Re: [PATCH v3 0/6] vfio-ccw: support hsch/csch (kernel part)

[Eric Farman <farman@linux.ibm.com>]

On 02/06/2019 09:00 AM, Cornelia Huck wrote:
> On Wed, 30 Jan 2019 14:22:06 +0100
> Cornelia Huck <cohuck@redhat.com> wrote:
> 
>> [This is the Linux kernel part, git tree is available at
>> https://git.kernel.org/pub/scm/linux/kernel/git/kvms390/vfio-ccw.git vfio-ccw-eagain-caps-v3
> 
> I've pushed out the changes I've made so far (patch 1) to
> vfio-ccw-eagain-caps-v3.5. I'll wait a bit for more comments before
> sending a new version.
> 

Thanks for that branch...  For patch 1 in v3.5:

Reviewed-by: Eric Farman <farman@linux.ibm.com>

>>
>> The companion QEMU patches are available at
>> https://github.com/cohuck/qemu vfio-ccw-caps
>> This is the previously posted v2 version, which should continue to work.]
> 
> I would not mind if somebody looked at those as well :)

Not precluding anyone else from doing so :) ... I'd planned on looking 
at them as I get into the meat of patches 4-6 on the kernel side, where 
the overlap occurs.  I'm getting close.  :)

FWIW, I've been running with both series for the last week or two, along 
with some host kernel traces to prove things got executed the way I 
thought, and it's seemed to be working well.  So that makes me 
optimistic for the later patches.

  - Eric

> 
>>
>> Currently, vfio-ccw only relays START SUBCHANNEL requests to the real
>> device. This tends to work well for the most common 'good path' scenarios;
>> however, as we emulate {HALT,CLEAR} SUBCHANNEL in QEMU, things like
>> clearing pending requests at the device is currently not supported.
>> This may be a problem for e.g. error recovery.
>>
>> This patch series introduces capabilities (similar to what vfio-pci uses)
>> and exposes a new async region for handling hsch/csch.
>>
>> Lightly tested (I can interact with a dasd as before, and reserve/release
>> seems to work well.) Not sure if there is a better way to test this, ideas
>> welcome.
>>
>> Changes v2->v3:
>> - Unb0rked patch 1, improved scope
>> - Split out the new mutex from patch 2 into new patch 3; added missing
>>    locking and hopefully improved description
>> - Patch 2 now reworks the state handling by splitting the BUSY state
>>    into CP_PROCESSING and CP_PENDING
>> - Patches 3 and 5 adapted on top of the reworked patches; hsch/csch
>>    are allowed in CP_PENDING, but not in CP_PROCESSING (did not add
>>    any R-b due to that)
>> - Added missing free in patch 5
>> - Probably some small changes I forgot to note down
>>
>> Changes v1->v2:
>> - New patch 1: make it safe to use the cp accessors at any time; this
>>    should avoid problems with unsolicited interrupt handling
>> - New patch 2: handle concurrent accesses to the io region; the idea is
>>    to return -EAGAIN to userspace more often (so it can simply retry)
>> - also handle concurrent accesses to the async io region
>> - change VFIO_REGION_TYPE_CCW
>> - merge events for halt and clear to a single async event; this turned out
>>    to make the code quite a bit simpler
>> - probably some small changes I forgot to note down
>>
>> Cornelia Huck (6):
>>    vfio-ccw: make it safe to access channel programs
>>    vfio-ccw: rework ssch state handling
>>    vfio-ccw: protect the I/O region
>>    vfio-ccw: add capabilities chain
>>    s390/cio: export hsch to modules
>>    vfio-ccw: add handling for async channel instructions
>>
>>   drivers/s390/cio/Makefile           |   3 +-
>>   drivers/s390/cio/ioasm.c            |   1 +
>>   drivers/s390/cio/vfio_ccw_async.c   |  88 ++++++++++++
>>   drivers/s390/cio/vfio_ccw_cp.c      |  20 ++-
>>   drivers/s390/cio/vfio_ccw_cp.h      |   2 +
>>   drivers/s390/cio/vfio_ccw_drv.c     |  57 ++++++--
>>   drivers/s390/cio/vfio_ccw_fsm.c     | 143 ++++++++++++++++++-
>>   drivers/s390/cio/vfio_ccw_ops.c     | 210 +++++++++++++++++++++++-----
>>   drivers/s390/cio/vfio_ccw_private.h |  48 ++++++-
>>   include/uapi/linux/vfio.h           |   4 +
>>   include/uapi/linux/vfio_ccw.h       |  12 ++
>>   11 files changed, 531 insertions(+), 57 deletions(-)
>>   create mode 100644 drivers/s390/cio/vfio_ccw_async.c
>>
>