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=-16.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 9E689C433E6 for ; Tue, 9 Mar 2021 15:45:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 68F656527C for ; Tue, 9 Mar 2021 15:45:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231789AbhCIPpb (ORCPT ); Tue, 9 Mar 2021 10:45:31 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:21495 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231651AbhCIPpU (ORCPT ); Tue, 9 Mar 2021 10:45:20 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615304719; 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=Te+OQSjfv0vY3+sUjOA7y5iasOCiA3WZDlj3UlBzKPY=; b=U2RsqfB74tota3NF9joyp/sY8/wYl1JH2IFREYX1vN4sLpgvr3myPFKbOgCLrtWegPugNI IS9T3vrmu7vHfOZZH0nkboKEBF9BSC/gT4U6HNkx74aHCbMolAKVsRnrb7PmliHqMQJniv DeyNiu5xMcSLdwm/99GFb9JkPY4KExA= 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-598-MuAluCWHM1O_fwqQeQ4KXg-1; Tue, 09 Mar 2021 10:45:18 -0500 X-MC-Unique: MuAluCWHM1O_fwqQeQ4KXg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1D75510866A0; Tue, 9 Mar 2021 15:45:17 +0000 (UTC) Received: from x1.home.shazbot.org (ovpn-112-255.phx2.redhat.com [10.3.112.255]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7EEB75D9CD; Tue, 9 Mar 2021 15:45:13 +0000 (UTC) Date: Tue, 9 Mar 2021 08:45:13 -0700 From: Alex Williamson To: Jason Gunthorpe Cc: cohuck@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, peterx@redhat.com Subject: Re: [PATCH v1 07/14] vfio: Add a device notifier interface Message-ID: <20210309084513.51fd2a97@x1.home.shazbot.org> In-Reply-To: <20210309004627.GD4247@nvidia.com> References: <161523878883.3480.12103845207889888280.stgit@gimli.home> <161524010999.3480.14282676267275402685.stgit@gimli.home> <20210309004627.GD4247@nvidia.com> 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 10.5.11.14 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 8 Mar 2021 20:46:27 -0400 Jason Gunthorpe wrote: > On Mon, Mar 08, 2021 at 02:48:30PM -0700, Alex Williamson wrote: > > Using a vfio device, a notifier block can be registered to receive > > select device events. Notifiers can only be registered for contained > > devices, ie. they are available through a user context. Registration > > of a notifier increments the reference to that container context > > therefore notifiers must minimally respond to the release event by > > asynchronously removing notifiers. > > > > Signed-off-by: Alex Williamson > > drivers/vfio/Kconfig | 1 + > > drivers/vfio/vfio.c | 35 +++++++++++++++++++++++++++++++++++ > > include/linux/vfio.h | 9 +++++++++ > > 3 files changed, 45 insertions(+) > > > > diff --git a/drivers/vfio/Kconfig b/drivers/vfio/Kconfig > > index 90c0525b1e0c..9a67675c9b6c 100644 > > +++ b/drivers/vfio/Kconfig > > @@ -23,6 +23,7 @@ menuconfig VFIO > > tristate "VFIO Non-Privileged userspace driver framework" > > select IOMMU_API > > select VFIO_IOMMU_TYPE1 if (X86 || S390 || ARM || ARM64) > > + select SRCU > > help > > VFIO provides a framework for secure userspace device drivers. > > See Documentation/driver-api/vfio.rst for more details. > > diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c > > index c47895539a1a..7f6d00e54e83 100644 > > +++ b/drivers/vfio/vfio.c > > @@ -105,6 +105,7 @@ struct vfio_device { > > struct list_head group_next; > > void *device_data; > > struct inode *inode; > > + struct srcu_notifier_head notifier; > > }; > > > > #ifdef CONFIG_VFIO_NOIOMMU > > @@ -601,6 +602,7 @@ struct vfio_device *vfio_group_create_device(struct vfio_group *group, > > device->ops = ops; > > device->device_data = device_data; > > dev_set_drvdata(dev, device); > > + srcu_init_notifier_head(&device->notifier); > > > > /* No need to get group_lock, caller has group reference */ > > vfio_group_get(group); > > @@ -1785,6 +1787,39 @@ static const struct file_operations vfio_device_fops = { > > .mmap = vfio_device_fops_mmap, > > }; > > > > +int vfio_device_register_notifier(struct vfio_device *device, > > + struct notifier_block *nb) > > +{ > > + int ret; > > + > > + /* Container ref persists until unregister on success */ > > + ret = vfio_group_add_container_user(device->group); > > I'm having trouble guessing why we need to refcount the group to add a > notifier to the device's notifier chain? > > I suppose it actually has to do with the MMIO mapping? But I don't > know what the relation is between MMIO mappings in the IOMMU and the > container? This could deserve a comment? Sure, I can add a comment. We want to make sure the device remains within an IOMMU context so long as we have a DMA mapping to the device MMIO, which could potentially manipulate the device. IOMMU context is managed a the group level. > > +void vfio_device_unregister_notifier(struct vfio_device *device, > > + struct notifier_block *nb) > > +{ > > + if (!srcu_notifier_chain_unregister(&device->notifier, nb)) > > + vfio_group_try_dissolve_container(device->group); > > +} > > +EXPORT_SYMBOL_GPL(vfio_device_unregister_notifier); > > Is the SRCU still needed with the new locking? With a cursory look I > only noticed this called under the reflck->lock ? When registering the notifier, the iommu->lock is held. During the callback, the same lock is acquired, so we'd have AB-BA otherwise. Thanks, Alex