On 11/21/22 4:40 PM, Eric Farman wrote: > The rules of an IDAW are fairly simple: Each one can move no > more than a defined amount of data, must not cross the > boundary defined by that length, and must be aligned to that > length as well. The first IDAW in a list is special, in that > it does not need to adhere to that alignment, but the other > rules still apply. Thus, by reading the first IDAW in a list, > the number of IDAWs that will comprise a data transfer of a > particular size can be calculated. > > Let's factor out the reading of that first IDAW with the > logic that calculates the length of the list, to simplify > the rest of the routine that handles the individual IDAWs. > > Signed-off-by: Eric Farman <farman@xxxxxxxxxxxxx> > --- > drivers/s390/cio/vfio_ccw_cp.c | 39 ++++++++++++++++++++++++++-------- > 1 file changed, 30 insertions(+), 9 deletions(-) > > diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c > index a30f26962750..34a133d962d1 100644 > --- a/drivers/s390/cio/vfio_ccw_cp.c > +++ b/drivers/s390/cio/vfio_ccw_cp.c > @@ -496,23 +496,25 @@ static int ccwchain_fetch_tic(struct ccw1 *ccw, > return -EFAULT; > } > > -static int ccwchain_fetch_ccw(struct ccw1 *ccw, > - struct page_array *pa, > - struct channel_program *cp) > +/* > + * ccw_count_idaws() - Calculate the number of IDAWs needed to transfer > + * a specified amount of data > + * > + * @ccw: The Channel Command Word being translated > + * @cp: Channel Program being processed > + */ > +static int ccw_count_idaws(struct ccw1 *ccw, > + struct channel_program *cp) > { > struct vfio_device *vdev = > &container_of(cp, struct vfio_ccw_private, cp)->vdev; > u64 iova; > - unsigned long *idaws; > int ret; > int bytes = 1; > - int idaw_nr, idal_len; > - int i; > > if (ccw->count) > bytes = ccw->count; > > - /* Calculate size of IDAL */ > if (ccw_is_idal(ccw)) { > /* Read first IDAW to see if it's 4K-aligned or not. */ > /* All subsequent IDAws will be 4K-aligned. */ > @@ -522,7 +524,26 @@ static int ccwchain_fetch_ccw(struct ccw1 *ccw, > } else { > iova = ccw->cda; > } > - idaw_nr = idal_nr_words((void *)iova, bytes); > + > + return idal_nr_words((void *)iova, bytes); > +} > + > +static int ccwchain_fetch_ccw(struct ccw1 *ccw, > + struct page_array *pa, > + struct channel_program *cp) > +{ > + struct vfio_device *vdev = > + &container_of(cp, struct vfio_ccw_private, cp)->vdev; > + unsigned long *idaws; > + int ret; > + int idaw_nr, idal_len; > + int i; > + > + /* Calculate size of IDAL */ > + idaw_nr = ccw_count_idaws(ccw, cp); > + if (idaw_nr < 0) > + return idaw_nr; > + What about if we get a 0 back from ccw_count_idaws? The next thing we're going to do (not shown here) is kcalloc(0, sizeof(*idaws)), which I think means you'll get back ZERO_SIZE_PTR, not a null pointer. > idal_len = idaw_nr * sizeof(*idaws); > > /* Allocate an IDAL from host storage */ > @@ -555,7 +576,7 @@ static int ccwchain_fetch_ccw(struct ccw1 *ccw, > for (i = 0; i < idaw_nr; i++) > pa->pa_iova[i] = idaws[i]; > } else { > - pa->pa_iova[0] = iova; > + pa->pa_iova[0] = ccw->cda; > for (i = 1; i < pa->pa_nr; i++) > pa->pa_iova[i] = pa->pa_iova[i - 1] + PAGE_SIZE; > }