Re: [PATCH v7 11/15] s390/vfio-ap: Transition device migration state to STOP

[Anthony Krowiak]

On 8/20/26 8:43 AM, Jason J. Herne wrote:
> On 8/7/26 6:18 PM, Anthony Krowiak wrote:
> > Typically at this point, interrupt processing for the device, DMA and 
> > other
> > changes to the device's external state must be prohibited. For VFIO AP,
> > there is no physical DMA device virtualized by the vfio-ap device . It
> > merely manages the guest's AP configuration that identifies the devices
> > passed through to the guest, but does not have access to any of them. 
> > Those
> > AP devices are passed through and controlled exclusively by the SIE 
> > program
>
> SIE is an instruction, not a program. It might be clearer to say:
> pass-through AP devices are controlled by the hardware.

The SIE control block is used to pass through the AP devices via the 
CRYCB which
I assume is processed by the SIE instruction. After that, vfio_ap has 
nothing to do
with the AP devices other than to handle interrupt enable/disable when the
PQAP(AQIC) instruction is intercepted. The vfio_ap driver does not 
manage I/O
between the guest and device memory like other devices using VFIO to 
pass them
through. It's sole purpose in life is to manage the AP configuration for 
the guest
to which an mdev is attached.

I'll make a change to this comment.

> I'm not sure there is much benefit to having this as a separate patch 
> at all. You could simply roll this into the patch where this logic is 
> originally constructed and skip this patch entirely.

Already addressed with response to 12/15 review comment you made.

> > used to start the guest. There  only thing to do at this point is return
> > NULL to the caller since the file streams and associated data will get
> > cleaned up as a result of the VFIO migration framework releasing the 
> > files.
> >
> > Signed-off-by: Anthony Krowiak <akrowiak@xxxxxxxxxxxxx>
> > ---
> >   drivers/s390/crypto/vfio_ap_migration.c | 9 +++++++--
> >   1 file changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/s390/crypto/vfio_ap_migration.c 
> > b/drivers/s390/crypto/vfio_ap_migration.c
> > index 4dd7373c3d9d..30160e3ddded 100644
> > --- a/drivers/s390/crypto/vfio_ap_migration.c
> > +++ b/drivers/s390/crypto/vfio_ap_migration.c
> > @@ -1511,12 +1511,17 @@ vfio_ap_transition_to_state(struct 
> > ap_matrix_mdev *matrix_mdev,
> >           return filp;
> >       }
> >   +    /*
> > +     * Terminates the data transfer session of the vfio-ap device state
> > +     * between the source and target hosts. Since the vfio-ap device 
> > does
> > +     * not virtualize a DMA device, there is no internal device 
> > state to
> > +     * incorporate into the vfio-ap device on the target.
> > +     */
> >       if ((cur_state == VFIO_DEVICE_STATE_RESUMING &&
> >            new_state == VFIO_DEVICE_STATE_STOP) ||
> >           (cur_state == VFIO_DEVICE_STATE_STOP_COPY &&
> >            new_state == VFIO_DEVICE_STATE_STOP)) {
> > -        /* TODO */
> > -        return ERR_PTR(-EOPNOTSUPP);
> > +        return NULL;
> >       }
> >         if ((cur_state == VFIO_DEVICE_STATE_STOP &&