On Thu, 16 May 2019 18:14:01 +0200 Eric Farman <farman@xxxxxxxxxxxxx> wrote: > The skip flag of a CCW offers the possibility of data not being > transferred, but is only meaningful for certain commands. > Specifically, it is only applicable for a read, read backward, sense, > or sense ID CCW and will be ignored for any other command code > (SA22-7832-11 page 15-64, and figure 15-30 on page 15-75). > > (A sense ID is xE4, while a sense is x04 with possible modifiers in the > upper four bits. So we will cover the whole "family" of sense CCWs.) > > For those scenarios, since there is no requirement for the target > address to be valid, we should skip the call to vfio_pin_pages() and > rely on the IDAL address we have allocated/built for the channel > program. The fact that the individual IDAWs within the IDAL are > invalid is fine, since they aren't actually checked in these cases. > > Set pa_nr to zero when skipping the pfn_array_pin() call, since it is > defined as the number of pages pinned and is used to determine > whether to call vfio_unpin_pages() upon cleanup. > > As we do this, since the pfn_array_pin() routine returns the number of > pages pinned, and we might not be doing that, the logic for converting > a CCW from direct-addressed to IDAL needs to ensure there is room for > one IDAW in the IDAL being built since a zero-length IDAL isn't great. I have now read this sentence several times and that this and that confuses me :) What are we doing, and what is the thing that we might not be doing? > > Signed-off-by: Eric Farman <farman@xxxxxxxxxxxxx> > --- > drivers/s390/cio/vfio_ccw_cp.c | 55 ++++++++++++++++++++++++++++++---- > 1 file changed, 50 insertions(+), 5 deletions(-)
