Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934679AbbGVQyi (ORCPT ); Wed, 22 Jul 2015 12:54:38 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44616 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934598AbbGVQyg (ORCPT ); Wed, 22 Jul 2015 12:54:36 -0400 Message-ID: <1437584075.5211.34.camel@redhat.com> Subject: Re: [RFC PATCH 1/1] vfio-pci/iommu: Detach iommu group on remove path From: Alex Williamson To: Gerald Schaefer Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Martin Schwidefsky , Sebastian Ott Date: Wed, 22 Jul 2015 10:54:35 -0600 In-Reply-To: <1437500646-18031-2-git-send-email-gerald.schaefer@de.ibm.com> References: <1437500646-18031-1-git-send-email-gerald.schaefer@de.ibm.com> <1437500646-18031-2-git-send-email-gerald.schaefer@de.ibm.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2416 Lines: 59 On Tue, 2015-07-21 at 19:44 +0200, Gerald Schaefer wrote: > When a user completes the VFIO_SET_IOMMU ioctl and the vfio-pci device is > removed thereafter (before any other ioctl like VFIO_GROUP_GET_DEVICE_FD), > then the detach_dev callback of the underlying IOMMU API is never called. > > This patch adds a call to vfio_group_try_dissolve_container() to the remove > path, which will trigger the missing detach_dev callback in this scenario. > > Signed-off-by: Gerald Schaefer > --- > drivers/vfio/vfio.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c > index 2fb29df..9c5c784 100644 > --- a/drivers/vfio/vfio.c > +++ b/drivers/vfio/vfio.c > @@ -711,6 +711,8 @@ static bool vfio_dev_present(struct vfio_group *group, struct device *dev) > return true; > } > > +static void vfio_group_try_dissolve_container(struct vfio_group *group); > + > /* > * Decrement the device reference count and wait for the device to be > * removed. Open file descriptors for the device... */ > @@ -785,6 +787,7 @@ void *vfio_del_group_dev(struct device *dev) > } > } while (ret <= 0); > > + vfio_group_try_dissolve_container(group); > vfio_group_put(group); > > return device_data; This won't work, vfio_group_try_dissolve_container() decrements container_users, which an unused device is not. Imagine if we had more than one device in the iommu group, one device is removed and the container is dissolved despite the user holding a reference and other viable devices remaining. Additionally, from an isolation perspective, an unbind from vfio-pci should not pull the device out of the iommu domain, it's part of the domain because it's not isolated and that continues even after unbind. I think what you want to do is detach a device from the iommu domain only when it's being removed from iommu group, such as through iommu_group_remove_device(). We already have a bit of an asymmetry there as iommu_group_add_device() will add devices to the currently active iommu domain for the group, but iommu_group_remove_device() does not appear to do the reverse. Thanks, Alex -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/