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vfio-mdev: Wire in a request handler for mdev parent

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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, and a message when
this occurs instead of the awkward silence noted above.

Signed-off-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
This commit is contained in:
Eric Farman 2020-12-03 22:35:11 +01:00 committed by Alex Williamson
parent d22f9a6c92
commit a15ac665b9
3 changed files with 21 additions and 0 deletions
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4
drivers/vfio/mdev/mdev_core.c
View file

@ -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 */

13
drivers/vfio/mdev/vfio_mdev.c
View file

@ -98,6 +98,18 @@ 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);
else if (count == 0)
dev_notice(mdev_dev(mdev),
"No mdev vendor driver request callback support, blocked until released by user\n");
}
static const struct vfio_device_ops vfio_mdev_dev_ops = {
.name = "vfio-mdev",
.open = vfio_mdev_open,
@ -106,6 +118,7 @@ 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)

4
include/linux/mdev.h
View file

@ -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 */