[RFC PATCH 1/2] vfio-mdev: Wire in a request handler for mdev parent

Eric Farman
2020-11-17T03:21:47Z

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 <farman@linux.ibm.com>
---
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
+ * @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 */
--
2.17.1