From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:43324 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726977AbgLCDEh (ORCPT ); Wed, 2 Dec 2020 22:04:37 -0500 Subject: Re: [PATCH v2 1/2] vfio-mdev: Wire in a request handler for mdev parent References: <20201120180740.87837-1-farman@linux.ibm.com> <20201120180740.87837-2-farman@linux.ibm.com> <20201202132838.6a872c17@w520.home> From: Eric Farman Message-ID: Date: Wed, 2 Dec 2020 22:02:36 -0500 MIME-Version: 1.0 In-Reply-To: <20201202132838.6a872c17@w520.home> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit List-ID: To: Alex Williamson Cc: Cornelia Huck , Kirti Wankhede , Halil Pasic , Matthew Rosato , linux-s390@vger.kernel.org, kvm@vger.kernel.org On 12/2/20 3:28 PM, Alex Williamson wrote: > On Fri, 20 Nov 2020 19:07:39 +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 >> device being physically removed from the host can be (gracefully?) >> handled by the parent device at the time the device is removed. >> >> Add a message when registering the device if a driver doesn't >> provide this callback, so a clue is given that this same loop >> may be encountered in a similar situation. >> >> Signed-off-by: Eric Farman >> --- >> drivers/vfio/mdev/mdev_core.c | 4 ++++ >> drivers/vfio/mdev/vfio_mdev.c | 10 ++++++++++ >> include/linux/mdev.h | 4 ++++ >> 3 files changed, 18 insertions(+) >> >> diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c >> index b558d4cfd082..6de97d25a3f8 100644 >> --- a/drivers/vfio/mdev/mdev_core.c >> +++ b/drivers/vfio/mdev/mdev_core.c >> @@ -154,6 +154,10 @@ int mdev_register_device(struct device *dev, const struct mdev_parent_ops *ops) >> if (!dev) >> return -EINVAL; >> >> + /* Not mandatory, but its absence could be a problem */ >> + if (!ops->request) >> + dev_info(dev, "Driver cannot be asked to release device\n"); >> + >> mutex_lock(&parent_list_lock); >> >> /* Check for duplicate */ >> diff --git a/drivers/vfio/mdev/vfio_mdev.c b/drivers/vfio/mdev/vfio_mdev.c >> index 30964a4e0a28..06d8fc4a6d72 100644 >> --- a/drivers/vfio/mdev/vfio_mdev.c >> +++ b/drivers/vfio/mdev/vfio_mdev.c >> @@ -98,6 +98,15 @@ 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 (parent->ops->request) >> + parent->ops->request(mdev, count); > > What do you think about duplicating the count==0 notice in the else > case here? ie. > > else if (count == 0) > dev_notice(mdev_dev(mdev), "No mdev vendor driver request callback support, blocked until released by user\n"); > I'm fine with that. If there are no objections, I should be able to spin a v3 with such a change tomorrow. Thank you! Eric > This at least puts something in the log a bit closer to the timeframe > of a possible issue versus the registration nag. vfio-core could do > this too, but vfio-mdev registers a request callback on behalf of all > mdev devices, so vfio-core would no longer have visibility for this > case. > > Otherwise this series looks fine to me and I can take it through the > vfio tree. Thanks, > > Alex > >> +} >> + >> static const struct vfio_device_ops vfio_mdev_dev_ops = { >> .name = "vfio-mdev", >> .open = vfio_mdev_open, >> @@ -106,6 +115,7 @@ 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..9004375c462e 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 to release device >> + * @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 */ >