On 5/6/19 11:20 AM, Cornelia Huck wrote:
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 :/
Yup... :(
(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.
In an earlier version I had, I was re-purposing other fields in
pfn_array, which was rather kludgy. I could easily add a check for
non-zero pa_nr here, just to be clear of what we're doing (or in case we
decide TO check the return code from vfio_unpin_pages() some day).
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.
