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 62482C433E0 for ; Wed, 8 Jul 2020 19:07:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4343620674 for ; Wed, 8 Jul 2020 19:07:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="EV0Se9Jr" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726139AbgGHTH4 (ORCPT ); Wed, 8 Jul 2020 15:07:56 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:38554 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726044AbgGHTH4 (ORCPT ); Wed, 8 Jul 2020 15:07:56 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1594235274; 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=i2jzZdLUrEZwSvsltld7qJazxhy6bdHEH3AcJYhJaq4=; b=EV0Se9JrMwMpQ68jPqaDD3EovI0m7+ilcKw59QJfZNbrimv12l1C4+ZRUfiOy9emPiyVWU ygrd8ZP4GGqtW63pYXbgkRd3mQe8UApkJThh0CgHOl202wCPDsti0ArdBZyRLuGt0EnKqN ASYAYe1BtCMtgJqhF1+CF1hiUNuHXK4= 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-85-XdLsMZw-McaWOVhxfaNBeA-1; Wed, 08 Jul 2020 15:07:52 -0400 X-MC-Unique: XdLsMZw-McaWOVhxfaNBeA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9ED62800C64; Wed, 8 Jul 2020 19:07:50 +0000 (UTC) Received: from x1.home (ovpn-112-71.phx2.redhat.com [10.3.112.71]) by smtp.corp.redhat.com (Postfix) with ESMTP id AF58773FEA; Wed, 8 Jul 2020 19:07:49 +0000 (UTC) Date: Wed, 8 Jul 2020 13:07:49 -0600 From: Alex Williamson To: Lu Baolu Cc: Joerg Roedel , Robin Murphy , Cornelia Huck , Kevin Tian , Ashok Raj , Dave Jiang , Liu Yi L , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH v2 1/2] iommu: iommu_aux_at(de)tach_device() extension Message-ID: <20200708130749.1b1e1421@x1.home> In-Reply-To: References: <20200707013957.23672-1-baolu.lu@linux.intel.com> <20200707013957.23672-2-baolu.lu@linux.intel.com> <20200707150408.474d81f1@x1.home> Organization: Red Hat MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, 8 Jul 2020 10:53:12 +0800 Lu Baolu wrote: > Hi Alex, > > Thanks a lot for your comments. Please check my reply inline. > > On 7/8/20 5:04 AM, Alex Williamson wrote: > > On Tue, 7 Jul 2020 09:39:56 +0800 > > Lu Baolu wrote: > > > >> The hardware assistant vfio mediated device is a use case of iommu > >> aux-domain. The interactions between vfio/mdev and iommu during mdev > >> creation and passthr are: > >> > >> - Create a group for mdev with iommu_group_alloc(); > >> - Add the device to the group with > >> group = iommu_group_alloc(); > >> if (IS_ERR(group)) > >> return PTR_ERR(group); > >> > >> ret = iommu_group_add_device(group, &mdev->dev); > >> if (!ret) > >> dev_info(&mdev->dev, "MDEV: group_id = %d\n", > >> iommu_group_id(group)); > >> - Allocate an aux-domain > >> iommu_domain_alloc() > >> - Attach the aux-domain to the physical device from which the mdev is > >> created. > >> iommu_aux_attach_device() > >> > >> In the whole process, an iommu group was allocated for the mdev and an > >> iommu domain was attached to the group, but the group->domain leaves > >> NULL. As the result, iommu_get_domain_for_dev() doesn't work anymore. > >> > >> The iommu_get_domain_for_dev() is a necessary interface for device > >> drivers that want to support aux-domain. For example, > >> > >> struct iommu_domain *domain; > >> struct device *dev = mdev_dev(mdev); > >> unsigned long pasid; > >> > >> domain = iommu_get_domain_for_dev(dev); > >> if (!domain) > >> return -ENODEV; > >> > >> pasid = iommu_aux_get_pasid(domain, dev->parent); > > How did we know this was an aux domain? ie. How did we know we could > > use it with iommu_aux_get_pasid()? > > Yes. It's a bit confusing if iommu_get_domain_for_dev() is reused here > for aux-domain. > > > > > Why did we assume the parent device is the iommu device for the aux > > domain? Should that level of detail be already known by the aux domain? > > > > Nits - The iomu device of an mdev device is found via > > mdev_get_iommu_device(dev), it should not be assumed to be the parent. > > The parent of an mdev device is found via mdev_parent_dev(mdev). > > My bad. The driver should use mdev_get_iommu_device() instead. > > > > > The leaps in logic here make me wonder if we should instead be exposing > > more of an aux domain API rather than blurring the differences between > > these domains. Thanks, > > How about add below API? > > /** > * iommu_aux_get_domain_for_dev - get aux domain for a device > * @dev: the accessory device > * > * The caller should pass a valid @dev to iommu_aux_attach_device() before > * calling this api. Return an attached aux-domain, or NULL otherwise. That's not necessarily the caller's responsibility, that might happen elsewhere, this function simply returns an aux domain for the device if it's attached to one. > */ > struct iommu_domain *iommu_aux_get_domain_for_dev(struct device *dev) > { > struct iommu_domain *domain = NULL; > struct iommu_group *group; > > group = iommu_group_get(dev); > if (!group) > return NULL; > > if (group->aux_domain_attached) > domain = group->domain; > > iommu_group_put(group); > > return domain; > } > EXPORT_SYMBOL_GPL(iommu_aux_get_domain_for_dev); For your example use case, this seems more clear to me. Thanks, Alex