On Thu, 6 Jun 2019 22:28:27 +0200 Eric Farman <farman@xxxxxxxxxxxxx> wrote: > While processing a channel program, we currently have two nested > arrays that carry a slightly different structure. The direct CCW > path creates this: > > ccwchain->pfn_array_table[1]->pfn_array[#pages] > > while an IDA CCW creates: > > ccwchain->pfn_array_table[#idaws]->pfn_array[1] > > The distinction appears to state that each pfn_array_table entry > points to an array of contiguous pages, represented by a pfn_array, > um, array. Since the direct-addressed scenario can ONLY represent > contiguous pages, it makes the intermediate array necessary but > difficult to recognize. Meanwhile, since an IDAL can contain > non-contiguous pages and there is no logic in vfio-ccw to detect > adjacent IDAWs, it is the second array that is necessary but appearing > to be superfluous. > > I am not aware of any documentation that states the pfn_array[] needs > to be of contiguous pages; it is just what the code does today. > I don't see any reason for this either, let's just flip the IDA > codepath around so that it generates: > > ch_pat->pfn_array_table[1]->pfn_array[#idaws] > > This will bring it in line with the direct-addressed codepath, > so that we can understand the behavior of this memory regardless > of what type of CCW is being processed. And it means the casual > observer does not need to know/care whether the pfn_array[] > represents contiguous pages or not. > > NB: The existing vfio-ccw code only supports 4K-block Format-2 IDAs, > so that "#pages" == "#idaws" in this area. This means that we will > have difficulty with this overlap in terminology if support for > Format-1 or 2K-block Format-2 IDAs is ever added. I don't think that > this patch changes our ability to make that distinction. I agree; and knowing that later patches will simplify things further, I think it will even be easier to do than on the current code base. > > Signed-off-by: Eric Farman <farman@xxxxxxxxxxxxx> > --- > drivers/s390/cio/vfio_ccw_cp.c | 26 +++++++++++--------------- > 1 file changed, 11 insertions(+), 15 deletions(-) Reviewed-by: Cornelia Huck <cohuck@xxxxxxxxxx>
