On Fri, 20 Nov 2020 19:07:39 +0100 Eric Farman <farman@xxxxxxxxxxxxx> 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 <farman@xxxxxxxxxxxxx> > --- > drivers/vfio/mdev/mdev_core.c | 4 ++++ > drivers/vfio/mdev/vfio_mdev.c | 10 ++++++++++ > include/linux/mdev.h | 4 ++++ > 3 files changed, 18 insertions(+) Reviewed-by: Cornelia Huck <cohuck@xxxxxxxxxx>
