Re: [PATCH v1 02/18] vfio/ccw: Fix FSM state if mdev probe fails

Eric Farman
2022-06-03T19:12:31Z

On Fri, 2022-06-03 at 09:21 -0400, Matthew Rosato wrote:
> On 6/2/22 1:19 PM, Eric Farman wrote:
> > The FSM is in STANDBY state when arriving in vfio_ccw_mdev_probe(),
> > and this routine converts it to IDLE as part of its processing.
> > The error exit sets it to IDLE (again) but clears the private->mdev
> > pointer.
> >
> > The FSM should of course be managing the state itself, but the
> > correct thing for vfio_ccw_mdev_probe() to do would be to put
> > the state back the way it found it.
> >
> > The corresponding check of private->mdev in vfio_ccw_sch_io_todo()
> > can be removed, since the distinction is unnecessary at this point.
> >
> > Fixes: 3bf1311f351ef ("vfio/ccw: Convert to use
> > vfio_register_emulated_iommu_dev()")
> > Signed-off-by: Eric Farman <farman@linux.ibm.com>
> > ---
> > drivers/s390/cio/vfio_ccw_drv.c | 2 +-
> > drivers/s390/cio/vfio_ccw_ops.c | 2 +-
> > 2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/s390/cio/vfio_ccw_drv.c
> > b/drivers/s390/cio/vfio_ccw_drv.c
> > index 35055eb94115..b18b4582bc8b 100644
> > --- a/drivers/s390/cio/vfio_ccw_drv.c
> > +++ b/drivers/s390/cio/vfio_ccw_drv.c
> > @@ -108,7 +108,7 @@ static void vfio_ccw_sch_io_todo(struct
> > work_struct *work)
> > * has finished. Do not overwrite a possible processing
> > * state if the final interrupt was for HSCH or CSCH.
> > */
> > - if (private->mdev && cp_is_finished)
> > + if (cp_is_finished)
> > private->state = VFIO_CCW_STATE_IDLE;
>
> Took me a bit to convince myself this was OK

Me too. :)

> , mainly because AFAICT
> despite the change below the fsm jumptable would still allow you to
> reach this code when in STANDBY. But, it should only be possible for
> an
> unsolicited interrupt (e.g. unsolicited implies !cp_is_finished) so
> we
> would still avoid a STANDBY->IDLE transition on accident.
>
> Maybe work unsolicited interrupt into the comment block above along
> with
> HSCH/CSCH?

Good idea. How about:

/*
* Reset to IDLE only if
processing of a channel program
* has finished. Do not
overwrite a possible processing
* state if the interrupt was
unsolicited, or if the final
* interrupt was for HSCH or CSCH.

*/

>
> Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
>
> >
> > if (private->io_trigger)
> > diff --git a/drivers/s390/cio/vfio_ccw_ops.c
> > b/drivers/s390/cio/vfio_ccw_ops.c
> > index bebae21228aa..a403d059a4e6 100644
> > --- a/drivers/s390/cio/vfio_ccw_ops.c
> > +++ b/drivers/s390/cio/vfio_ccw_ops.c
> > @@ -146,7 +146,7 @@ static int vfio_ccw_mdev_probe(struct
> > mdev_device *mdev)
> > vfio_uninit_group_dev(&private->vdev);
> > atomic_inc(&private->avail);
> > private->mdev = NULL;
> > - private->state = VFIO_CCW_STATE_IDLE;
> > + private->state = VFIO_CCW_STATE_STANDBY;