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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_MUTT 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 48BA3C10F00 for ; Mon, 25 Feb 2019 14:22:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 205732146F for ; Mon, 25 Feb 2019 14:22:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727324AbfBYOWU (ORCPT ); Mon, 25 Feb 2019 09:22:20 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:33108 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726313AbfBYOWT (ORCPT ); Mon, 25 Feb 2019 09:22:19 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id CBF8780D; Mon, 25 Feb 2019 06:22:18 -0800 (PST) Received: from debian (c02th0x6hf1t.nice.arm.com [10.36.160.142]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B6CA33F575; Mon, 25 Feb 2019 06:22:14 -0800 (PST) Date: Mon, 25 Feb 2019 15:22:10 +0100 From: Vincent =?utf-8?Q?Stehl=C3=A9?= To: Eric Auger Cc: eric.auger.pro@gmail.com, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, joro@8bytes.org, alex.williamson@redhat.com, jacob.jun.pan@linux.intel.com, yi.l.liu@linux.intel.com, jean-philippe.brucker@arm.com, will.deacon@arm.com, robin.murphy@arm.com, kevin.tian@intel.com, ashok.raj@intel.com, marc.zyngier@arm.com, christoffer.dall@arm.com, peter.maydell@linaro.org Subject: Re: [PATCH v4 19/22] vfio-pci: Register an iommu fault handler Message-ID: <20190225142209.GC23257@debian> References: <20190218135504.25048-1-eric.auger@redhat.com> <20190218135504.25048-20-eric.auger@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190218135504.25048-20-eric.auger@redhat.com> 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 Hi Eric, On Mon, Feb 18, 2019 at 02:55:00PM +0100, Eric Auger wrote: > This patch registers a fault handler which records faults in > a circular buffer and then signals an eventfd. This buffer is > exposed within the fault region. > > Signed-off-by: Eric Auger > --- > drivers/vfio/pci/vfio_pci.c | 49 +++++++++++++++++++++++++++++ > drivers/vfio/pci/vfio_pci_private.h | 1 + > 2 files changed, 50 insertions(+) > > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c > index aaf63e5ca2b6..019c9fd380a5 100644 > --- a/drivers/vfio/pci/vfio_pci.c > +++ b/drivers/vfio/pci/vfio_pci.c (..) > static int vfio_pci_init_fault_region(struct vfio_pci_device *vdev) > { > struct vfio_region_fault_prod *header; > @@ -276,6 +317,13 @@ static int vfio_pci_init_fault_region(struct vfio_pci_device *vdev) > header = (struct vfio_region_fault_prod *)vdev->fault_pages; > header->version = -1; > header->offset = PAGE_SIZE; > + > + ret = iommu_register_device_fault_handler(&vdev->pdev->dev, > + vfio_pci_iommu_dev_fault_handler, > + vdev); > + if (ret) > + goto out; > + > return 0; > out: > kfree(vdev->fault_pages); This patch calls iommu_register_device_fault_handler from vfio_pci_init_fault_region, leading to the following call stack: iommu_register_device_fault_handler vfio_pci_init_fault_region vfio_pci_enable vfio_pci_open vfio_group_get_device_fd > @@ -1420,6 +1468,7 @@ static void vfio_pci_remove(struct pci_dev *pdev) > vfio_iommu_group_put(pdev->dev.iommu_group, &pdev->dev); > kfree(vdev->region); > kfree(vdev->fault_pages); > + iommu_unregister_device_fault_handler(&pdev->dev); > mutex_destroy(&vdev->ioeventfds_lock); > kfree(vdev); And then this patch calls iommu_unregister_device_fault_handler from vfio_pci_remove, and not from vfio_pci_release. I think this means a device cannot be used twice in a row without unloading the module. Here is an example sequence: 1. modprobe vfio-pci 2. Userspace uses VFIO, calls ioctl(VFIO_GROUP_GET_DEVICE_FD) 2.1. iommu_register_device_fault_handler is called 3. Userspace exits 3.1. vfio_pci_release is called, but iommu_unregister_device_fault_handler is not called 4. Userspace uses VFIO agin, calls ioctl(VFIO_GROUP_GET_DEVICE_FD) again 4.1. iommu_register_device_fault_handler is called again, notices a fault handler is already there, returns -EBUSY Unloading the vfio-pci module will call vfio_pci_remove. Maybe iommu_unregister_device_fault_handler should be called from vfio_pci_release instead of vfio_pci_remove? Best regards, Vincent.