From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:56633 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726495AbgKSLaj (ORCPT ); Thu, 19 Nov 2020 06:30:39 -0500 Date: Thu, 19 Nov 2020 12:30:26 +0100 From: Cornelia Huck Subject: Re: [RFC PATCH 1/2] vfio-mdev: Wire in a request handler for mdev parent Message-ID: <20201119123026.1353cb3c.cohuck@redhat.com> In-Reply-To: <20201117032139.50988-2-farman@linux.ibm.com> References: <20201117032139.50988-1-farman@linux.ibm.com> <20201117032139.50988-2-farman@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit List-ID: To: Eric Farman Cc: Kirti Wankhede , Alex Williamson , Halil Pasic , linux-s390@vger.kernel.org, kvm@vger.kernel.org On Tue, 17 Nov 2020 04:21:38 +0100 Eric Farman wrote: > While performing some destructive tests with vfio-ccw, where the > paths to a device are forcible removed and thus the device itself > is unreachable, it is rather easy to end up in an endless loop in > vfio_del_group_dev() due to the lack of a request callback for the > associated device. > > In this example, one MDEV (77c) is used by a guest, while another > (77b) is not. The symptom is that the iommu is detached from the > mdev for 77b, but not 77c, until that guest is shutdown: > > [ 238.794867] vfio_ccw 0.0.077b: MDEV: Unregistering > [ 238.794996] vfio_mdev 11f2d2bc-4083-431d-a023-eff72715c4f0: Removing from iommu group 2 > [ 238.795001] vfio_mdev 11f2d2bc-4083-431d-a023-eff72715c4f0: MDEV: detaching iommu > [ 238.795036] vfio_ccw 0.0.077c: MDEV: Unregistering > ...silence... > > Let's wire in the request call back to the mdev device, so that a hot > unplug can be (gracefully?) handled by the parent device at the time > the device is being removed. I think it makes a lot of sense to give the vendor driver a way to handle requests. > > Signed-off-by: Eric Farman > --- > drivers/vfio/mdev/vfio_mdev.c | 11 +++++++++++ > include/linux/mdev.h | 4 ++++ > 2 files changed, 15 insertions(+) > > diff --git a/drivers/vfio/mdev/vfio_mdev.c b/drivers/vfio/mdev/vfio_mdev.c > index 30964a4e0a28..2dd243f73945 100644 > --- a/drivers/vfio/mdev/vfio_mdev.c > +++ b/drivers/vfio/mdev/vfio_mdev.c > @@ -98,6 +98,16 @@ static int vfio_mdev_mmap(void *device_data, struct vm_area_struct *vma) > return parent->ops->mmap(mdev, vma); > } > > +static void vfio_mdev_request(void *device_data, unsigned int count) > +{ > + struct mdev_device *mdev = device_data; > + struct mdev_parent *parent = mdev->parent; > + > + if (unlikely(!parent->ops->request)) Hm. Do you think that all drivers should implement a ->request() callback? > + return; > + parent->ops->request(mdev, count); > +} > + > static const struct vfio_device_ops vfio_mdev_dev_ops = { > .name = "vfio-mdev", > .open = vfio_mdev_open,