lVvwGBxMifAs1wX aX9l2JkVcEQoFwh+e8jHommyqZZKd9K/x3Ia0kZKZEQyZJM0qCV5w1hLaz4fi7GoPD g68RKIrjpy6vg== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=vates.tech; s=mte1; t=1739787501; x=1740048001; i=teddy.astie@vates.tech; bh=/PHfFCbkhgewAMWb/3Oro9AHwZl2KWijE79mLerB77A=; h=From:Subject:To:Cc:Message-Id:In-Reply-To:References:Feedback-ID: Date:MIME-Version:Content-Type:Content-Transfer-Encoding:CC:Date: Subject:From; b=Xd/q5q5Z9ranuo4FSO1oWWLFZhDc5is3RzZ+d08IqgYJGNkspl1EawLXqJWGcNAC3 e3vgNnOfImGgfuUdjmOTj5VzF2MEZte1J5Q7aHFZZ4KlO+bKk02TQUV4QwDQrxzp8B /2pghenlaZBFuSSV2biN65mX+SOYmbAznVPClLv9hN3AdKUYI5/vIiBz6xVh84364G h210CQz5YNZ+tpEDVA+qBgW4qOhyYNHipLduZKe5df4Ge/aP+ceaueaR7Vny4hj2R4 OScG/BW/RbqFqjTP0An2tBiC8w6Z56pWsAhS4I3DAXRFat7urz1Irk4tdlFKuR3dh2 BmocShdCYrrmg== From: "Teddy Astie" Subject: =?utf-8?q?=5BXEN_RFC_PATCH_v6_02/11=5D_docs/designs=3A_Add_a_design?= =?utf-8?q?_document_for_PV-IOMMU?= X-Mailer: git-send-email 2.47.2 X-Bm-Disclaimer: Yes X-Bm-Milter-Handled: 4ffbd6c1-ee69-4e1b-aabd-f977039bd3e2 X-Bm-Transport-Timestamp: 1739787499836 To: xen-devel@lists.xenproject.org Cc: "Teddy Astie" , "Andrew Cooper" , "Anthony PERARD" , "Michal Orzel" , "Jan Beulich" , "Julien Grall" , " =?utf-8?q?Roger_Pau_Monn=C3=A9?= " , "Stefano Stabellini" Message-Id: In-Reply-To: References: X-Native-Encoded: 1 X-Report-Abuse: =?utf-8?q?Please_forward_a_copy_of_this_message=2C_including?= =?utf-8?q?_all_headers=2C_to_abuse=40mandrill=2Ecom=2E_You_can_also_report_?= =?utf-8?q?abuse_here=3A_https=3A//mandrillapp=2Ecom/contact/abuse=3Fid=3D30?= =?utf-8?q?504962=2E20bbf2969e814bab919bb8bbf7cff5ee?= X-Mandrill-User: md_30504962 Feedback-ID: 30504962:30504962.20250217:md Date: Mon, 17 Feb 2025 10:18:21 +0000 MIME-Version: 1.0 Some operating systems want to use IOMMU to implement various features (e.g VFIO) or DMA protection. This patch introduce a proposal for IOMMU paravirtualization for Dom0. Signed-off-by: Teddy Astie --- docs/designs/pv-iommu.md | 116 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 116 insertions(+) create mode 100644 docs/designs/pv-iommu.md diff --git a/docs/designs/pv-iommu.md b/docs/designs/pv-iommu.md new file mode 100644 index 0000000000..7df9fa0b94 --- /dev/null +++ b/docs/designs/pv-iommu.md @@ -0,0 +1,116 @@ +# IOMMU paravirtualization for Dom0 + +Status: Experimental + +# Background + +By default, Xen only uses the IOMMU for itself, either to make device adress +space coherent with guest adress space (x86 HVM/PVH) or to prevent devices +from doing DMA outside it's expected memory regions including the hypervisor +(x86 PV). + +A limitation is that guests (especially privildged ones) may want to use +IOMMU hardware in order to implement features such as DMA protection and +VFIO [1] as IOMMU functionality is not available outside of the hypervisor +currently. + +[1] VFIO - "Virtual Function I/O" - https://www.kernel.org/doc/html/latest/driver-api/vfio.html + +# Design + +The operating system may want to have access to various IOMMU features such as +context management and DMA remapping. We can create a new hypercall that allows +the guest to have access to a new paravirtualized IOMMU interface. + +This feature is only meant to be available for the Dom0, as DomU have some +emulated devices that can't be managed on Xen side and are not hardware, we +can't rely on the hardware IOMMU to enforce DMA remapping. + +This interface is exposed under the `iommu_op` hypercall. + +In addition, Xen domains are modified in order to allow existence of several +IOMMU context including a default one that implement default behavior (e.g +hardware assisted paging) and can't be modified by guest. DomU cannot have +contexts, and therefore act as if they only have the default domain. + +Each IOMMU context within a Xen domain is identified using a domain-specific +context number that is used in the Xen IOMMU subsystem and the hypercall +interface. + +The number of IOMMU context a domain is specified by either the toolstack or +the domain itself. + +# IOMMU operations + +## Initialize PV-IOMMU + +Initialize PV-IOMMU for the domain. +It can only be called once. + +## Alloc context + +Create a new IOMMU context for the guest and return the context number to the +guest. +Fail if the IOMMU context limit of the guest is reached. + +A flag can be specified to create a identity mapping. + +## Free context + +Destroy a IOMMU context created previously. +It is not possible to free the default context. + +Reattach context devices to default context if specified by the guest. + +Fail if there is a device in the context and reattach-to-default flag is not +specified. + +## Reattach device + +Reattach a device to another IOMMU context (including the default one). +The target IOMMU context number must be valid and the context allocated. + +The guest needs to specify a PCI SBDF of a device he has access to. + +## Map/unmap page + +Map/unmap a page on a context. +The guest needs to specify a gfn and target dfn to map. + +Refuse to create the mapping if one already exist for the same dfn. + +## Lookup page + +Get the gfn mapped by a specific dfn. + +## Remote command + +Make a PV-IOMMU operation on behalf of another domain. +Especially useful for implementing IOMMU emulation (e.g using QEMU) +or initializing PV-IOMMU with enforced limits. + +# Implementation considerations + +## Hypercall batching + +In order to prevent unneeded hypercalls and IOMMU flushing, it is advisable to +be able to batch some critical IOMMU operations (e.g map/unmap multiple pages). + +## Hardware without IOMMU support + +Operating system needs to be aware on PV-IOMMU capability, and whether it is +able to make contexts. However, some operating system may critically fail in +case they are able to make a new IOMMU context. Which is supposed to happen +if no IOMMU hardware is available. + +The hypercall interface needs a interface to advertise the ability to create +and manage IOMMU contexts including the amount of context the guest is able +to use. Using these informations, the Dom0 may decide whether to use or not +the PV-IOMMU interface. + +## Page pool for contexts + +In order to prevent unexpected starving on the hypervisor memory with a +buggy Dom0. We can preallocate the pages the contexts will use and make +map/unmap use these pages instead of allocating them dynamically. +