From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:7934 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728360AbgKSPaN (ORCPT ); Thu, 19 Nov 2020 10:30:13 -0500 Date: Thu, 19 Nov 2020 16:29:58 +0100 From: Halil Pasic Subject: Re: [RFC PATCH 1/2] vfio-mdev: Wire in a request handler for mdev parent Message-ID: <20201119162958.2c1a0781.pasic@linux.ibm.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: 8bit List-ID: To: Eric Farman Cc: Cornelia Huck , Kirti Wankhede , Alex Williamson , 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. > > 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)) > + return; > + parent->ops->request(mdev, count); > +} > + > static const struct vfio_device_ops vfio_mdev_dev_ops = { > .name = "vfio-mdev", > .open = vfio_mdev_open, > @@ -106,6 +116,7 @@ static const struct vfio_device_ops vfio_mdev_dev_ops = { > .read = vfio_mdev_read, > .write = vfio_mdev_write, > .mmap = vfio_mdev_mmap, > + .request = vfio_mdev_request, > }; > > static int vfio_mdev_probe(struct device *dev) > diff --git a/include/linux/mdev.h b/include/linux/mdev.h > index 0ce30ca78db0..0ed88be1f4bb 100644 > --- a/include/linux/mdev.h > +++ b/include/linux/mdev.h > @@ -72,6 +72,9 @@ struct device *mdev_get_iommu_device(struct device *dev); > * @mmap: mmap callback > * @mdev: mediated device structure > * @vma: vma structure > + * @request: request callback In include/linux/vfio.h it is documented like * @request: Request for the bus driver to release the device Can we add 'to release' here as well? IMHO, when one requests, one needs to say what is requested. So I would expect a function called request() to have a parameter (direct or indirect) that expresses, what is requested. But this does not seem to be the case here. Or did I miss it? Well it's called request() and not request_removal() in vfio, so I believe it's only consistent to keep calling it request(). But I do think we should at least document what is actually requested. Otherwise LGTM! > + * @mdev: mediated device structure > + * @count: request sequence number > * Parent device that support mediated device should be registered with mdev > * module with mdev_parent_ops structure. > **/ > @@ -92,6 +95,7 @@ struct mdev_parent_ops { > long (*ioctl)(struct mdev_device *mdev, unsigned int cmd, > unsigned long arg); > int (*mmap)(struct mdev_device *mdev, struct vm_area_struct *vma); > + void (*request)(struct mdev_device *mdev, unsigned int count); > }; > > /* interface for exporting mdev supported type attributes */