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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 2B252C433DF for ; Fri, 15 May 2020 18:26:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EEB3520671 for ; Fri, 15 May 2020 18:26:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726257AbgEOS0E (ORCPT ); Fri, 15 May 2020 14:26:04 -0400 Received: from mx2.suse.de ([195.135.220.15]:46810 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726206AbgEOS0D (ORCPT ); Fri, 15 May 2020 14:26:03 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id C0E6FAD93; Fri, 15 May 2020 18:26:04 +0000 (UTC) Date: Fri, 15 May 2020 20:26:00 +0200 From: Joerg Roedel To: Robin Murphy Cc: Joerg Roedel , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Tom Murphy , jsnitsel@redhat.com Subject: Re: [PATCH] iommu: Implement deferred domain attachment Message-ID: <20200515182600.GJ8135@suse.de> References: <20200515094519.20338-1-joro@8bytes.org> <20200515161400.GZ18353@8bytes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 15, 2020 at 05:28:53PM +0100, Robin Murphy wrote: > On 2020-05-15 17:14, Joerg Roedel wrote: > > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c > > index ba128d1cdaee..403fda04ea98 100644 > > --- a/drivers/iommu/dma-iommu.c > > +++ b/drivers/iommu/dma-iommu.c > > @@ -362,8 +362,8 @@ static int iommu_dma_deferred_attach(struct device *dev, > > return 0; > > if (unlikely(ops->is_attach_deferred && > > - ops->is_attach_deferred(domain, dev))) > > - return iommu_attach_device(domain, dev); > > + ops->is_attach_deferred(domain, dev))) > > + return iommu_attach_device_no_defer(domain, dev); > > Wouldn't it be simpler to just invoke ops->attach_dev directly and avoid > having to formalise a public interface that nobody else should ever use > anyway? That would omit the ops->attach_dev != NULL check and the trace-point on device attach. Besides that, it would be a layering violation. But the function is of course entirely internal to the iommu subsytem and is a good canditate to be moved to a header file in drivers/iommu. > @@ -746,8 +747,11 @@ int iommu_group_add_device(struct iommu_group *group, > struct device *dev) > > mutex_lock(&group->mutex); > list_add_tail(&device->list, &group->devices); > - if (group->domain) > - ret = __iommu_attach_device(group->domain, dev); > + domain = group->domain; > + if (domain && (!domain->ops->is_attach_deferred || > + !domain->ops->is_attach_deferred(domain, dev))) > + ret = __iommu_attach_device(domain, dev); > + } > mutex_unlock(&group->mutex); > if (ret) > goto err_put_group; No, doing this in iommu_group_add_device() doesn't solve the problem. The attach must not happen before a device driver took control of the device and silenced any DMA initiated by the old kernel. At probe time this isn't guaranteed. Joerg