On Fri, 3 May 2019 15:49:11 +0200 Eric Farman <farman@xxxxxxxxxxxxx> wrote: > If a CCW has a count of zero, then no data will be transferred and > pinning/unpinning memory is unnecessary. > > In addition to that, 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). This made me look at QEMU, and it seems that we cheerfully ignore that flag so far in our ccw interpretation code :/ > > (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 all 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. This will cause the vfio unpin > logic to return -EINVAL, but since the return code is not checked it > will not harm our cleanup path. We could also try to skip the unpinning, but this works as well. > > 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. > > Signed-off-by: Eric Farman <farman@xxxxxxxxxxxxx> > --- > drivers/s390/cio/vfio_ccw_cp.c | 61 +++++++++++++++++++++++++++++++++++++----- > 1 file changed, 55 insertions(+), 6 deletions(-) Looks good to me.
