Re: [PATCH 06/12] vfio/ap_ops: Convert to use vfio_register_group_dev()

Cornelia Huck
2021-05-04T15:30:51Z

On Mon, 3 May 2021 16:14:43 -0400
Tony Krowiak <akrowiak@linux.ibm.com> wrote:

> On 4/26/21 1:48 PM, Cornelia Huck wrote:
> > On Fri, 23 Apr 2021 20:03:03 -0300
> > Jason Gunthorpe <jgg@nvidia.com> wrote:
> >
> >> This is straightforward conversion, the ap_matrix_mdev is actually serving
> >> as the vfio_device and we can replace all the mdev_get_drvdata()'s with a
> >> simple container_of().
> >>
> >> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> >> ---
> >> drivers/s390/crypto/vfio_ap_ops.c | 137 ++++++++++++++++----------
> >> drivers/s390/crypto/vfio_ap_private.h | 2 +
> >> 2 files changed, 89 insertions(+), 50 deletions(-)
> >>
> > (...)
> >
> >> -static int vfio_ap_mdev_remove(struct mdev_device *mdev)
> >> +static void vfio_ap_mdev_remove(struct mdev_device *mdev)
> >> {
> >> - struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
> >> + struct ap_matrix_mdev *matrix_mdev = dev_get_drvdata(&mdev->dev);
> >>
> >> - if (matrix_mdev->kvm)
> >> - return -EBUSY;
> >> + /* FIXME: Remove isn't allowed to fail */
> >> + if (WARN_ON(matrix_mdev->kvm))
> >> + return;
> > This is a pre-existing problem, but the rework now makes it more
> > obvious.
>
> I agree, I was not aware that returning a non-zero return code
> from this callback did not return the -EBUSY to userspace
> when the mdev is removed.
>
> >
> > Previously, the mdev code would only print a warning and then continue
> > with device removal, even if a ->remove() callback returned an error.
> > Now, it's quite clear that we'll end up in a weird half-dead state.
>
> With the latest kernel from our tree, the remove hangs until the
> guest is shutdown and the mdev fd is closed. During the hang, the
> dmesg log has the following:
>
> "No mdev vendor driver request callback support, blocked until released
> by user"
>
> So, it looks like nothing is done with the mdev until the fd for the
> mdev is closed when the guest is shut down, at which time the
> mdev is removed.

You probably want to wire up the request callback and notify userspace.

What happens today if the device in QEMU is removed via device_del?
Does that already clean up things properly?